clang/lib/Sema/SemaTemplateInstantiate.cpp

   1 //===------- SemaTemplateInstantiate.cpp - C++ Template Instantiation ------===/
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //===----------------------------------------------------------------------===/
   7 //
   8 //  This file implements C++ template instantiation.
   9 //
  10 //===----------------------------------------------------------------------===/
  11
  12 #include "TreeTransform.h"
  13 #include "clang/AST/ASTConcept.h"
  14 #include "clang/AST/ASTConsumer.h"
  15 #include "clang/AST/ASTContext.h"
  16 #include "clang/AST/ASTLambda.h"
  17 #include "clang/AST/ASTMutationListener.h"
  18 #include "clang/AST/DeclBase.h"
  19 #include "clang/AST/DeclTemplate.h"
  20 #include "clang/AST/Expr.h"
  21 #include "clang/AST/ExprConcepts.h"
  22 #include "clang/AST/PrettyDeclStackTrace.h"
  23 #include "clang/AST/Type.h"
  24 #include "clang/AST/TypeVisitor.h"
  25 #include "clang/Basic/LangOptions.h"
  26 #include "clang/Basic/Stack.h"
  27 #include "clang/Basic/TargetInfo.h"
  28 #include "clang/Sema/DeclSpec.h"
  29 #include "clang/Sema/EnterExpressionEvaluationContext.h"
  30 #include "clang/Sema/Initialization.h"
  31 #include "clang/Sema/Lookup.h"
  32 #include "clang/Sema/Sema.h"
  33 #include "clang/Sema/SemaConcept.h"
  34 #include "clang/Sema/SemaInternal.h"
  35 #include "clang/Sema/Template.h"
  36 #include "clang/Sema/TemplateDeduction.h"
  37 #include "clang/Sema/TemplateInstCallback.h"
  38 #include "llvm/ADT/ScopeExit.h"
  39 #include "llvm/ADT/StringExtras.h"
  40 #include "llvm/Support/ErrorHandling.h"
  41 #include "llvm/Support/TimeProfiler.h"
  42 #include <optional>
  43
  44 using namespace clang;
  45 using namespace sema;
  46
  47 //===----------------------------------------------------------------------===/
  48 // Template Instantiation Support
  49 //===----------------------------------------------------------------------===/
  50
  51 namespace {
  52 namespace TemplateInstArgsHelpers {
  53 struct Response {
  54   const Decl *NextDecl = nullptr;
  55   bool IsDone = false;
  56   bool ClearRelativeToPrimary = true;
  57   static Response Done() {
  58     Response R;
  59     R.IsDone = true;
  60     return R;
  61   }
  62   static Response ChangeDecl(const Decl *ND) {
  63     Response R;
  64     R.NextDecl = ND;
  65     return R;
  66   }
  67   static Response ChangeDecl(const DeclContext *Ctx) {
  68     Response R;
  69     R.NextDecl = Decl::castFromDeclContext(Ctx);
  70     return R;
  71   }
  72
  73   static Response UseNextDecl(const Decl *CurDecl) {
  74     return ChangeDecl(CurDecl->getDeclContext());
  75   }
  76
  77   static Response DontClearRelativeToPrimaryNextDecl(const Decl *CurDecl) {
  78     Response R = Response::UseNextDecl(CurDecl);
  79     R.ClearRelativeToPrimary = false;
  80     return R;
  81   }
  82 };
  83 // Add template arguments from a variable template instantiation.
  84 Response
  85 HandleVarTemplateSpec(const VarTemplateSpecializationDecl *VarTemplSpec,
  86                       MultiLevelTemplateArgumentList &Result,
  87                       bool SkipForSpecialization) {
  88   // For a class-scope explicit specialization, there are no template arguments
  89   // at this level, but there may be enclosing template arguments.
  90   if (VarTemplSpec->isClassScopeExplicitSpecialization())
  91     return Response::DontClearRelativeToPrimaryNextDecl(VarTemplSpec);
  92
  93   // We're done when we hit an explicit specialization.
  94   if (VarTemplSpec->getSpecializationKind() == TSK_ExplicitSpecialization &&
  95       !isa<VarTemplatePartialSpecializationDecl>(VarTemplSpec))
  96     return Response::Done();
  97
  98   // If this variable template specialization was instantiated from a
  99   // specialized member that is a variable template, we're done.
 100   assert(VarTemplSpec->getSpecializedTemplate() && "No variable template?");
 101   llvm::PointerUnion<VarTemplateDecl *, VarTemplatePartialSpecializationDecl *>
 102       Specialized = VarTemplSpec->getSpecializedTemplateOrPartial();
 103   if (VarTemplatePartialSpecializationDecl *Partial =
 104           Specialized.dyn_cast<VarTemplatePartialSpecializationDecl *>()) {
 105     if (!SkipForSpecialization)
 106       Result.addOuterTemplateArguments(
 107           Partial, VarTemplSpec->getTemplateInstantiationArgs().asArray(),
 108           /*Final=*/false);
 109     if (Partial->isMemberSpecialization())
 110       return Response::Done();
 111   } else {
 112     VarTemplateDecl *Tmpl = Specialized.get<VarTemplateDecl *>();
 113     if (!SkipForSpecialization)
 114       Result.addOuterTemplateArguments(
 115           Tmpl, VarTemplSpec->getTemplateInstantiationArgs().asArray(),
 116           /*Final=*/false);
 117     if (Tmpl->isMemberSpecialization())
 118       return Response::Done();
 119   }
 120   return Response::DontClearRelativeToPrimaryNextDecl(VarTemplSpec);
 121 }
 122
 123 // If we have a template template parameter with translation unit context,
 124 // then we're performing substitution into a default template argument of
 125 // this template template parameter before we've constructed the template
 126 // that will own this template template parameter. In this case, we
 127 // use empty template parameter lists for all of the outer templates
 128 // to avoid performing any substitutions.
 129 Response
 130 HandleDefaultTempArgIntoTempTempParam(const TemplateTemplateParmDecl *TTP,
 131                                       MultiLevelTemplateArgumentList &Result) {
 132   for (unsigned I = 0, N = TTP->getDepth() + 1; I != N; ++I)
 133     Result.addOuterTemplateArguments(std::nullopt);
 134   return Response::Done();
 135 }
 136
 137 Response HandlePartialClassTemplateSpec(
 138     const ClassTemplatePartialSpecializationDecl *PartialClassTemplSpec,
 139     MultiLevelTemplateArgumentList &Result, bool SkipForSpecialization) {
 140   if (!SkipForSpecialization)
 141       Result.addOuterRetainedLevels(PartialClassTemplSpec->getTemplateDepth());
 142   return Response::Done();
 143 }
 144
 145 // Add template arguments from a class template instantiation.
 146 Response
 147 HandleClassTemplateSpec(const ClassTemplateSpecializationDecl *ClassTemplSpec,
 148                         MultiLevelTemplateArgumentList &Result,
 149                         bool SkipForSpecialization) {
 150   if (!ClassTemplSpec->isClassScopeExplicitSpecialization()) {
 151     // We're done when we hit an explicit specialization.
 152     if (ClassTemplSpec->getSpecializationKind() == TSK_ExplicitSpecialization &&
 153         !isa<ClassTemplatePartialSpecializationDecl>(ClassTemplSpec))
 154       return Response::Done();
 155
 156     if (!SkipForSpecialization)
 157       Result.addOuterTemplateArguments(
 158           const_cast<ClassTemplateSpecializationDecl *>(ClassTemplSpec),
 159           ClassTemplSpec->getTemplateInstantiationArgs().asArray(),
 160           /*Final=*/false);
 161
 162     // If this class template specialization was instantiated from a
 163     // specialized member that is a class template, we're done.
 164     assert(ClassTemplSpec->getSpecializedTemplate() && "No class template?");
 165     if (ClassTemplSpec->getSpecializedTemplate()->isMemberSpecialization())
 166       return Response::Done();
 167
 168     // If this was instantiated from a partial template specialization, we need
 169     // to get the next level of declaration context from the partial
 170     // specialization, as the ClassTemplateSpecializationDecl's
 171     // DeclContext/LexicalDeclContext will be for the primary template.
 172     if (auto *InstFromPartialTempl = ClassTemplSpec->getSpecializedTemplateOrPartial()
 173                       .dyn_cast<ClassTemplatePartialSpecializationDecl *>())
 174       return Response::ChangeDecl(InstFromPartialTempl->getLexicalDeclContext());
 175   }
 176   return Response::UseNextDecl(ClassTemplSpec);
 177 }
 178
 179 Response HandleFunction(const FunctionDecl *Function,
 180                         MultiLevelTemplateArgumentList &Result,
 181                         const FunctionDecl *Pattern, bool RelativeToPrimary,
 182                         bool ForConstraintInstantiation) {
 183   // Add template arguments from a function template specialization.
 184   if (!RelativeToPrimary &&
 185       Function->getTemplateSpecializationKindForInstantiation() ==
 186           TSK_ExplicitSpecialization)
 187     return Response::Done();
 188
 189   if (!RelativeToPrimary &&
 190       Function->getTemplateSpecializationKind() == TSK_ExplicitSpecialization) {
 191     // This is an implicit instantiation of an explicit specialization. We
 192     // don't get any template arguments from this function but might get
 193     // some from an enclosing template.
 194     return Response::UseNextDecl(Function);
 195   } else if (const TemplateArgumentList *TemplateArgs =
 196                  Function->getTemplateSpecializationArgs()) {
 197     // Add the template arguments for this specialization.
 198     Result.addOuterTemplateArguments(const_cast<FunctionDecl *>(Function),
 199                                      TemplateArgs->asArray(),
 200                                      /*Final=*/false);
 201
 202     // If this function was instantiated from a specialized member that is
 203     // a function template, we're done.
 204     assert(Function->getPrimaryTemplate() && "No function template?");
 205     if (Function->getPrimaryTemplate()->isMemberSpecialization())
 206       return Response::Done();
 207
 208     // If this function is a generic lambda specialization, we are done.
 209     if (!ForConstraintInstantiation &&
 210         isGenericLambdaCallOperatorOrStaticInvokerSpecialization(Function))
 211       return Response::Done();
 212
 213   } else if (Function->getDescribedFunctionTemplate()) {
 214     assert(
 215         (ForConstraintInstantiation || Result.getNumSubstitutedLevels() == 0) &&
 216         "Outer template not instantiated?");
 217   }
 218   // If this is a friend or local declaration and it declares an entity at
 219   // namespace scope, take arguments from its lexical parent
 220   // instead of its semantic parent, unless of course the pattern we're
 221   // instantiating actually comes from the file's context!
 222   if ((Function->getFriendObjectKind() || Function->isLocalExternDecl()) &&
 223       Function->getNonTransparentDeclContext()->isFileContext() &&
 224       (!Pattern || !Pattern->getLexicalDeclContext()->isFileContext())) {
 225     return Response::ChangeDecl(Function->getLexicalDeclContext());
 226   }
 227   return Response::UseNextDecl(Function);
 228 }
 229
 230 Response HandleFunctionTemplateDecl(const FunctionTemplateDecl *FTD,
 231                                     MultiLevelTemplateArgumentList &Result) {
 232   if (!isa<ClassTemplateSpecializationDecl>(FTD->getDeclContext())) {
 233     Result.addOuterTemplateArguments(
 234         const_cast<FunctionTemplateDecl *>(FTD),
 235         const_cast<FunctionTemplateDecl *>(FTD)->getInjectedTemplateArgs(),
 236         /*Final=*/false);
 237
 238     NestedNameSpecifier *NNS = FTD->getTemplatedDecl()->getQualifier();
 239
 240     while (const Type *Ty = NNS ? NNS->getAsType() : nullptr) {
 241       if (NNS->isInstantiationDependent()) {
 242         if (const auto *TSTy = Ty->getAs<TemplateSpecializationType>())
 243           Result.addOuterTemplateArguments(
 244               const_cast<FunctionTemplateDecl *>(FTD), TSTy->template_arguments(),
 245               /*Final=*/false);
 246       }
 247
 248       NNS = NNS->getPrefix();
 249     }
 250   }
 251
 252   return Response::ChangeDecl(FTD->getLexicalDeclContext());
 253 }
 254
 255 Response HandleRecordDecl(const CXXRecordDecl *Rec,
 256                           MultiLevelTemplateArgumentList &Result,
 257                           ASTContext &Context,
 258                           bool ForConstraintInstantiation) {
 259   if (ClassTemplateDecl *ClassTemplate = Rec->getDescribedClassTemplate()) {
 260     assert(
 261         (ForConstraintInstantiation || Result.getNumSubstitutedLevels() == 0) &&
 262         "Outer template not instantiated?");
 263     if (ClassTemplate->isMemberSpecialization())
 264       return Response::Done();
 265     if (ForConstraintInstantiation)
 266       Result.addOuterTemplateArguments(const_cast<CXXRecordDecl *>(Rec),
 267                                        ClassTemplate->getInjectedTemplateArgs(),
 268                                        /*Final=*/false);
 269   }
 270
 271   if (const MemberSpecializationInfo *MSInfo =
 272           Rec->getMemberSpecializationInfo())
 273     if (MSInfo->getTemplateSpecializationKind() == TSK_ExplicitSpecialization)
 274       return Response::Done();
 275
 276   bool IsFriend = Rec->getFriendObjectKind() ||
 277                   (Rec->getDescribedClassTemplate() &&
 278                    Rec->getDescribedClassTemplate()->getFriendObjectKind());
 279   if (ForConstraintInstantiation && IsFriend &&
 280       Rec->getNonTransparentDeclContext()->isFileContext()) {
 281     return Response::ChangeDecl(Rec->getLexicalDeclContext());
 282   }
 283
 284   // This is to make sure we pick up the VarTemplateSpecializationDecl that this
 285   // lambda is defined inside of.
 286   if (Rec->isLambda())
 287     if (const Decl *LCD = Rec->getLambdaContextDecl())
 288       return Response::ChangeDecl(LCD);
 289
 290   return Response::UseNextDecl(Rec);
 291 }
 292
 293 Response HandleImplicitConceptSpecializationDecl(
 294     const ImplicitConceptSpecializationDecl *CSD,
 295     MultiLevelTemplateArgumentList &Result) {
 296   Result.addOuterTemplateArguments(
 297       const_cast<ImplicitConceptSpecializationDecl *>(CSD),
 298       CSD->getTemplateArguments(),
 299       /*Final=*/false);
 300   return Response::UseNextDecl(CSD);
 301 }
 302
 303 Response HandleGenericDeclContext(const Decl *CurDecl) {
 304   return Response::UseNextDecl(CurDecl);
 305 }
 306 } // namespace TemplateInstArgsHelpers
 307 } // namespace
 308
 309 /// Retrieve the template argument list(s) that should be used to
 310 /// instantiate the definition of the given declaration.
 311 ///
 312 /// \param ND the declaration for which we are computing template instantiation
 313 /// arguments.
 314 ///
 315 /// \param DC In the event we don't HAVE a declaration yet, we instead provide
 316 ///  the decl context where it will be created.  In this case, the `Innermost`
 317 ///  should likely be provided.  If ND is non-null, this is ignored.
 318 ///
 319 /// \param Innermost if non-NULL, specifies a template argument list for the
 320 /// template declaration passed as ND.
 321 ///
 322 /// \param RelativeToPrimary true if we should get the template
 323 /// arguments relative to the primary template, even when we're
 324 /// dealing with a specialization. This is only relevant for function
 325 /// template specializations.
 326 ///
 327 /// \param Pattern If non-NULL, indicates the pattern from which we will be
 328 /// instantiating the definition of the given declaration, \p ND. This is
 329 /// used to determine the proper set of template instantiation arguments for
 330 /// friend function template specializations.
 331 ///
 332 /// \param ForConstraintInstantiation when collecting arguments,
 333 /// ForConstraintInstantiation indicates we should continue looking when
 334 /// encountering a lambda generic call operator, and continue looking for
 335 /// arguments on an enclosing class template.
 336
 337 MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
 338     const NamedDecl *ND, const DeclContext *DC, bool Final,
 339     const TemplateArgumentList *Innermost, bool RelativeToPrimary,
 340     const FunctionDecl *Pattern, bool ForConstraintInstantiation,
 341     bool SkipForSpecialization) {
 342   assert((ND || DC) && "Can't find arguments for a decl if one isn't provided");
 343   // Accumulate the set of template argument lists in this structure.
 344   MultiLevelTemplateArgumentList Result;
 345
 346   using namespace TemplateInstArgsHelpers;
 347   const Decl *CurDecl = ND;
 348   if (Innermost) {
 349     Result.addOuterTemplateArguments(const_cast<NamedDecl *>(ND),
 350                                      Innermost->asArray(), Final);
 351     CurDecl = Response::UseNextDecl(ND).NextDecl;
 352   }
 353
 354   if (!ND)
 355     CurDecl = Decl::castFromDeclContext(DC);
 356
 357   while (!CurDecl->isFileContextDecl()) {
 358     Response R;
 359     if (const auto *VarTemplSpec =
 360             dyn_cast<VarTemplateSpecializationDecl>(CurDecl)) {
 361       R = HandleVarTemplateSpec(VarTemplSpec, Result, SkipForSpecialization);
 362     } else if (const auto *PartialClassTemplSpec =
 363                    dyn_cast<ClassTemplatePartialSpecializationDecl>(CurDecl)) {
 364       R = HandlePartialClassTemplateSpec(PartialClassTemplSpec, Result,
 365                                          SkipForSpecialization);
 366     } else if (const auto *ClassTemplSpec =
 367                    dyn_cast<ClassTemplateSpecializationDecl>(CurDecl)) {
 368       R = HandleClassTemplateSpec(ClassTemplSpec, Result,
 369                                   SkipForSpecialization);
 370     } else if (const auto *Function = dyn_cast<FunctionDecl>(CurDecl)) {
 371       R = HandleFunction(Function, Result, Pattern, RelativeToPrimary,
 372                          ForConstraintInstantiation);
 373     } else if (const auto *Rec = dyn_cast<CXXRecordDecl>(CurDecl)) {
 374       R = HandleRecordDecl(Rec, Result, Context, ForConstraintInstantiation);
 375     } else if (const auto *CSD =
 376                    dyn_cast<ImplicitConceptSpecializationDecl>(CurDecl)) {
 377       R = HandleImplicitConceptSpecializationDecl(CSD, Result);
 378     } else if (const auto *FTD = dyn_cast<FunctionTemplateDecl>(CurDecl)) {
 379       R = HandleFunctionTemplateDecl(FTD, Result);
 380     } else if (const auto *CTD = dyn_cast<ClassTemplateDecl>(CurDecl)) {
 381       R = Response::ChangeDecl(CTD->getLexicalDeclContext());
 382     } else if (!isa<DeclContext>(CurDecl)) {
 383       R = Response::DontClearRelativeToPrimaryNextDecl(CurDecl);
 384       if (CurDecl->getDeclContext()->isTranslationUnit()) {
 385         if (const auto *TTP = dyn_cast<TemplateTemplateParmDecl>(CurDecl)) {
 386           R = HandleDefaultTempArgIntoTempTempParam(TTP, Result);
 387         }
 388       }
 389     } else {
 390       R = HandleGenericDeclContext(CurDecl);
 391     }
 392
 393     if (R.IsDone)
 394       return Result;
 395     if (R.ClearRelativeToPrimary)
 396       RelativeToPrimary = false;
 397     assert(R.NextDecl);
 398     CurDecl = R.NextDecl;
 399   }
 400
 401   return Result;
 402 }
 403
 404 bool Sema::CodeSynthesisContext::isInstantiationRecord() const {
 405   switch (Kind) {
 406   case TemplateInstantiation:
 407   case ExceptionSpecInstantiation:
 408   case DefaultTemplateArgumentInstantiation:
 409   case DefaultFunctionArgumentInstantiation:
 410   case ExplicitTemplateArgumentSubstitution:
 411   case DeducedTemplateArgumentSubstitution:
 412   case PriorTemplateArgumentSubstitution:
 413   case ConstraintsCheck:
 414   case NestedRequirementConstraintsCheck:
 415     return true;
 416
 417   case RequirementInstantiation:
 418   case RequirementParameterInstantiation:
 419   case DefaultTemplateArgumentChecking:
 420   case DeclaringSpecialMember:
 421   case DeclaringImplicitEqualityComparison:
 422   case DefiningSynthesizedFunction:
 423   case ExceptionSpecEvaluation:
 424   case ConstraintSubstitution:
 425   case ParameterMappingSubstitution:
 426   case ConstraintNormalization:
 427   case RewritingOperatorAsSpaceship:
 428   case InitializingStructuredBinding:
 429   case MarkingClassDllexported:
 430   case BuildingBuiltinDumpStructCall:
 431   case LambdaExpressionSubstitution:
 432   case BuildingDeductionGuides:
 433     return false;
 434
 435   // This function should never be called when Kind's value is Memoization.
 436   case Memoization:
 437     break;
 438   }
 439
 440   llvm_unreachable("Invalid SynthesisKind!");
 441 }
 442
 443 Sema::InstantiatingTemplate::InstantiatingTemplate(
 444     Sema &SemaRef, CodeSynthesisContext::SynthesisKind Kind,
 445     SourceLocation PointOfInstantiation, SourceRange InstantiationRange,
 446     Decl *Entity, NamedDecl *Template, ArrayRef<TemplateArgument> TemplateArgs,
 447     sema::TemplateDeductionInfo *DeductionInfo)
 448     : SemaRef(SemaRef) {
 449   // Don't allow further instantiation if a fatal error and an uncompilable
 450   // error have occurred. Any diagnostics we might have raised will not be
 451   // visible, and we do not need to construct a correct AST.
 452   if (SemaRef.Diags.hasFatalErrorOccurred() &&
 453       SemaRef.hasUncompilableErrorOccurred()) {
 454     Invalid = true;
 455     return;
 456   }
 457   Invalid = CheckInstantiationDepth(PointOfInstantiation, InstantiationRange);
 458   if (!Invalid) {
 459     CodeSynthesisContext Inst;
 460     Inst.Kind = Kind;
 461     Inst.PointOfInstantiation = PointOfInstantiation;
 462     Inst.Entity = Entity;
 463     Inst.Template = Template;
 464     Inst.TemplateArgs = TemplateArgs.data();
 465     Inst.NumTemplateArgs = TemplateArgs.size();
 466     Inst.DeductionInfo = DeductionInfo;
 467     Inst.InstantiationRange = InstantiationRange;
 468     SemaRef.pushCodeSynthesisContext(Inst);
 469
 470     AlreadyInstantiating = !Inst.Entity ? false :
 471         !SemaRef.InstantiatingSpecializations
 472              .insert({Inst.Entity->getCanonicalDecl(), Inst.Kind})
 473              .second;
 474     atTemplateBegin(SemaRef.TemplateInstCallbacks, SemaRef, Inst);
 475   }
 476 }
 477
 478 Sema::InstantiatingTemplate::InstantiatingTemplate(
 479     Sema &SemaRef, SourceLocation PointOfInstantiation, Decl *Entity,
 480     SourceRange InstantiationRange)
 481     : InstantiatingTemplate(SemaRef,
 482                             CodeSynthesisContext::TemplateInstantiation,
 483                             PointOfInstantiation, InstantiationRange, Entity) {}
 484
 485 Sema::InstantiatingTemplate::InstantiatingTemplate(
 486     Sema &SemaRef, SourceLocation PointOfInstantiation, FunctionDecl *Entity,
 487     ExceptionSpecification, SourceRange InstantiationRange)
 488     : InstantiatingTemplate(
 489           SemaRef, CodeSynthesisContext::ExceptionSpecInstantiation,
 490           PointOfInstantiation, InstantiationRange, Entity) {}
 491
 492 Sema::InstantiatingTemplate::InstantiatingTemplate(
 493     Sema &SemaRef, SourceLocation PointOfInstantiation, TemplateParameter Param,
 494     TemplateDecl *Template, ArrayRef<TemplateArgument> TemplateArgs,
 495     SourceRange InstantiationRange)
 496     : InstantiatingTemplate(
 497           SemaRef,
 498           CodeSynthesisContext::DefaultTemplateArgumentInstantiation,
 499           PointOfInstantiation, InstantiationRange, getAsNamedDecl(Param),
 500           Template, TemplateArgs) {}
 501
 502 Sema::InstantiatingTemplate::InstantiatingTemplate(
 503     Sema &SemaRef, SourceLocation PointOfInstantiation,
 504     FunctionTemplateDecl *FunctionTemplate,
 505     ArrayRef<TemplateArgument> TemplateArgs,
 506     CodeSynthesisContext::SynthesisKind Kind,
 507     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
 508     : InstantiatingTemplate(SemaRef, Kind, PointOfInstantiation,
 509                             InstantiationRange, FunctionTemplate, nullptr,
 510                             TemplateArgs, &DeductionInfo) {
 511   assert(
 512     Kind == CodeSynthesisContext::ExplicitTemplateArgumentSubstitution ||
 513     Kind == CodeSynthesisContext::DeducedTemplateArgumentSubstitution);
 514 }
 515
 516 Sema::InstantiatingTemplate::InstantiatingTemplate(
 517     Sema &SemaRef, SourceLocation PointOfInstantiation,
 518     TemplateDecl *Template,
 519     ArrayRef<TemplateArgument> TemplateArgs,
 520     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
 521     : InstantiatingTemplate(
 522           SemaRef,
 523           CodeSynthesisContext::DeducedTemplateArgumentSubstitution,
 524           PointOfInstantiation, InstantiationRange, Template, nullptr,
 525           TemplateArgs, &DeductionInfo) {}
 526
 527 Sema::InstantiatingTemplate::InstantiatingTemplate(
 528     Sema &SemaRef, SourceLocation PointOfInstantiation,
 529     ClassTemplatePartialSpecializationDecl *PartialSpec,
 530     ArrayRef<TemplateArgument> TemplateArgs,
 531     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
 532     : InstantiatingTemplate(
 533           SemaRef,
 534           CodeSynthesisContext::DeducedTemplateArgumentSubstitution,
 535           PointOfInstantiation, InstantiationRange, PartialSpec, nullptr,
 536           TemplateArgs, &DeductionInfo) {}
 537
 538 Sema::InstantiatingTemplate::InstantiatingTemplate(
 539     Sema &SemaRef, SourceLocation PointOfInstantiation,
 540     VarTemplatePartialSpecializationDecl *PartialSpec,
 541     ArrayRef<TemplateArgument> TemplateArgs,
 542     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
 543     : InstantiatingTemplate(
 544           SemaRef,
 545           CodeSynthesisContext::DeducedTemplateArgumentSubstitution,
 546           PointOfInstantiation, InstantiationRange, PartialSpec, nullptr,
 547           TemplateArgs, &DeductionInfo) {}
 548
 549 Sema::InstantiatingTemplate::InstantiatingTemplate(
 550     Sema &SemaRef, SourceLocation PointOfInstantiation, ParmVarDecl *Param,
 551     ArrayRef<TemplateArgument> TemplateArgs, SourceRange InstantiationRange)
 552     : InstantiatingTemplate(
 553           SemaRef,
 554           CodeSynthesisContext::DefaultFunctionArgumentInstantiation,
 555           PointOfInstantiation, InstantiationRange, Param, nullptr,
 556           TemplateArgs) {}
 557
 558 Sema::InstantiatingTemplate::InstantiatingTemplate(
 559     Sema &SemaRef, SourceLocation PointOfInstantiation, NamedDecl *Template,
 560     NonTypeTemplateParmDecl *Param, ArrayRef<TemplateArgument> TemplateArgs,
 561     SourceRange InstantiationRange)
 562     : InstantiatingTemplate(
 563           SemaRef,
 564           CodeSynthesisContext::PriorTemplateArgumentSubstitution,
 565           PointOfInstantiation, InstantiationRange, Param, Template,
 566           TemplateArgs) {}
 567
 568 Sema::InstantiatingTemplate::InstantiatingTemplate(
 569     Sema &SemaRef, SourceLocation PointOfInstantiation, NamedDecl *Template,
 570     TemplateTemplateParmDecl *Param, ArrayRef<TemplateArgument> TemplateArgs,
 571     SourceRange InstantiationRange)
 572     : InstantiatingTemplate(
 573           SemaRef,
 574           CodeSynthesisContext::PriorTemplateArgumentSubstitution,
 575           PointOfInstantiation, InstantiationRange, Param, Template,
 576           TemplateArgs) {}
 577
 578 Sema::InstantiatingTemplate::InstantiatingTemplate(
 579     Sema &SemaRef, SourceLocation PointOfInstantiation, TemplateDecl *Template,
 580     NamedDecl *Param, ArrayRef<TemplateArgument> TemplateArgs,
 581     SourceRange InstantiationRange)
 582     : InstantiatingTemplate(
 583           SemaRef, CodeSynthesisContext::DefaultTemplateArgumentChecking,
 584           PointOfInstantiation, InstantiationRange, Param, Template,
 585           TemplateArgs) {}
 586
 587 Sema::InstantiatingTemplate::InstantiatingTemplate(
 588     Sema &SemaRef, SourceLocation PointOfInstantiation,
 589     concepts::Requirement *Req, sema::TemplateDeductionInfo &DeductionInfo,
 590     SourceRange InstantiationRange)
 591     : InstantiatingTemplate(
 592           SemaRef, CodeSynthesisContext::RequirementInstantiation,
 593           PointOfInstantiation, InstantiationRange, /*Entity=*/nullptr,
 594           /*Template=*/nullptr, /*TemplateArgs=*/std::nullopt, &DeductionInfo) {
 595 }
 596
 597 Sema::InstantiatingTemplate::InstantiatingTemplate(
 598     Sema &SemaRef, SourceLocation PointOfInstantiation,
 599     concepts::NestedRequirement *Req, ConstraintsCheck,
 600     SourceRange InstantiationRange)
 601     : InstantiatingTemplate(
 602           SemaRef, CodeSynthesisContext::NestedRequirementConstraintsCheck,
 603           PointOfInstantiation, InstantiationRange, /*Entity=*/nullptr,
 604           /*Template=*/nullptr, /*TemplateArgs=*/std::nullopt) {}
 605
 606 Sema::InstantiatingTemplate::InstantiatingTemplate(
 607     Sema &SemaRef, SourceLocation PointOfInstantiation, const RequiresExpr *RE,
 608     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
 609     : InstantiatingTemplate(
 610           SemaRef, CodeSynthesisContext::RequirementParameterInstantiation,
 611           PointOfInstantiation, InstantiationRange, /*Entity=*/nullptr,
 612           /*Template=*/nullptr, /*TemplateArgs=*/std::nullopt, &DeductionInfo) {
 613 }
 614
 615 Sema::InstantiatingTemplate::InstantiatingTemplate(
 616     Sema &SemaRef, SourceLocation PointOfInstantiation,
 617     ConstraintsCheck, NamedDecl *Template,
 618     ArrayRef<TemplateArgument> TemplateArgs, SourceRange InstantiationRange)
 619     : InstantiatingTemplate(
 620           SemaRef, CodeSynthesisContext::ConstraintsCheck,
 621           PointOfInstantiation, InstantiationRange, Template, nullptr,
 622           TemplateArgs) {}
 623
 624 Sema::InstantiatingTemplate::InstantiatingTemplate(
 625     Sema &SemaRef, SourceLocation PointOfInstantiation,
 626     ConstraintSubstitution, NamedDecl *Template,
 627     sema::TemplateDeductionInfo &DeductionInfo, SourceRange InstantiationRange)
 628     : InstantiatingTemplate(
 629           SemaRef, CodeSynthesisContext::ConstraintSubstitution,
 630           PointOfInstantiation, InstantiationRange, Template, nullptr,
 631           {}, &DeductionInfo) {}
 632
 633 Sema::InstantiatingTemplate::InstantiatingTemplate(
 634     Sema &SemaRef, SourceLocation PointOfInstantiation,
 635     ConstraintNormalization, NamedDecl *Template,
 636     SourceRange InstantiationRange)
 637     : InstantiatingTemplate(
 638           SemaRef, CodeSynthesisContext::ConstraintNormalization,
 639           PointOfInstantiation, InstantiationRange, Template) {}
 640
 641 Sema::InstantiatingTemplate::InstantiatingTemplate(
 642     Sema &SemaRef, SourceLocation PointOfInstantiation,
 643     ParameterMappingSubstitution, NamedDecl *Template,
 644     SourceRange InstantiationRange)
 645     : InstantiatingTemplate(
 646           SemaRef, CodeSynthesisContext::ParameterMappingSubstitution,
 647           PointOfInstantiation, InstantiationRange, Template) {}
 648
 649 Sema::InstantiatingTemplate::InstantiatingTemplate(
 650     Sema &SemaRef, SourceLocation PointOfInstantiation, TemplateDecl *Entity,
 651     BuildingDeductionGuidesTag, SourceRange InstantiationRange)
 652     : InstantiatingTemplate(
 653           SemaRef, CodeSynthesisContext::BuildingDeductionGuides,
 654           PointOfInstantiation, InstantiationRange, Entity) {}
 655
 656
 657 void Sema::pushCodeSynthesisContext(CodeSynthesisContext Ctx) {
 658   Ctx.SavedInNonInstantiationSFINAEContext = InNonInstantiationSFINAEContext;
 659   InNonInstantiationSFINAEContext = false;
 660
 661   CodeSynthesisContexts.push_back(Ctx);
 662
 663   if (!Ctx.isInstantiationRecord())
 664     ++NonInstantiationEntries;
 665
 666   // Check to see if we're low on stack space. We can't do anything about this
 667   // from here, but we can at least warn the user.
 668   if (isStackNearlyExhausted())
 669     warnStackExhausted(Ctx.PointOfInstantiation);
 670 }
 671
 672 void Sema::popCodeSynthesisContext() {
 673   auto &Active = CodeSynthesisContexts.back();
 674   if (!Active.isInstantiationRecord()) {
 675     assert(NonInstantiationEntries > 0);
 676     --NonInstantiationEntries;
 677   }
 678
 679   InNonInstantiationSFINAEContext = Active.SavedInNonInstantiationSFINAEContext;
 680
 681   // Name lookup no longer looks in this template's defining module.
 682   assert(CodeSynthesisContexts.size() >=
 683              CodeSynthesisContextLookupModules.size() &&
 684          "forgot to remove a lookup module for a template instantiation");
 685   if (CodeSynthesisContexts.size() ==
 686       CodeSynthesisContextLookupModules.size()) {
 687     if (Module *M = CodeSynthesisContextLookupModules.back())
 688       LookupModulesCache.erase(M);
 689     CodeSynthesisContextLookupModules.pop_back();
 690   }
 691
 692   // If we've left the code synthesis context for the current context stack,
 693   // stop remembering that we've emitted that stack.
 694   if (CodeSynthesisContexts.size() ==
 695       LastEmittedCodeSynthesisContextDepth)
 696     LastEmittedCodeSynthesisContextDepth = 0;
 697
 698   CodeSynthesisContexts.pop_back();
 699 }
 700
 701 void Sema::InstantiatingTemplate::Clear() {
 702   if (!Invalid) {
 703     if (!AlreadyInstantiating) {
 704       auto &Active = SemaRef.CodeSynthesisContexts.back();
 705       if (Active.Entity)
 706         SemaRef.InstantiatingSpecializations.erase(
 707             {Active.Entity->getCanonicalDecl(), Active.Kind});
 708     }
 709
 710     atTemplateEnd(SemaRef.TemplateInstCallbacks, SemaRef,
 711                   SemaRef.CodeSynthesisContexts.back());
 712
 713     SemaRef.popCodeSynthesisContext();
 714     Invalid = true;
 715   }
 716 }
 717
 718 static std::string convertCallArgsToString(Sema &S,
 719                                            llvm::ArrayRef<const Expr *> Args) {
 720   std::string Result;
 721   llvm::raw_string_ostream OS(Result);
 722   llvm::ListSeparator Comma;
 723   for (const Expr *Arg : Args) {
 724     OS << Comma;
 725     Arg->IgnoreParens()->printPretty(OS, nullptr,
 726                                      S.Context.getPrintingPolicy());
 727   }
 728   return Result;
 729 }
 730
 731 bool Sema::InstantiatingTemplate::CheckInstantiationDepth(
 732                                         SourceLocation PointOfInstantiation,
 733                                            SourceRange InstantiationRange) {
 734   assert(SemaRef.NonInstantiationEntries <=
 735          SemaRef.CodeSynthesisContexts.size());
 736   if ((SemaRef.CodeSynthesisContexts.size() -
 737           SemaRef.NonInstantiationEntries)
 738         <= SemaRef.getLangOpts().InstantiationDepth)
 739     return false;
 740
 741   SemaRef.Diag(PointOfInstantiation,
 742                diag::err_template_recursion_depth_exceeded)
 743     << SemaRef.getLangOpts().InstantiationDepth
 744     << InstantiationRange;
 745   SemaRef.Diag(PointOfInstantiation, diag::note_template_recursion_depth)
 746     << SemaRef.getLangOpts().InstantiationDepth;
 747   return true;
 748 }
 749
 750 /// Prints the current instantiation stack through a series of
 751 /// notes.
 752 void Sema::PrintInstantiationStack() {
 753   // Determine which template instantiations to skip, if any.
 754   unsigned SkipStart = CodeSynthesisContexts.size(), SkipEnd = SkipStart;
 755   unsigned Limit = Diags.getTemplateBacktraceLimit();
 756   if (Limit && Limit < CodeSynthesisContexts.size()) {
 757     SkipStart = Limit / 2 + Limit % 2;
 758     SkipEnd = CodeSynthesisContexts.size() - Limit / 2;
 759   }
 760
 761   // FIXME: In all of these cases, we need to show the template arguments
 762   unsigned InstantiationIdx = 0;
 763   for (SmallVectorImpl<CodeSynthesisContext>::reverse_iterator
 764          Active = CodeSynthesisContexts.rbegin(),
 765          ActiveEnd = CodeSynthesisContexts.rend();
 766        Active != ActiveEnd;
 767        ++Active, ++InstantiationIdx) {
 768     // Skip this instantiation?
 769     if (InstantiationIdx >= SkipStart && InstantiationIdx < SkipEnd) {
 770       if (InstantiationIdx == SkipStart) {
 771         // Note that we're skipping instantiations.
 772         Diags.Report(Active->PointOfInstantiation,
 773                      diag::note_instantiation_contexts_suppressed)
 774           << unsigned(CodeSynthesisContexts.size() - Limit);
 775       }
 776       continue;
 777     }
 778
 779     switch (Active->Kind) {
 780     case CodeSynthesisContext::TemplateInstantiation: {
 781       Decl *D = Active->Entity;
 782       if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(D)) {
 783         unsigned DiagID = diag::note_template_member_class_here;
 784         if (isa<ClassTemplateSpecializationDecl>(Record))
 785           DiagID = diag::note_template_class_instantiation_here;
 786         Diags.Report(Active->PointOfInstantiation, DiagID)
 787           << Record << Active->InstantiationRange;
 788       } else if (FunctionDecl *Function = dyn_cast<FunctionDecl>(D)) {
 789         unsigned DiagID;
 790         if (Function->getPrimaryTemplate())
 791           DiagID = diag::note_function_template_spec_here;
 792         else
 793           DiagID = diag::note_template_member_function_here;
 794         Diags.Report(Active->PointOfInstantiation, DiagID)
 795           << Function
 796           << Active->InstantiationRange;
 797       } else if (VarDecl *VD = dyn_cast<VarDecl>(D)) {
 798         Diags.Report(Active->PointOfInstantiation,
 799                      VD->isStaticDataMember()?
 800                        diag::note_template_static_data_member_def_here
 801                      : diag::note_template_variable_def_here)
 802           << VD
 803           << Active->InstantiationRange;
 804       } else if (EnumDecl *ED = dyn_cast<EnumDecl>(D)) {
 805         Diags.Report(Active->PointOfInstantiation,
 806                      diag::note_template_enum_def_here)
 807           << ED
 808           << Active->InstantiationRange;
 809       } else if (FieldDecl *FD = dyn_cast<FieldDecl>(D)) {
 810         Diags.Report(Active->PointOfInstantiation,
 811                      diag::note_template_nsdmi_here)
 812             << FD << Active->InstantiationRange;
 813       } else {
 814         Diags.Report(Active->PointOfInstantiation,
 815                      diag::note_template_type_alias_instantiation_here)
 816           << cast<TypeAliasTemplateDecl>(D)
 817           << Active->InstantiationRange;
 818       }
 819       break;
 820     }
 821
 822     case CodeSynthesisContext::DefaultTemplateArgumentInstantiation: {
 823       TemplateDecl *Template = cast<TemplateDecl>(Active->Template);
 824       SmallString<128> TemplateArgsStr;
 825       llvm::raw_svector_ostream OS(TemplateArgsStr);
 826       Template->printName(OS, getPrintingPolicy());
 827       printTemplateArgumentList(OS, Active->template_arguments(),
 828                                 getPrintingPolicy());
 829       Diags.Report(Active->PointOfInstantiation,
 830                    diag::note_default_arg_instantiation_here)
 831         << OS.str()
 832         << Active->InstantiationRange;
 833       break;
 834     }
 835
 836     case CodeSynthesisContext::ExplicitTemplateArgumentSubstitution: {
 837       FunctionTemplateDecl *FnTmpl = cast<FunctionTemplateDecl>(Active->Entity);
 838       Diags.Report(Active->PointOfInstantiation,
 839                    diag::note_explicit_template_arg_substitution_here)
 840         << FnTmpl
 841         << getTemplateArgumentBindingsText(FnTmpl->getTemplateParameters(),
 842                                            Active->TemplateArgs,
 843                                            Active->NumTemplateArgs)
 844         << Active->InstantiationRange;
 845       break;
 846     }
 847
 848     case CodeSynthesisContext::DeducedTemplateArgumentSubstitution: {
 849       if (FunctionTemplateDecl *FnTmpl =
 850               dyn_cast<FunctionTemplateDecl>(Active->Entity)) {
 851         Diags.Report(Active->PointOfInstantiation,
 852                      diag::note_function_template_deduction_instantiation_here)
 853           << FnTmpl
 854           << getTemplateArgumentBindingsText(FnTmpl->getTemplateParameters(),
 855                                              Active->TemplateArgs,
 856                                              Active->NumTemplateArgs)
 857           << Active->InstantiationRange;
 858       } else {
 859         bool IsVar = isa<VarTemplateDecl>(Active->Entity) ||
 860                      isa<VarTemplateSpecializationDecl>(Active->Entity);
 861         bool IsTemplate = false;
 862         TemplateParameterList *Params;
 863         if (auto *D = dyn_cast<TemplateDecl>(Active->Entity)) {
 864           IsTemplate = true;
 865           Params = D->getTemplateParameters();
 866         } else if (auto *D = dyn_cast<ClassTemplatePartialSpecializationDecl>(
 867                        Active->Entity)) {
 868           Params = D->getTemplateParameters();
 869         } else if (auto *D = dyn_cast<VarTemplatePartialSpecializationDecl>(
 870                        Active->Entity)) {
 871           Params = D->getTemplateParameters();
 872         } else {
 873           llvm_unreachable("unexpected template kind");
 874         }
 875
 876         Diags.Report(Active->PointOfInstantiation,
 877                      diag::note_deduced_template_arg_substitution_here)
 878           << IsVar << IsTemplate << cast<NamedDecl>(Active->Entity)
 879           << getTemplateArgumentBindingsText(Params, Active->TemplateArgs,
 880                                              Active->NumTemplateArgs)
 881           << Active->InstantiationRange;
 882       }
 883       break;
 884     }
 885
 886     case CodeSynthesisContext::DefaultFunctionArgumentInstantiation: {
 887       ParmVarDecl *Param = cast<ParmVarDecl>(Active->Entity);
 888       FunctionDecl *FD = cast<FunctionDecl>(Param->getDeclContext());
 889
 890       SmallString<128> TemplateArgsStr;
 891       llvm::raw_svector_ostream OS(TemplateArgsStr);
 892       FD->printName(OS, getPrintingPolicy());
 893       printTemplateArgumentList(OS, Active->template_arguments(),
 894                                 getPrintingPolicy());
 895       Diags.Report(Active->PointOfInstantiation,
 896                    diag::note_default_function_arg_instantiation_here)
 897         << OS.str()
 898         << Active->InstantiationRange;
 899       break;
 900     }
 901
 902     case CodeSynthesisContext::PriorTemplateArgumentSubstitution: {
 903       NamedDecl *Parm = cast<NamedDecl>(Active->Entity);
 904       std::string Name;
 905       if (!Parm->getName().empty())
 906         Name = std::string(" '") + Parm->getName().str() + "'";
 907
 908       TemplateParameterList *TemplateParams = nullptr;
 909       if (TemplateDecl *Template = dyn_cast<TemplateDecl>(Active->Template))
 910         TemplateParams = Template->getTemplateParameters();
 911       else
 912         TemplateParams =
 913           cast<ClassTemplatePartialSpecializationDecl>(Active->Template)
 914                                                       ->getTemplateParameters();
 915       Diags.Report(Active->PointOfInstantiation,
 916                    diag::note_prior_template_arg_substitution)
 917         << isa<TemplateTemplateParmDecl>(Parm)
 918         << Name
 919         << getTemplateArgumentBindingsText(TemplateParams,
 920                                            Active->TemplateArgs,
 921                                            Active->NumTemplateArgs)
 922         << Active->InstantiationRange;
 923       break;
 924     }
 925
 926     case CodeSynthesisContext::DefaultTemplateArgumentChecking: {
 927       TemplateParameterList *TemplateParams = nullptr;
 928       if (TemplateDecl *Template = dyn_cast<TemplateDecl>(Active->Template))
 929         TemplateParams = Template->getTemplateParameters();
 930       else
 931         TemplateParams =
 932           cast<ClassTemplatePartialSpecializationDecl>(Active->Template)
 933                                                       ->getTemplateParameters();
 934
 935       Diags.Report(Active->PointOfInstantiation,
 936                    diag::note_template_default_arg_checking)
 937         << getTemplateArgumentBindingsText(TemplateParams,
 938                                            Active->TemplateArgs,
 939                                            Active->NumTemplateArgs)
 940         << Active->InstantiationRange;
 941       break;
 942     }
 943
 944     case CodeSynthesisContext::ExceptionSpecEvaluation:
 945       Diags.Report(Active->PointOfInstantiation,
 946                    diag::note_evaluating_exception_spec_here)
 947           << cast<FunctionDecl>(Active->Entity);
 948       break;
 949
 950     case CodeSynthesisContext::ExceptionSpecInstantiation:
 951       Diags.Report(Active->PointOfInstantiation,
 952                    diag::note_template_exception_spec_instantiation_here)
 953         << cast<FunctionDecl>(Active->Entity)
 954         << Active->InstantiationRange;
 955       break;
 956
 957     case CodeSynthesisContext::RequirementInstantiation:
 958       Diags.Report(Active->PointOfInstantiation,
 959                    diag::note_template_requirement_instantiation_here)
 960         << Active->InstantiationRange;
 961       break;
 962     case CodeSynthesisContext::RequirementParameterInstantiation:
 963       Diags.Report(Active->PointOfInstantiation,
 964                    diag::note_template_requirement_params_instantiation_here)
 965           << Active->InstantiationRange;
 966       break;
 967
 968     case CodeSynthesisContext::NestedRequirementConstraintsCheck:
 969       Diags.Report(Active->PointOfInstantiation,
 970                    diag::note_nested_requirement_here)
 971         << Active->InstantiationRange;
 972       break;
 973
 974     case CodeSynthesisContext::DeclaringSpecialMember:
 975       Diags.Report(Active->PointOfInstantiation,
 976                    diag::note_in_declaration_of_implicit_special_member)
 977         << cast<CXXRecordDecl>(Active->Entity) << Active->SpecialMember;
 978       break;
 979
 980     case CodeSynthesisContext::DeclaringImplicitEqualityComparison:
 981       Diags.Report(Active->Entity->getLocation(),
 982                    diag::note_in_declaration_of_implicit_equality_comparison);
 983       break;
 984
 985     case CodeSynthesisContext::DefiningSynthesizedFunction: {
 986       // FIXME: For synthesized functions that are not defaulted,
 987       // produce a note.
 988       auto *FD = dyn_cast<FunctionDecl>(Active->Entity);
 989       DefaultedFunctionKind DFK =
 990           FD ? getDefaultedFunctionKind(FD) : DefaultedFunctionKind();
 991       if (DFK.isSpecialMember()) {
 992         auto *MD = cast<CXXMethodDecl>(FD);
 993         Diags.Report(Active->PointOfInstantiation,
 994                      diag::note_member_synthesized_at)
 995             << MD->isExplicitlyDefaulted() << DFK.asSpecialMember()
 996             << Context.getTagDeclType(MD->getParent());
 997       } else if (DFK.isComparison()) {
 998         QualType RecordType = FD->getParamDecl(0)
 999                                   ->getType()
1000                                   .getNonReferenceType()
1001                                   .getUnqualifiedType();
1002         Diags.Report(Active->PointOfInstantiation,
1003                      diag::note_comparison_synthesized_at)
1004             << (int)DFK.asComparison() << RecordType;
1005       }
1006       break;
1007     }
1008
1009     case CodeSynthesisContext::RewritingOperatorAsSpaceship:
1010       Diags.Report(Active->Entity->getLocation(),
1011                    diag::note_rewriting_operator_as_spaceship);
1012       break;
1013
1014     case CodeSynthesisContext::InitializingStructuredBinding:
1015       Diags.Report(Active->PointOfInstantiation,
1016                    diag::note_in_binding_decl_init)
1017           << cast<BindingDecl>(Active->Entity);
1018       break;
1019
1020     case CodeSynthesisContext::MarkingClassDllexported:
1021       Diags.Report(Active->PointOfInstantiation,
1022                    diag::note_due_to_dllexported_class)
1023           << cast<CXXRecordDecl>(Active->Entity) << !getLangOpts().CPlusPlus11;
1024       break;
1025
1026     case CodeSynthesisContext::BuildingBuiltinDumpStructCall:
1027       Diags.Report(Active->PointOfInstantiation,
1028                    diag::note_building_builtin_dump_struct_call)
1029           << convertCallArgsToString(
1030                  *this, llvm::ArrayRef(Active->CallArgs, Active->NumCallArgs));
1031       break;
1032
1033     case CodeSynthesisContext::Memoization:
1034       break;
1035
1036     case CodeSynthesisContext::LambdaExpressionSubstitution:
1037       Diags.Report(Active->PointOfInstantiation,
1038                    diag::note_lambda_substitution_here);
1039       break;
1040     case CodeSynthesisContext::ConstraintsCheck: {
1041       unsigned DiagID = 0;
1042       if (!Active->Entity) {
1043         Diags.Report(Active->PointOfInstantiation,
1044                      diag::note_nested_requirement_here)
1045           << Active->InstantiationRange;
1046         break;
1047       }
1048       if (isa<ConceptDecl>(Active->Entity))
1049         DiagID = diag::note_concept_specialization_here;
1050       else if (isa<TemplateDecl>(Active->Entity))
1051         DiagID = diag::note_checking_constraints_for_template_id_here;
1052       else if (isa<VarTemplatePartialSpecializationDecl>(Active->Entity))
1053         DiagID = diag::note_checking_constraints_for_var_spec_id_here;
1054       else if (isa<ClassTemplatePartialSpecializationDecl>(Active->Entity))
1055         DiagID = diag::note_checking_constraints_for_class_spec_id_here;
1056       else {
1057         assert(isa<FunctionDecl>(Active->Entity));
1058         DiagID = diag::note_checking_constraints_for_function_here;
1059       }
1060       SmallString<128> TemplateArgsStr;
1061       llvm::raw_svector_ostream OS(TemplateArgsStr);
1062       cast<NamedDecl>(Active->Entity)->printName(OS, getPrintingPolicy());
1063       if (!isa<FunctionDecl>(Active->Entity)) {
1064         printTemplateArgumentList(OS, Active->template_arguments(),
1065                                   getPrintingPolicy());
1066       }
1067       Diags.Report(Active->PointOfInstantiation, DiagID) << OS.str()
1068         << Active->InstantiationRange;
1069       break;
1070     }
1071     case CodeSynthesisContext::ConstraintSubstitution:
1072       Diags.Report(Active->PointOfInstantiation,
1073                    diag::note_constraint_substitution_here)
1074           << Active->InstantiationRange;
1075       break;
1076     case CodeSynthesisContext::ConstraintNormalization:
1077       Diags.Report(Active->PointOfInstantiation,
1078                    diag::note_constraint_normalization_here)
1079           << cast<NamedDecl>(Active->Entity)->getName()
1080           << Active->InstantiationRange;
1081       break;
1082     case CodeSynthesisContext::ParameterMappingSubstitution:
1083       Diags.Report(Active->PointOfInstantiation,
1084                    diag::note_parameter_mapping_substitution_here)
1085           << Active->InstantiationRange;
1086       break;
1087     case CodeSynthesisContext::BuildingDeductionGuides:
1088       Diags.Report(Active->PointOfInstantiation,
1089                    diag::note_building_deduction_guide_here);
1090       break;
1091     }
1092   }
1093 }
1094
1095 std::optional<TemplateDeductionInfo *> Sema::isSFINAEContext() const {
1096   if (InNonInstantiationSFINAEContext)
1097     return std::optional<TemplateDeductionInfo *>(nullptr);
1098
1099   for (SmallVectorImpl<CodeSynthesisContext>::const_reverse_iterator
1100          Active = CodeSynthesisContexts.rbegin(),
1101          ActiveEnd = CodeSynthesisContexts.rend();
1102        Active != ActiveEnd;
1103        ++Active)
1104   {
1105     switch (Active->Kind) {
1106     case CodeSynthesisContext::TemplateInstantiation:
1107       // An instantiation of an alias template may or may not be a SFINAE
1108       // context, depending on what else is on the stack.
1109       if (isa<TypeAliasTemplateDecl>(Active->Entity))
1110         break;
1111       [[fallthrough]];
1112     case CodeSynthesisContext::DefaultFunctionArgumentInstantiation:
1113     case CodeSynthesisContext::ExceptionSpecInstantiation:
1114     case CodeSynthesisContext::ConstraintsCheck:
1115     case CodeSynthesisContext::ParameterMappingSubstitution:
1116     case CodeSynthesisContext::ConstraintNormalization:
1117     case CodeSynthesisContext::NestedRequirementConstraintsCheck:
1118       // This is a template instantiation, so there is no SFINAE.
1119       return std::nullopt;
1120     case CodeSynthesisContext::LambdaExpressionSubstitution:
1121       // [temp.deduct]p9
1122       // A lambda-expression appearing in a function type or a template
1123       // parameter is not considered part of the immediate context for the
1124       // purposes of template argument deduction.
1125       // CWG2672: A lambda-expression body is never in the immediate context.
1126       return std::nullopt;
1127
1128     case CodeSynthesisContext::DefaultTemplateArgumentInstantiation:
1129     case CodeSynthesisContext::PriorTemplateArgumentSubstitution:
1130     case CodeSynthesisContext::DefaultTemplateArgumentChecking:
1131     case CodeSynthesisContext::RewritingOperatorAsSpaceship:
1132       // A default template argument instantiation and substitution into
1133       // template parameters with arguments for prior parameters may or may
1134       // not be a SFINAE context; look further up the stack.
1135       break;
1136
1137     case CodeSynthesisContext::ExplicitTemplateArgumentSubstitution:
1138     case CodeSynthesisContext::DeducedTemplateArgumentSubstitution:
1139       // We're either substituting explicitly-specified template arguments,
1140       // deduced template arguments. SFINAE applies unless we are in a lambda
1141       // expression, see [temp.deduct]p9.
1142       [[fallthrough]];
1143     case CodeSynthesisContext::ConstraintSubstitution:
1144     case CodeSynthesisContext::RequirementInstantiation:
1145     case CodeSynthesisContext::RequirementParameterInstantiation:
1146       // SFINAE always applies in a constraint expression or a requirement
1147       // in a requires expression.
1148       assert(Active->DeductionInfo && "Missing deduction info pointer");
1149       return Active->DeductionInfo;
1150
1151     case CodeSynthesisContext::DeclaringSpecialMember:
1152     case CodeSynthesisContext::DeclaringImplicitEqualityComparison:
1153     case CodeSynthesisContext::DefiningSynthesizedFunction:
1154     case CodeSynthesisContext::InitializingStructuredBinding:
1155     case CodeSynthesisContext::MarkingClassDllexported:
1156     case CodeSynthesisContext::BuildingBuiltinDumpStructCall:
1157     case CodeSynthesisContext::BuildingDeductionGuides:
1158       // This happens in a context unrelated to template instantiation, so
1159       // there is no SFINAE.
1160       return std::nullopt;
1161
1162     case CodeSynthesisContext::ExceptionSpecEvaluation:
1163       // FIXME: This should not be treated as a SFINAE context, because
1164       // we will cache an incorrect exception specification. However, clang
1165       // bootstrap relies this! See PR31692.
1166       break;
1167
1168     case CodeSynthesisContext::Memoization:
1169       break;
1170     }
1171
1172     // The inner context was transparent for SFINAE. If it occurred within a
1173     // non-instantiation SFINAE context, then SFINAE applies.
1174     if (Active->SavedInNonInstantiationSFINAEContext)
1175       return std::optional<TemplateDeductionInfo *>(nullptr);
1176   }
1177
1178   return std::nullopt;
1179 }
1180
1181 //===----------------------------------------------------------------------===/
1182 // Template Instantiation for Types
1183 //===----------------------------------------------------------------------===/
1184 namespace {
1185   class TemplateInstantiator : public TreeTransform<TemplateInstantiator> {
1186     const MultiLevelTemplateArgumentList &TemplateArgs;
1187     SourceLocation Loc;
1188     DeclarationName Entity;
1189     bool EvaluateConstraints = true;
1190
1191   public:
1192     typedef TreeTransform<TemplateInstantiator> inherited;
1193
1194     TemplateInstantiator(Sema &SemaRef,
1195                          const MultiLevelTemplateArgumentList &TemplateArgs,
1196                          SourceLocation Loc, DeclarationName Entity)
1197         : inherited(SemaRef), TemplateArgs(TemplateArgs), Loc(Loc),
1198           Entity(Entity) {}
1199
1200     void setEvaluateConstraints(bool B) {
1201       EvaluateConstraints = B;
1202     }
1203     bool getEvaluateConstraints() {
1204       return EvaluateConstraints;
1205     }
1206
1207     /// Determine whether the given type \p T has already been
1208     /// transformed.
1209     ///
1210     /// For the purposes of template instantiation, a type has already been
1211     /// transformed if it is NULL or if it is not dependent.
1212     bool AlreadyTransformed(QualType T);
1213
1214     /// Returns the location of the entity being instantiated, if known.
1215     SourceLocation getBaseLocation() { return Loc; }
1216
1217     /// Returns the name of the entity being instantiated, if any.
1218     DeclarationName getBaseEntity() { return Entity; }
1219
1220     /// Sets the "base" location and entity when that
1221     /// information is known based on another transformation.
1222     void setBase(SourceLocation Loc, DeclarationName Entity) {
1223       this->Loc = Loc;
1224       this->Entity = Entity;
1225     }
1226
1227     unsigned TransformTemplateDepth(unsigned Depth) {
1228       return TemplateArgs.getNewDepth(Depth);
1229     }
1230
1231     std::optional<unsigned> getPackIndex(TemplateArgument Pack) {
1232       int Index = getSema().ArgumentPackSubstitutionIndex;
1233       if (Index == -1)
1234         return std::nullopt;
1235       return Pack.pack_size() - 1 - Index;
1236     }
1237
1238     bool TryExpandParameterPacks(SourceLocation EllipsisLoc,
1239                                  SourceRange PatternRange,
1240                                  ArrayRef<UnexpandedParameterPack> Unexpanded,
1241                                  bool &ShouldExpand, bool &RetainExpansion,
1242                                  std::optional<unsigned> &NumExpansions) {
1243       return getSema().CheckParameterPacksForExpansion(EllipsisLoc,
1244                                                        PatternRange, Unexpanded,
1245                                                        TemplateArgs,
1246                                                        ShouldExpand,
1247                                                        RetainExpansion,
1248                                                        NumExpansions);
1249     }
1250
1251     void ExpandingFunctionParameterPack(ParmVarDecl *Pack) {
1252       SemaRef.CurrentInstantiationScope->MakeInstantiatedLocalArgPack(Pack);
1253     }
1254
1255     TemplateArgument ForgetPartiallySubstitutedPack() {
1256       TemplateArgument Result;
1257       if (NamedDecl *PartialPack
1258             = SemaRef.CurrentInstantiationScope->getPartiallySubstitutedPack()){
1259         MultiLevelTemplateArgumentList &TemplateArgs
1260           = const_cast<MultiLevelTemplateArgumentList &>(this->TemplateArgs);
1261         unsigned Depth, Index;
1262         std::tie(Depth, Index) = getDepthAndIndex(PartialPack);
1263         if (TemplateArgs.hasTemplateArgument(Depth, Index)) {
1264           Result = TemplateArgs(Depth, Index);
1265           TemplateArgs.setArgument(Depth, Index, TemplateArgument());
1266         }
1267       }
1268
1269       return Result;
1270     }
1271
1272     void RememberPartiallySubstitutedPack(TemplateArgument Arg) {
1273       if (Arg.isNull())
1274         return;
1275
1276       if (NamedDecl *PartialPack
1277             = SemaRef.CurrentInstantiationScope->getPartiallySubstitutedPack()){
1278         MultiLevelTemplateArgumentList &TemplateArgs
1279         = const_cast<MultiLevelTemplateArgumentList &>(this->TemplateArgs);
1280         unsigned Depth, Index;
1281         std::tie(Depth, Index) = getDepthAndIndex(PartialPack);
1282         TemplateArgs.setArgument(Depth, Index, Arg);
1283       }
1284     }
1285
1286     /// Transform the given declaration by instantiating a reference to
1287     /// this declaration.
1288     Decl *TransformDecl(SourceLocation Loc, Decl *D);
1289
1290     void transformAttrs(Decl *Old, Decl *New) {
1291       SemaRef.InstantiateAttrs(TemplateArgs, Old, New);
1292     }
1293
1294     void transformedLocalDecl(Decl *Old, ArrayRef<Decl *> NewDecls) {
1295       if (Old->isParameterPack()) {
1296         SemaRef.CurrentInstantiationScope->MakeInstantiatedLocalArgPack(Old);
1297         for (auto *New : NewDecls)
1298           SemaRef.CurrentInstantiationScope->InstantiatedLocalPackArg(
1299               Old, cast<VarDecl>(New));
1300         return;
1301       }
1302
1303       assert(NewDecls.size() == 1 &&
1304              "should only have multiple expansions for a pack");
1305       Decl *New = NewDecls.front();
1306
1307       // If we've instantiated the call operator of a lambda or the call
1308       // operator template of a generic lambda, update the "instantiation of"
1309       // information.
1310       auto *NewMD = dyn_cast<CXXMethodDecl>(New);
1311       if (NewMD && isLambdaCallOperator(NewMD)) {
1312         auto *OldMD = dyn_cast<CXXMethodDecl>(Old);
1313         if (auto *NewTD = NewMD->getDescribedFunctionTemplate())
1314           NewTD->setInstantiatedFromMemberTemplate(
1315               OldMD->getDescribedFunctionTemplate());
1316         else
1317           NewMD->setInstantiationOfMemberFunction(OldMD,
1318                                                   TSK_ImplicitInstantiation);
1319       }
1320
1321       SemaRef.CurrentInstantiationScope->InstantiatedLocal(Old, New);
1322
1323       // We recreated a local declaration, but not by instantiating it. There
1324       // may be pending dependent diagnostics to produce.
1325       if (auto *DC = dyn_cast<DeclContext>(Old);
1326           DC && DC->isDependentContext() && DC->isFunctionOrMethod())
1327         SemaRef.PerformDependentDiagnostics(DC, TemplateArgs);
1328     }
1329
1330     /// Transform the definition of the given declaration by
1331     /// instantiating it.
1332     Decl *TransformDefinition(SourceLocation Loc, Decl *D);
1333
1334     /// Transform the first qualifier within a scope by instantiating the
1335     /// declaration.
1336     NamedDecl *TransformFirstQualifierInScope(NamedDecl *D, SourceLocation Loc);
1337
1338     bool TransformExceptionSpec(SourceLocation Loc,
1339                                 FunctionProtoType::ExceptionSpecInfo &ESI,
1340                                 SmallVectorImpl<QualType> &Exceptions,
1341                                 bool &Changed);
1342
1343     /// Rebuild the exception declaration and register the declaration
1344     /// as an instantiated local.
1345     VarDecl *RebuildExceptionDecl(VarDecl *ExceptionDecl,
1346                                   TypeSourceInfo *Declarator,
1347                                   SourceLocation StartLoc,
1348                                   SourceLocation NameLoc,
1349                                   IdentifierInfo *Name);
1350
1351     /// Rebuild the Objective-C exception declaration and register the
1352     /// declaration as an instantiated local.
1353     VarDecl *RebuildObjCExceptionDecl(VarDecl *ExceptionDecl,
1354                                       TypeSourceInfo *TSInfo, QualType T);
1355
1356     /// Check for tag mismatches when instantiating an
1357     /// elaborated type.
1358     QualType RebuildElaboratedType(SourceLocation KeywordLoc,
1359                                    ElaboratedTypeKeyword Keyword,
1360                                    NestedNameSpecifierLoc QualifierLoc,
1361                                    QualType T);
1362
1363     TemplateName
1364     TransformTemplateName(CXXScopeSpec &SS, TemplateName Name,
1365                           SourceLocation NameLoc,
1366                           QualType ObjectType = QualType(),
1367                           NamedDecl *FirstQualifierInScope = nullptr,
1368                           bool AllowInjectedClassName = false);
1369
1370     const LoopHintAttr *TransformLoopHintAttr(const LoopHintAttr *LH);
1371     const NoInlineAttr *TransformStmtNoInlineAttr(const Stmt *OrigS,
1372                                                   const Stmt *InstS,
1373                                                   const NoInlineAttr *A);
1374     const AlwaysInlineAttr *
1375     TransformStmtAlwaysInlineAttr(const Stmt *OrigS, const Stmt *InstS,
1376                                   const AlwaysInlineAttr *A);
1377
1378     ExprResult TransformPredefinedExpr(PredefinedExpr *E);
1379     ExprResult TransformDeclRefExpr(DeclRefExpr *E);
1380     ExprResult TransformCXXDefaultArgExpr(CXXDefaultArgExpr *E);
1381
1382     ExprResult TransformTemplateParmRefExpr(DeclRefExpr *E,
1383                                             NonTypeTemplateParmDecl *D);
1384     ExprResult TransformSubstNonTypeTemplateParmPackExpr(
1385                                            SubstNonTypeTemplateParmPackExpr *E);
1386     ExprResult TransformSubstNonTypeTemplateParmExpr(
1387                                            SubstNonTypeTemplateParmExpr *E);
1388
1389     /// Rebuild a DeclRefExpr for a VarDecl reference.
1390     ExprResult RebuildVarDeclRefExpr(VarDecl *PD, SourceLocation Loc);
1391
1392     /// Transform a reference to a function or init-capture parameter pack.
1393     ExprResult TransformFunctionParmPackRefExpr(DeclRefExpr *E, VarDecl *PD);
1394
1395     /// Transform a FunctionParmPackExpr which was built when we couldn't
1396     /// expand a function parameter pack reference which refers to an expanded
1397     /// pack.
1398     ExprResult TransformFunctionParmPackExpr(FunctionParmPackExpr *E);
1399
1400     QualType TransformFunctionProtoType(TypeLocBuilder &TLB,
1401                                         FunctionProtoTypeLoc TL) {
1402       // Call the base version; it will forward to our overridden version below.
1403       return inherited::TransformFunctionProtoType(TLB, TL);
1404     }
1405
1406     template<typename Fn>
1407     QualType TransformFunctionProtoType(TypeLocBuilder &TLB,
1408                                         FunctionProtoTypeLoc TL,
1409                                         CXXRecordDecl *ThisContext,
1410                                         Qualifiers ThisTypeQuals,
1411                                         Fn TransformExceptionSpec);
1412
1413     ParmVarDecl *
1414     TransformFunctionTypeParam(ParmVarDecl *OldParm, int indexAdjustment,
1415                                std::optional<unsigned> NumExpansions,
1416                                bool ExpectParameterPack);
1417
1418     using inherited::TransformTemplateTypeParmType;
1419     /// Transforms a template type parameter type by performing
1420     /// substitution of the corresponding template type argument.
1421     QualType TransformTemplateTypeParmType(TypeLocBuilder &TLB,
1422                                            TemplateTypeParmTypeLoc TL,
1423                                            bool SuppressObjCLifetime);
1424
1425     QualType BuildSubstTemplateTypeParmType(
1426         TypeLocBuilder &TLB, bool SuppressObjCLifetime, bool Final,
1427         Decl *AssociatedDecl, unsigned Index, std::optional<unsigned> PackIndex,
1428         TemplateArgument Arg, SourceLocation NameLoc);
1429
1430     /// Transforms an already-substituted template type parameter pack
1431     /// into either itself (if we aren't substituting into its pack expansion)
1432     /// or the appropriate substituted argument.
1433     using inherited::TransformSubstTemplateTypeParmPackType;
1434     QualType
1435     TransformSubstTemplateTypeParmPackType(TypeLocBuilder &TLB,
1436                                            SubstTemplateTypeParmPackTypeLoc TL,
1437                                            bool SuppressObjCLifetime);
1438
1439     ExprResult TransformLambdaExpr(LambdaExpr *E) {
1440       LocalInstantiationScope Scope(SemaRef, /*CombineWithOuterScope=*/true);
1441       Sema::ConstraintEvalRAII<TemplateInstantiator> RAII(*this);
1442
1443       Sema::CodeSynthesisContext C;
1444       C.Kind = clang::Sema::CodeSynthesisContext::LambdaExpressionSubstitution;
1445       C.PointOfInstantiation = E->getBeginLoc();
1446       SemaRef.pushCodeSynthesisContext(C);
1447       auto PopCtx =
1448           llvm::make_scope_exit([this] { SemaRef.popCodeSynthesisContext(); });
1449
1450       ExprResult Result = inherited::TransformLambdaExpr(E);
1451       if (Result.isInvalid())
1452         return Result;
1453
1454       CXXMethodDecl *MD = Result.getAs<LambdaExpr>()->getCallOperator();
1455       for (ParmVarDecl *PVD : MD->parameters()) {
1456         assert(PVD && "null in a parameter list");
1457         if (!PVD->hasDefaultArg())
1458           continue;
1459         Expr *UninstExpr = PVD->getUninstantiatedDefaultArg();
1460         // FIXME: Obtain the source location for the '=' token.
1461         SourceLocation EqualLoc = UninstExpr->getBeginLoc();
1462         if (SemaRef.SubstDefaultArgument(EqualLoc, PVD, TemplateArgs)) {
1463           // If substitution fails, the default argument is set to a
1464           // RecoveryExpr that wraps the uninstantiated default argument so
1465           // that downstream diagnostics are omitted.
1466           ExprResult ErrorResult = SemaRef.CreateRecoveryExpr(
1467               UninstExpr->getBeginLoc(), UninstExpr->getEndLoc(),
1468               { UninstExpr }, UninstExpr->getType());
1469           if (ErrorResult.isUsable())
1470             PVD->setDefaultArg(ErrorResult.get());
1471         }
1472       }
1473
1474       return Result;
1475     }
1476
1477     ExprResult TransformRequiresExpr(RequiresExpr *E) {
1478       LocalInstantiationScope Scope(SemaRef, /*CombineWithOuterScope=*/true);
1479       ExprResult TransReq = inherited::TransformRequiresExpr(E);
1480       if (TransReq.isInvalid())
1481         return TransReq;
1482       assert(TransReq.get() != E &&
1483              "Do not change value of isSatisfied for the existing expression. "
1484              "Create a new expression instead.");
1485       if (E->getBody()->isDependentContext()) {
1486         Sema::SFINAETrap Trap(SemaRef);
1487         // We recreate the RequiresExpr body, but not by instantiating it.
1488         // Produce pending diagnostics for dependent access check.
1489         SemaRef.PerformDependentDiagnostics(E->getBody(), TemplateArgs);
1490         // FIXME: Store SFINAE diagnostics in RequiresExpr for diagnosis.
1491         if (Trap.hasErrorOccurred())
1492           TransReq.getAs<RequiresExpr>()->setSatisfied(false);
1493       }
1494       return TransReq;
1495     }
1496
1497     bool TransformRequiresExprRequirements(
1498         ArrayRef<concepts::Requirement *> Reqs,
1499         SmallVectorImpl<concepts::Requirement *> &Transformed) {
1500       bool SatisfactionDetermined = false;
1501       for (concepts::Requirement *Req : Reqs) {
1502         concepts::Requirement *TransReq = nullptr;
1503         if (!SatisfactionDetermined) {
1504           if (auto *TypeReq = dyn_cast<concepts::TypeRequirement>(Req))
1505             TransReq = TransformTypeRequirement(TypeReq);
1506           else if (auto *ExprReq = dyn_cast<concepts::ExprRequirement>(Req))
1507             TransReq = TransformExprRequirement(ExprReq);
1508           else
1509             TransReq = TransformNestedRequirement(
1510                 cast<concepts::NestedRequirement>(Req));
1511           if (!TransReq)
1512             return true;
1513           if (!TransReq->isDependent() && !TransReq->isSatisfied())
1514             // [expr.prim.req]p6
1515             //   [...]  The substitution and semantic constraint checking
1516             //   proceeds in lexical order and stops when a condition that
1517             //   determines the result of the requires-expression is
1518             //   encountered. [..]
1519             SatisfactionDetermined = true;
1520         } else
1521           TransReq = Req;
1522         Transformed.push_back(TransReq);
1523       }
1524       return false;
1525     }
1526
1527     TemplateParameterList *TransformTemplateParameterList(
1528                               TemplateParameterList *OrigTPL)  {
1529       if (!OrigTPL || !OrigTPL->size()) return OrigTPL;
1530
1531       DeclContext *Owner = OrigTPL->getParam(0)->getDeclContext();
1532       TemplateDeclInstantiator  DeclInstantiator(getSema(),
1533                         /* DeclContext *Owner */ Owner, TemplateArgs);
1534       DeclInstantiator.setEvaluateConstraints(EvaluateConstraints);
1535       return DeclInstantiator.SubstTemplateParams(OrigTPL);
1536     }
1537
1538     concepts::TypeRequirement *
1539     TransformTypeRequirement(concepts::TypeRequirement *Req);
1540     concepts::ExprRequirement *
1541     TransformExprRequirement(concepts::ExprRequirement *Req);
1542     concepts::NestedRequirement *
1543     TransformNestedRequirement(concepts::NestedRequirement *Req);
1544     ExprResult TransformRequiresTypeParams(
1545         SourceLocation KWLoc, SourceLocation RBraceLoc, const RequiresExpr *RE,
1546         RequiresExprBodyDecl *Body, ArrayRef<ParmVarDecl *> Params,
1547         SmallVectorImpl<QualType> &PTypes,
1548         SmallVectorImpl<ParmVarDecl *> &TransParams,
1549         Sema::ExtParameterInfoBuilder &PInfos);
1550
1551   private:
1552     ExprResult
1553     transformNonTypeTemplateParmRef(Decl *AssociatedDecl,
1554                                     const NonTypeTemplateParmDecl *parm,
1555                                     SourceLocation loc, TemplateArgument arg,
1556                                     std::optional<unsigned> PackIndex);
1557   };
1558 }
1559
1560 bool TemplateInstantiator::AlreadyTransformed(QualType T) {
1561   if (T.isNull())
1562     return true;
1563
1564   if (T->isInstantiationDependentType() || T->isVariablyModifiedType())
1565     return false;
1566
1567   getSema().MarkDeclarationsReferencedInType(Loc, T);
1568   return true;
1569 }
1570
1571 static TemplateArgument
1572 getPackSubstitutedTemplateArgument(Sema &S, TemplateArgument Arg) {
1573   assert(S.ArgumentPackSubstitutionIndex >= 0);
1574   assert(S.ArgumentPackSubstitutionIndex < (int)Arg.pack_size());
1575   Arg = Arg.pack_begin()[S.ArgumentPackSubstitutionIndex];
1576   if (Arg.isPackExpansion())
1577     Arg = Arg.getPackExpansionPattern();
1578   return Arg;
1579 }
1580
1581 Decl *TemplateInstantiator::TransformDecl(SourceLocation Loc, Decl *D) {
1582   if (!D)
1583     return nullptr;
1584
1585   if (TemplateTemplateParmDecl *TTP = dyn_cast<TemplateTemplateParmDecl>(D)) {
1586     if (TTP->getDepth() < TemplateArgs.getNumLevels()) {
1587       // If the corresponding template argument is NULL or non-existent, it's
1588       // because we are performing instantiation from explicitly-specified
1589       // template arguments in a function template, but there were some
1590       // arguments left unspecified.
1591       if (!TemplateArgs.hasTemplateArgument(TTP->getDepth(),
1592                                             TTP->getPosition()))
1593         return D;
1594
1595       TemplateArgument Arg = TemplateArgs(TTP->getDepth(), TTP->getPosition());
1596
1597       if (TTP->isParameterPack()) {
1598         assert(Arg.getKind() == TemplateArgument::Pack &&
1599                "Missing argument pack");
1600         Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
1601       }
1602
1603       TemplateName Template = Arg.getAsTemplate().getNameToSubstitute();
1604       assert(!Template.isNull() && Template.getAsTemplateDecl() &&
1605              "Wrong kind of template template argument");
1606       return Template.getAsTemplateDecl();
1607     }
1608
1609     // Fall through to find the instantiated declaration for this template
1610     // template parameter.
1611   }
1612
1613   return SemaRef.FindInstantiatedDecl(Loc, cast<NamedDecl>(D), TemplateArgs);
1614 }
1615
1616 Decl *TemplateInstantiator::TransformDefinition(SourceLocation Loc, Decl *D) {
1617   Decl *Inst = getSema().SubstDecl(D, getSema().CurContext, TemplateArgs);
1618   if (!Inst)
1619     return nullptr;
1620
1621   getSema().CurrentInstantiationScope->InstantiatedLocal(D, Inst);
1622   return Inst;
1623 }
1624
1625 bool TemplateInstantiator::TransformExceptionSpec(
1626     SourceLocation Loc, FunctionProtoType::ExceptionSpecInfo &ESI,
1627     SmallVectorImpl<QualType> &Exceptions, bool &Changed) {
1628   if (ESI.Type == EST_Uninstantiated) {
1629     ESI.NoexceptExpr = cast<FunctionProtoType>(ESI.SourceTemplate->getType())
1630                            ->getNoexceptExpr();
1631     ESI.Type = EST_DependentNoexcept;
1632     Changed = true;
1633   }
1634   return inherited::TransformExceptionSpec(Loc, ESI, Exceptions, Changed);
1635 }
1636
1637 NamedDecl *
1638 TemplateInstantiator::TransformFirstQualifierInScope(NamedDecl *D,
1639                                                      SourceLocation Loc) {
1640   // If the first part of the nested-name-specifier was a template type
1641   // parameter, instantiate that type parameter down to a tag type.
1642   if (TemplateTypeParmDecl *TTPD = dyn_cast_or_null<TemplateTypeParmDecl>(D)) {
1643     const TemplateTypeParmType *TTP
1644       = cast<TemplateTypeParmType>(getSema().Context.getTypeDeclType(TTPD));
1645
1646     if (TTP->getDepth() < TemplateArgs.getNumLevels()) {
1647       // FIXME: This needs testing w/ member access expressions.
1648       TemplateArgument Arg = TemplateArgs(TTP->getDepth(), TTP->getIndex());
1649
1650       if (TTP->isParameterPack()) {
1651         assert(Arg.getKind() == TemplateArgument::Pack &&
1652                "Missing argument pack");
1653
1654         if (getSema().ArgumentPackSubstitutionIndex == -1)
1655           return nullptr;
1656
1657         Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
1658       }
1659
1660       QualType T = Arg.getAsType();
1661       if (T.isNull())
1662         return cast_or_null<NamedDecl>(TransformDecl(Loc, D));
1663
1664       if (const TagType *Tag = T->getAs<TagType>())
1665         return Tag->getDecl();
1666
1667       // The resulting type is not a tag; complain.
1668       getSema().Diag(Loc, diag::err_nested_name_spec_non_tag) << T;
1669       return nullptr;
1670     }
1671   }
1672
1673   return cast_or_null<NamedDecl>(TransformDecl(Loc, D));
1674 }
1675
1676 VarDecl *
1677 TemplateInstantiator::RebuildExceptionDecl(VarDecl *ExceptionDecl,
1678                                            TypeSourceInfo *Declarator,
1679                                            SourceLocation StartLoc,
1680                                            SourceLocation NameLoc,
1681                                            IdentifierInfo *Name) {
1682   VarDecl *Var = inherited::RebuildExceptionDecl(ExceptionDecl, Declarator,
1683                                                  StartLoc, NameLoc, Name);
1684   if (Var)
1685     getSema().CurrentInstantiationScope->InstantiatedLocal(ExceptionDecl, Var);
1686   return Var;
1687 }
1688
1689 VarDecl *TemplateInstantiator::RebuildObjCExceptionDecl(VarDecl *ExceptionDecl,
1690                                                         TypeSourceInfo *TSInfo,
1691                                                         QualType T) {
1692   VarDecl *Var = inherited::RebuildObjCExceptionDecl(ExceptionDecl, TSInfo, T);
1693   if (Var)
1694     getSema().CurrentInstantiationScope->InstantiatedLocal(ExceptionDecl, Var);
1695   return Var;
1696 }
1697
1698 QualType
1699 TemplateInstantiator::RebuildElaboratedType(SourceLocation KeywordLoc,
1700                                             ElaboratedTypeKeyword Keyword,
1701                                             NestedNameSpecifierLoc QualifierLoc,
1702                                             QualType T) {
1703   if (const TagType *TT = T->getAs<TagType>()) {
1704     TagDecl* TD = TT->getDecl();
1705
1706     SourceLocation TagLocation = KeywordLoc;
1707
1708     IdentifierInfo *Id = TD->getIdentifier();
1709
1710     // TODO: should we even warn on struct/class mismatches for this?  Seems
1711     // like it's likely to produce a lot of spurious errors.
1712     if (Id && Keyword != ElaboratedTypeKeyword::None &&
1713         Keyword != ElaboratedTypeKeyword::Typename) {
1714       TagTypeKind Kind = TypeWithKeyword::getTagTypeKindForKeyword(Keyword);
1715       if (!SemaRef.isAcceptableTagRedeclaration(TD, Kind, /*isDefinition*/false,
1716                                                 TagLocation, Id)) {
1717         SemaRef.Diag(TagLocation, diag::err_use_with_wrong_tag)
1718           << Id
1719           << FixItHint::CreateReplacement(SourceRange(TagLocation),
1720                                           TD->getKindName());
1721         SemaRef.Diag(TD->getLocation(), diag::note_previous_use);
1722       }
1723     }
1724   }
1725
1726   return inherited::RebuildElaboratedType(KeywordLoc, Keyword, QualifierLoc, T);
1727 }
1728
1729 TemplateName TemplateInstantiator::TransformTemplateName(
1730     CXXScopeSpec &SS, TemplateName Name, SourceLocation NameLoc,
1731     QualType ObjectType, NamedDecl *FirstQualifierInScope,
1732     bool AllowInjectedClassName) {
1733   if (TemplateTemplateParmDecl *TTP
1734        = dyn_cast_or_null<TemplateTemplateParmDecl>(Name.getAsTemplateDecl())) {
1735     if (TTP->getDepth() < TemplateArgs.getNumLevels()) {
1736       // If the corresponding template argument is NULL or non-existent, it's
1737       // because we are performing instantiation from explicitly-specified
1738       // template arguments in a function template, but there were some
1739       // arguments left unspecified.
1740       if (!TemplateArgs.hasTemplateArgument(TTP->getDepth(),
1741                                             TTP->getPosition()))
1742         return Name;
1743
1744       TemplateArgument Arg = TemplateArgs(TTP->getDepth(), TTP->getPosition());
1745
1746       if (TemplateArgs.isRewrite()) {
1747         // We're rewriting the template parameter as a reference to another
1748         // template parameter.
1749         if (Arg.getKind() == TemplateArgument::Pack) {
1750           assert(Arg.pack_size() == 1 && Arg.pack_begin()->isPackExpansion() &&
1751                  "unexpected pack arguments in template rewrite");
1752           Arg = Arg.pack_begin()->getPackExpansionPattern();
1753         }
1754         assert(Arg.getKind() == TemplateArgument::Template &&
1755                "unexpected nontype template argument kind in template rewrite");
1756         return Arg.getAsTemplate();
1757       }
1758
1759       auto [AssociatedDecl, Final] =
1760           TemplateArgs.getAssociatedDecl(TTP->getDepth());
1761       std::optional<unsigned> PackIndex;
1762       if (TTP->isParameterPack()) {
1763         assert(Arg.getKind() == TemplateArgument::Pack &&
1764                "Missing argument pack");
1765
1766         if (getSema().ArgumentPackSubstitutionIndex == -1) {
1767           // We have the template argument pack to substitute, but we're not
1768           // actually expanding the enclosing pack expansion yet. So, just
1769           // keep the entire argument pack.
1770           return getSema().Context.getSubstTemplateTemplateParmPack(
1771               Arg, AssociatedDecl, TTP->getIndex(), Final);
1772         }
1773
1774         PackIndex = getPackIndex(Arg);
1775         Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
1776       }
1777
1778       TemplateName Template = Arg.getAsTemplate().getNameToSubstitute();
1779       assert(!Template.isNull() && "Null template template argument");
1780       assert(!Template.getAsQualifiedTemplateName() &&
1781              "template decl to substitute is qualified?");
1782
1783       if (Final)
1784         return Template;
1785       return getSema().Context.getSubstTemplateTemplateParm(
1786           Template, AssociatedDecl, TTP->getIndex(), PackIndex);
1787     }
1788   }
1789
1790   if (SubstTemplateTemplateParmPackStorage *SubstPack
1791       = Name.getAsSubstTemplateTemplateParmPack()) {
1792     if (getSema().ArgumentPackSubstitutionIndex == -1)
1793       return Name;
1794
1795     TemplateArgument Pack = SubstPack->getArgumentPack();
1796     TemplateName Template =
1797         getPackSubstitutedTemplateArgument(getSema(), Pack).getAsTemplate();
1798     if (SubstPack->getFinal())
1799       return Template;
1800     return getSema().Context.getSubstTemplateTemplateParm(
1801         Template.getNameToSubstitute(), SubstPack->getAssociatedDecl(),
1802         SubstPack->getIndex(), getPackIndex(Pack));
1803   }
1804
1805   return inherited::TransformTemplateName(SS, Name, NameLoc, ObjectType,
1806                                           FirstQualifierInScope,
1807                                           AllowInjectedClassName);
1808 }
1809
1810 ExprResult
1811 TemplateInstantiator::TransformPredefinedExpr(PredefinedExpr *E) {
1812   if (!E->isTypeDependent())
1813     return E;
1814
1815   return getSema().BuildPredefinedExpr(E->getLocation(), E->getIdentKind());
1816 }
1817
1818 ExprResult
1819 TemplateInstantiator::TransformTemplateParmRefExpr(DeclRefExpr *E,
1820                                                NonTypeTemplateParmDecl *NTTP) {
1821   // If the corresponding template argument is NULL or non-existent, it's
1822   // because we are performing instantiation from explicitly-specified
1823   // template arguments in a function template, but there were some
1824   // arguments left unspecified.
1825   if (!TemplateArgs.hasTemplateArgument(NTTP->getDepth(),
1826                                         NTTP->getPosition()))
1827     return E;
1828
1829   TemplateArgument Arg = TemplateArgs(NTTP->getDepth(), NTTP->getPosition());
1830
1831   if (TemplateArgs.isRewrite()) {
1832     // We're rewriting the template parameter as a reference to another
1833     // template parameter.
1834     if (Arg.getKind() == TemplateArgument::Pack) {
1835       assert(Arg.pack_size() == 1 && Arg.pack_begin()->isPackExpansion() &&
1836              "unexpected pack arguments in template rewrite");
1837       Arg = Arg.pack_begin()->getPackExpansionPattern();
1838     }
1839     assert(Arg.getKind() == TemplateArgument::Expression &&
1840            "unexpected nontype template argument kind in template rewrite");
1841     // FIXME: This can lead to the same subexpression appearing multiple times
1842     // in a complete expression.
1843     return Arg.getAsExpr();
1844   }
1845
1846   auto [AssociatedDecl, _] = TemplateArgs.getAssociatedDecl(NTTP->getDepth());
1847   std::optional<unsigned> PackIndex;
1848   if (NTTP->isParameterPack()) {
1849     assert(Arg.getKind() == TemplateArgument::Pack &&
1850            "Missing argument pack");
1851
1852     if (getSema().ArgumentPackSubstitutionIndex == -1) {
1853       // We have an argument pack, but we can't select a particular argument
1854       // out of it yet. Therefore, we'll build an expression to hold on to that
1855       // argument pack.
1856       QualType TargetType = SemaRef.SubstType(NTTP->getType(), TemplateArgs,
1857                                               E->getLocation(),
1858                                               NTTP->getDeclName());
1859       if (TargetType.isNull())
1860         return ExprError();
1861
1862       QualType ExprType = TargetType.getNonLValueExprType(SemaRef.Context);
1863       if (TargetType->isRecordType())
1864         ExprType.addConst();
1865       // FIXME: Pass in Final.
1866       return new (SemaRef.Context) SubstNonTypeTemplateParmPackExpr(
1867           ExprType, TargetType->isReferenceType() ? VK_LValue : VK_PRValue,
1868           E->getLocation(), Arg, AssociatedDecl, NTTP->getPosition());
1869     }
1870     PackIndex = getPackIndex(Arg);
1871     Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
1872   }
1873   // FIXME: Don't put subst node on Final replacement.
1874   return transformNonTypeTemplateParmRef(AssociatedDecl, NTTP, E->getLocation(),
1875                                          Arg, PackIndex);
1876 }
1877
1878 const LoopHintAttr *
1879 TemplateInstantiator::TransformLoopHintAttr(const LoopHintAttr *LH) {
1880   Expr *TransformedExpr = getDerived().TransformExpr(LH->getValue()).get();
1881
1882   if (TransformedExpr == LH->getValue())
1883     return LH;
1884
1885   // Generate error if there is a problem with the value.
1886   if (getSema().CheckLoopHintExpr(TransformedExpr, LH->getLocation()))
1887     return LH;
1888
1889   // Create new LoopHintValueAttr with integral expression in place of the
1890   // non-type template parameter.
1891   return LoopHintAttr::CreateImplicit(getSema().Context, LH->getOption(),
1892                                       LH->getState(), TransformedExpr, *LH);
1893 }
1894 const NoInlineAttr *TemplateInstantiator::TransformStmtNoInlineAttr(
1895     const Stmt *OrigS, const Stmt *InstS, const NoInlineAttr *A) {
1896   if (!A || getSema().CheckNoInlineAttr(OrigS, InstS, *A))
1897     return nullptr;
1898
1899   return A;
1900 }
1901 const AlwaysInlineAttr *TemplateInstantiator::TransformStmtAlwaysInlineAttr(
1902     const Stmt *OrigS, const Stmt *InstS, const AlwaysInlineAttr *A) {
1903   if (!A || getSema().CheckAlwaysInlineAttr(OrigS, InstS, *A))
1904     return nullptr;
1905
1906   return A;
1907 }
1908
1909 ExprResult TemplateInstantiator::transformNonTypeTemplateParmRef(
1910     Decl *AssociatedDecl, const NonTypeTemplateParmDecl *parm,
1911     SourceLocation loc, TemplateArgument arg,
1912     std::optional<unsigned> PackIndex) {
1913   ExprResult result;
1914
1915   // Determine the substituted parameter type. We can usually infer this from
1916   // the template argument, but not always.
1917   auto SubstParamType = [&] {
1918     QualType T;
1919     if (parm->isExpandedParameterPack())
1920       T = parm->getExpansionType(SemaRef.ArgumentPackSubstitutionIndex);
1921     else
1922       T = parm->getType();
1923     if (parm->isParameterPack() && isa<PackExpansionType>(T))
1924       T = cast<PackExpansionType>(T)->getPattern();
1925     return SemaRef.SubstType(T, TemplateArgs, loc, parm->getDeclName());
1926   };
1927
1928   bool refParam = false;
1929
1930   // The template argument itself might be an expression, in which case we just
1931   // return that expression. This happens when substituting into an alias
1932   // template.
1933   if (arg.getKind() == TemplateArgument::Expression) {
1934     Expr *argExpr = arg.getAsExpr();
1935     result = argExpr;
1936     if (argExpr->isLValue()) {
1937       if (argExpr->getType()->isRecordType()) {
1938         // Check whether the parameter was actually a reference.
1939         QualType paramType = SubstParamType();
1940         if (paramType.isNull())
1941           return ExprError();
1942         refParam = paramType->isReferenceType();
1943       } else {
1944         refParam = true;
1945       }
1946     }
1947   } else if (arg.getKind() == TemplateArgument::Declaration ||
1948              arg.getKind() == TemplateArgument::NullPtr) {
1949     ValueDecl *VD;
1950     if (arg.getKind() == TemplateArgument::Declaration) {
1951       VD = arg.getAsDecl();
1952
1953       // Find the instantiation of the template argument.  This is
1954       // required for nested templates.
1955       VD = cast_or_null<ValueDecl>(
1956              getSema().FindInstantiatedDecl(loc, VD, TemplateArgs));
1957       if (!VD)
1958         return ExprError();
1959     } else {
1960       // Propagate NULL template argument.
1961       VD = nullptr;
1962     }
1963
1964     QualType paramType = VD ? arg.getParamTypeForDecl() : arg.getNullPtrType();
1965     assert(!paramType.isNull() && "type substitution failed for param type");
1966     assert(!paramType->isDependentType() && "param type still dependent");
1967     result = SemaRef.BuildExpressionFromDeclTemplateArgument(arg, paramType, loc);
1968     refParam = paramType->isReferenceType();
1969   } else {
1970     result = SemaRef.BuildExpressionFromIntegralTemplateArgument(arg, loc);
1971     assert(result.isInvalid() ||
1972            SemaRef.Context.hasSameType(result.get()->getType(),
1973                                        arg.getIntegralType()));
1974   }
1975
1976   if (result.isInvalid())
1977     return ExprError();
1978
1979   Expr *resultExpr = result.get();
1980   // FIXME: Don't put subst node on final replacement.
1981   return new (SemaRef.Context) SubstNonTypeTemplateParmExpr(
1982       resultExpr->getType(), resultExpr->getValueKind(), loc, resultExpr,
1983       AssociatedDecl, parm->getIndex(), PackIndex, refParam);
1984 }
1985
1986 ExprResult
1987 TemplateInstantiator::TransformSubstNonTypeTemplateParmPackExpr(
1988                                           SubstNonTypeTemplateParmPackExpr *E) {
1989   if (getSema().ArgumentPackSubstitutionIndex == -1) {
1990     // We aren't expanding the parameter pack, so just return ourselves.
1991     return E;
1992   }
1993
1994   TemplateArgument Pack = E->getArgumentPack();
1995   TemplateArgument Arg = getPackSubstitutedTemplateArgument(getSema(), Pack);
1996   // FIXME: Don't put subst node on final replacement.
1997   return transformNonTypeTemplateParmRef(
1998       E->getAssociatedDecl(), E->getParameterPack(),
1999       E->getParameterPackLocation(), Arg, getPackIndex(Pack));
2000 }
2001
2002 ExprResult
2003 TemplateInstantiator::TransformSubstNonTypeTemplateParmExpr(
2004                                           SubstNonTypeTemplateParmExpr *E) {
2005   ExprResult SubstReplacement = E->getReplacement();
2006   if (!isa<ConstantExpr>(SubstReplacement.get()))
2007     SubstReplacement = TransformExpr(E->getReplacement());
2008   if (SubstReplacement.isInvalid())
2009     return true;
2010   QualType SubstType = TransformType(E->getParameterType(getSema().Context));
2011   if (SubstType.isNull())
2012     return true;
2013   // The type may have been previously dependent and not now, which means we
2014   // might have to implicit cast the argument to the new type, for example:
2015   // template<auto T, decltype(T) U>
2016   // concept C = sizeof(U) == 4;
2017   // void foo() requires C<2, 'a'> { }
2018   // When normalizing foo(), we first form the normalized constraints of C:
2019   // AtomicExpr(sizeof(U) == 4,
2020   //            U=SubstNonTypeTemplateParmExpr(Param=U,
2021   //                                           Expr=DeclRef(U),
2022   //                                           Type=decltype(T)))
2023   // Then we substitute T = 2, U = 'a' into the parameter mapping, and need to
2024   // produce:
2025   // AtomicExpr(sizeof(U) == 4,
2026   //            U=SubstNonTypeTemplateParmExpr(Param=U,
2027   //                                           Expr=ImpCast(
2028   //                                               decltype(2),
2029   //                                               SubstNTTPE(Param=U, Expr='a',
2030   //                                                          Type=char)),
2031   //                                           Type=decltype(2)))
2032   // The call to CheckTemplateArgument here produces the ImpCast.
2033   TemplateArgument SugaredConverted, CanonicalConverted;
2034   if (SemaRef
2035           .CheckTemplateArgument(E->getParameter(), SubstType,
2036                                  SubstReplacement.get(), SugaredConverted,
2037                                  CanonicalConverted, Sema::CTAK_Specified)
2038           .isInvalid())
2039     return true;
2040   return transformNonTypeTemplateParmRef(E->getAssociatedDecl(),
2041                                          E->getParameter(), E->getExprLoc(),
2042                                          SugaredConverted, E->getPackIndex());
2043 }
2044
2045 ExprResult TemplateInstantiator::RebuildVarDeclRefExpr(VarDecl *PD,
2046                                                        SourceLocation Loc) {
2047   DeclarationNameInfo NameInfo(PD->getDeclName(), Loc);
2048   return getSema().BuildDeclarationNameExpr(CXXScopeSpec(), NameInfo, PD);
2049 }
2050
2051 ExprResult
2052 TemplateInstantiator::TransformFunctionParmPackExpr(FunctionParmPackExpr *E) {
2053   if (getSema().ArgumentPackSubstitutionIndex != -1) {
2054     // We can expand this parameter pack now.
2055     VarDecl *D = E->getExpansion(getSema().ArgumentPackSubstitutionIndex);
2056     VarDecl *VD = cast_or_null<VarDecl>(TransformDecl(E->getExprLoc(), D));
2057     if (!VD)
2058       return ExprError();
2059     return RebuildVarDeclRefExpr(VD, E->getExprLoc());
2060   }
2061
2062   QualType T = TransformType(E->getType());
2063   if (T.isNull())
2064     return ExprError();
2065
2066   // Transform each of the parameter expansions into the corresponding
2067   // parameters in the instantiation of the function decl.
2068   SmallVector<VarDecl *, 8> Vars;
2069   Vars.reserve(E->getNumExpansions());
2070   for (FunctionParmPackExpr::iterator I = E->begin(), End = E->end();
2071        I != End; ++I) {
2072     VarDecl *D = cast_or_null<VarDecl>(TransformDecl(E->getExprLoc(), *I));
2073     if (!D)
2074       return ExprError();
2075     Vars.push_back(D);
2076   }
2077
2078   auto *PackExpr =
2079       FunctionParmPackExpr::Create(getSema().Context, T, E->getParameterPack(),
2080                                    E->getParameterPackLocation(), Vars);
2081   getSema().MarkFunctionParmPackReferenced(PackExpr);
2082   return PackExpr;
2083 }
2084
2085 ExprResult
2086 TemplateInstantiator::TransformFunctionParmPackRefExpr(DeclRefExpr *E,
2087                                                        VarDecl *PD) {
2088   typedef LocalInstantiationScope::DeclArgumentPack DeclArgumentPack;
2089   llvm::PointerUnion<Decl *, DeclArgumentPack *> *Found
2090     = getSema().CurrentInstantiationScope->findInstantiationOf(PD);
2091   assert(Found && "no instantiation for parameter pack");
2092
2093   Decl *TransformedDecl;
2094   if (DeclArgumentPack *Pack = Found->dyn_cast<DeclArgumentPack *>()) {
2095     // If this is a reference to a function parameter pack which we can
2096     // substitute but can't yet expand, build a FunctionParmPackExpr for it.
2097     if (getSema().ArgumentPackSubstitutionIndex == -1) {
2098       QualType T = TransformType(E->getType());
2099       if (T.isNull())
2100         return ExprError();
2101       auto *PackExpr = FunctionParmPackExpr::Create(getSema().Context, T, PD,
2102                                                     E->getExprLoc(), *Pack);
2103       getSema().MarkFunctionParmPackReferenced(PackExpr);
2104       return PackExpr;
2105     }
2106
2107     TransformedDecl = (*Pack)[getSema().ArgumentPackSubstitutionIndex];
2108   } else {
2109     TransformedDecl = Found->get<Decl*>();
2110   }
2111
2112   // We have either an unexpanded pack or a specific expansion.
2113   return RebuildVarDeclRefExpr(cast<VarDecl>(TransformedDecl), E->getExprLoc());
2114 }
2115
2116 ExprResult
2117 TemplateInstantiator::TransformDeclRefExpr(DeclRefExpr *E) {
2118   NamedDecl *D = E->getDecl();
2119
2120   // Handle references to non-type template parameters and non-type template
2121   // parameter packs.
2122   if (NonTypeTemplateParmDecl *NTTP = dyn_cast<NonTypeTemplateParmDecl>(D)) {
2123     if (NTTP->getDepth() < TemplateArgs.getNumLevels())
2124       return TransformTemplateParmRefExpr(E, NTTP);
2125
2126     // We have a non-type template parameter that isn't fully substituted;
2127     // FindInstantiatedDecl will find it in the local instantiation scope.
2128   }
2129
2130   // Handle references to function parameter packs.
2131   if (VarDecl *PD = dyn_cast<VarDecl>(D))
2132     if (PD->isParameterPack())
2133       return TransformFunctionParmPackRefExpr(E, PD);
2134
2135   return inherited::TransformDeclRefExpr(E);
2136 }
2137
2138 ExprResult TemplateInstantiator::TransformCXXDefaultArgExpr(
2139     CXXDefaultArgExpr *E) {
2140   assert(!cast<FunctionDecl>(E->getParam()->getDeclContext())->
2141              getDescribedFunctionTemplate() &&
2142          "Default arg expressions are never formed in dependent cases.");
2143   return SemaRef.BuildCXXDefaultArgExpr(
2144       E->getUsedLocation(), cast<FunctionDecl>(E->getParam()->getDeclContext()),
2145       E->getParam());
2146 }
2147
2148 template<typename Fn>
2149 QualType TemplateInstantiator::TransformFunctionProtoType(TypeLocBuilder &TLB,
2150                                  FunctionProtoTypeLoc TL,
2151                                  CXXRecordDecl *ThisContext,
2152                                  Qualifiers ThisTypeQuals,
2153                                  Fn TransformExceptionSpec) {
2154   // We need a local instantiation scope for this function prototype.
2155   LocalInstantiationScope Scope(SemaRef, /*CombineWithOuterScope=*/true);
2156   return inherited::TransformFunctionProtoType(
2157       TLB, TL, ThisContext, ThisTypeQuals, TransformExceptionSpec);
2158 }
2159
2160 ParmVarDecl *TemplateInstantiator::TransformFunctionTypeParam(
2161     ParmVarDecl *OldParm, int indexAdjustment,
2162     std::optional<unsigned> NumExpansions, bool ExpectParameterPack) {
2163   auto NewParm = SemaRef.SubstParmVarDecl(
2164       OldParm, TemplateArgs, indexAdjustment, NumExpansions,
2165       ExpectParameterPack, EvaluateConstraints);
2166   if (NewParm && SemaRef.getLangOpts().OpenCL)
2167     SemaRef.deduceOpenCLAddressSpace(NewParm);
2168   return NewParm;
2169 }
2170
2171 QualType TemplateInstantiator::BuildSubstTemplateTypeParmType(
2172     TypeLocBuilder &TLB, bool SuppressObjCLifetime, bool Final,
2173     Decl *AssociatedDecl, unsigned Index, std::optional<unsigned> PackIndex,
2174     TemplateArgument Arg, SourceLocation NameLoc) {
2175   QualType Replacement = Arg.getAsType();
2176
2177   // If the template parameter had ObjC lifetime qualifiers,
2178   // then any such qualifiers on the replacement type are ignored.
2179   if (SuppressObjCLifetime) {
2180     Qualifiers RQs;
2181     RQs = Replacement.getQualifiers();
2182     RQs.removeObjCLifetime();
2183     Replacement =
2184         SemaRef.Context.getQualifiedType(Replacement.getUnqualifiedType(), RQs);
2185   }
2186
2187   if (Final) {
2188     TLB.pushTrivial(SemaRef.Context, Replacement, NameLoc);
2189     return Replacement;
2190   }
2191   // TODO: only do this uniquing once, at the start of instantiation.
2192   QualType Result = getSema().Context.getSubstTemplateTypeParmType(
2193       Replacement, AssociatedDecl, Index, PackIndex);
2194   SubstTemplateTypeParmTypeLoc NewTL =
2195       TLB.push<SubstTemplateTypeParmTypeLoc>(Result);
2196   NewTL.setNameLoc(NameLoc);
2197   return Result;
2198 }
2199
2200 QualType
2201 TemplateInstantiator::TransformTemplateTypeParmType(TypeLocBuilder &TLB,
2202                                                     TemplateTypeParmTypeLoc TL,
2203                                                     bool SuppressObjCLifetime) {
2204   const TemplateTypeParmType *T = TL.getTypePtr();
2205   if (T->getDepth() < TemplateArgs.getNumLevels()) {
2206     // Replace the template type parameter with its corresponding
2207     // template argument.
2208
2209     // If the corresponding template argument is NULL or doesn't exist, it's
2210     // because we are performing instantiation from explicitly-specified
2211     // template arguments in a function template class, but there were some
2212     // arguments left unspecified.
2213     if (!TemplateArgs.hasTemplateArgument(T->getDepth(), T->getIndex())) {
2214       TemplateTypeParmTypeLoc NewTL
2215         = TLB.push<TemplateTypeParmTypeLoc>(TL.getType());
2216       NewTL.setNameLoc(TL.getNameLoc());
2217       return TL.getType();
2218     }
2219
2220     TemplateArgument Arg = TemplateArgs(T->getDepth(), T->getIndex());
2221
2222     if (TemplateArgs.isRewrite()) {
2223       // We're rewriting the template parameter as a reference to another
2224       // template parameter.
2225       if (Arg.getKind() == TemplateArgument::Pack) {
2226         assert(Arg.pack_size() == 1 && Arg.pack_begin()->isPackExpansion() &&
2227                "unexpected pack arguments in template rewrite");
2228         Arg = Arg.pack_begin()->getPackExpansionPattern();
2229       }
2230       assert(Arg.getKind() == TemplateArgument::Type &&
2231              "unexpected nontype template argument kind in template rewrite");
2232       QualType NewT = Arg.getAsType();
2233       assert(isa<TemplateTypeParmType>(NewT) &&
2234              "type parm not rewritten to type parm");
2235       auto NewTL = TLB.push<TemplateTypeParmTypeLoc>(NewT);
2236       NewTL.setNameLoc(TL.getNameLoc());
2237       return NewT;
2238     }
2239
2240     auto [AssociatedDecl, Final] =
2241         TemplateArgs.getAssociatedDecl(T->getDepth());
2242     std::optional<unsigned> PackIndex;
2243     if (T->isParameterPack()) {
2244       assert(Arg.getKind() == TemplateArgument::Pack &&
2245              "Missing argument pack");
2246
2247       if (getSema().ArgumentPackSubstitutionIndex == -1) {
2248         // We have the template argument pack, but we're not expanding the
2249         // enclosing pack expansion yet. Just save the template argument
2250         // pack for later substitution.
2251         QualType Result = getSema().Context.getSubstTemplateTypeParmPackType(
2252             AssociatedDecl, T->getIndex(), Final, Arg);
2253         SubstTemplateTypeParmPackTypeLoc NewTL
2254           = TLB.push<SubstTemplateTypeParmPackTypeLoc>(Result);
2255         NewTL.setNameLoc(TL.getNameLoc());
2256         return Result;
2257       }
2258
2259       // PackIndex starts from last element.
2260       PackIndex = getPackIndex(Arg);
2261       Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
2262     }
2263
2264     assert(Arg.getKind() == TemplateArgument::Type &&
2265            "Template argument kind mismatch");
2266
2267     return BuildSubstTemplateTypeParmType(TLB, SuppressObjCLifetime, Final,
2268                                           AssociatedDecl, T->getIndex(),
2269                                           PackIndex, Arg, TL.getNameLoc());
2270   }
2271
2272   // The template type parameter comes from an inner template (e.g.,
2273   // the template parameter list of a member template inside the
2274   // template we are instantiating). Create a new template type
2275   // parameter with the template "level" reduced by one.
2276   TemplateTypeParmDecl *NewTTPDecl = nullptr;
2277   if (TemplateTypeParmDecl *OldTTPDecl = T->getDecl())
2278     NewTTPDecl = cast_or_null<TemplateTypeParmDecl>(
2279         TransformDecl(TL.getNameLoc(), OldTTPDecl));
2280   QualType Result = getSema().Context.getTemplateTypeParmType(
2281       T->getDepth() - TemplateArgs.getNumSubstitutedLevels(), T->getIndex(),
2282       T->isParameterPack(), NewTTPDecl);
2283   TemplateTypeParmTypeLoc NewTL = TLB.push<TemplateTypeParmTypeLoc>(Result);
2284   NewTL.setNameLoc(TL.getNameLoc());
2285   return Result;
2286 }
2287
2288 QualType TemplateInstantiator::TransformSubstTemplateTypeParmPackType(
2289     TypeLocBuilder &TLB, SubstTemplateTypeParmPackTypeLoc TL,
2290     bool SuppressObjCLifetime) {
2291   const SubstTemplateTypeParmPackType *T = TL.getTypePtr();
2292
2293   Decl *NewReplaced = TransformDecl(TL.getNameLoc(), T->getAssociatedDecl());
2294
2295   if (getSema().ArgumentPackSubstitutionIndex == -1) {
2296     // We aren't expanding the parameter pack, so just return ourselves.
2297     QualType Result = TL.getType();
2298     if (NewReplaced != T->getAssociatedDecl())
2299       Result = getSema().Context.getSubstTemplateTypeParmPackType(
2300           NewReplaced, T->getIndex(), T->getFinal(), T->getArgumentPack());
2301     SubstTemplateTypeParmPackTypeLoc NewTL =
2302         TLB.push<SubstTemplateTypeParmPackTypeLoc>(Result);
2303     NewTL.setNameLoc(TL.getNameLoc());
2304     return Result;
2305   }
2306
2307   TemplateArgument Pack = T->getArgumentPack();
2308   TemplateArgument Arg = getPackSubstitutedTemplateArgument(getSema(), Pack);
2309   return BuildSubstTemplateTypeParmType(
2310       TLB, SuppressObjCLifetime, T->getFinal(), NewReplaced, T->getIndex(),
2311       getPackIndex(Pack), Arg, TL.getNameLoc());
2312 }
2313
2314 static concepts::Requirement::SubstitutionDiagnostic *
2315 createSubstDiag(Sema &S, TemplateDeductionInfo &Info,
2316                 concepts::EntityPrinter Printer) {
2317   SmallString<128> Message;
2318   SourceLocation ErrorLoc;
2319   if (Info.hasSFINAEDiagnostic()) {
2320     PartialDiagnosticAt PDA(SourceLocation(),
2321                             PartialDiagnostic::NullDiagnostic{});
2322     Info.takeSFINAEDiagnostic(PDA);
2323     PDA.second.EmitToString(S.getDiagnostics(), Message);
2324     ErrorLoc = PDA.first;
2325   } else {
2326     ErrorLoc = Info.getLocation();
2327   }
2328   char *MessageBuf = new (S.Context) char[Message.size()];
2329   std::copy(Message.begin(), Message.end(), MessageBuf);
2330   SmallString<128> Entity;
2331   llvm::raw_svector_ostream OS(Entity);
2332   Printer(OS);
2333   char *EntityBuf = new (S.Context) char[Entity.size()];
2334   std::copy(Entity.begin(), Entity.end(), EntityBuf);
2335   return new (S.Context) concepts::Requirement::SubstitutionDiagnostic{
2336       StringRef(EntityBuf, Entity.size()), ErrorLoc,
2337       StringRef(MessageBuf, Message.size())};
2338 }
2339
2340 concepts::Requirement::SubstitutionDiagnostic *
2341 concepts::createSubstDiagAt(Sema &S, SourceLocation Location,
2342                             EntityPrinter Printer) {
2343   SmallString<128> Entity;
2344   llvm::raw_svector_ostream OS(Entity);
2345   Printer(OS);
2346   char *EntityBuf = new (S.Context) char[Entity.size()];
2347   llvm::copy(Entity, EntityBuf);
2348   return new (S.Context) concepts::Requirement::SubstitutionDiagnostic{
2349       /*SubstitutedEntity=*/StringRef(EntityBuf, Entity.size()),
2350       /*DiagLoc=*/Location, /*DiagMessage=*/StringRef()};
2351 }
2352
2353 ExprResult TemplateInstantiator::TransformRequiresTypeParams(
2354     SourceLocation KWLoc, SourceLocation RBraceLoc, const RequiresExpr *RE,
2355     RequiresExprBodyDecl *Body, ArrayRef<ParmVarDecl *> Params,
2356     SmallVectorImpl<QualType> &PTypes,
2357     SmallVectorImpl<ParmVarDecl *> &TransParams,
2358     Sema::ExtParameterInfoBuilder &PInfos) {
2359
2360   TemplateDeductionInfo Info(KWLoc);
2361   Sema::InstantiatingTemplate TypeInst(SemaRef, KWLoc,
2362                                        RE, Info,
2363                                        SourceRange{KWLoc, RBraceLoc});
2364   Sema::SFINAETrap Trap(SemaRef);
2365
2366   unsigned ErrorIdx;
2367   if (getDerived().TransformFunctionTypeParams(
2368           KWLoc, Params, /*ParamTypes=*/nullptr, /*ParamInfos=*/nullptr, PTypes,
2369           &TransParams, PInfos, &ErrorIdx) ||
2370       Trap.hasErrorOccurred()) {
2371     SmallVector<concepts::Requirement *, 4> TransReqs;
2372     ParmVarDecl *FailedDecl = Params[ErrorIdx];
2373     // Add a 'failed' Requirement to contain the error that caused the failure
2374     // here.
2375     TransReqs.push_back(RebuildTypeRequirement(createSubstDiag(
2376         SemaRef, Info, [&](llvm::raw_ostream &OS) { OS << *FailedDecl; })));
2377     return getDerived().RebuildRequiresExpr(KWLoc, Body, RE->getLParenLoc(),
2378                                             TransParams, RE->getRParenLoc(),
2379                                             TransReqs, RBraceLoc);
2380   }
2381
2382   return ExprResult{};
2383 }
2384
2385 concepts::TypeRequirement *
2386 TemplateInstantiator::TransformTypeRequirement(concepts::TypeRequirement *Req) {
2387   if (!Req->isDependent() && !AlwaysRebuild())
2388     return Req;
2389   if (Req->isSubstitutionFailure()) {
2390     if (AlwaysRebuild())
2391       return RebuildTypeRequirement(
2392               Req->getSubstitutionDiagnostic());
2393     return Req;
2394   }
2395
2396   Sema::SFINAETrap Trap(SemaRef);
2397   TemplateDeductionInfo Info(Req->getType()->getTypeLoc().getBeginLoc());
2398   Sema::InstantiatingTemplate TypeInst(SemaRef,
2399       Req->getType()->getTypeLoc().getBeginLoc(), Req, Info,
2400       Req->getType()->getTypeLoc().getSourceRange());
2401   if (TypeInst.isInvalid())
2402     return nullptr;
2403   TypeSourceInfo *TransType = TransformType(Req->getType());
2404   if (!TransType || Trap.hasErrorOccurred())
2405     return RebuildTypeRequirement(createSubstDiag(SemaRef, Info,
2406         [&] (llvm::raw_ostream& OS) {
2407             Req->getType()->getType().print(OS, SemaRef.getPrintingPolicy());
2408         }));
2409   return RebuildTypeRequirement(TransType);
2410 }
2411
2412 concepts::ExprRequirement *
2413 TemplateInstantiator::TransformExprRequirement(concepts::ExprRequirement *Req) {
2414   if (!Req->isDependent() && !AlwaysRebuild())
2415     return Req;
2416
2417   Sema::SFINAETrap Trap(SemaRef);
2418
2419   llvm::PointerUnion<Expr *, concepts::Requirement::SubstitutionDiagnostic *>
2420       TransExpr;
2421   if (Req->isExprSubstitutionFailure())
2422     TransExpr = Req->getExprSubstitutionDiagnostic();
2423   else {
2424     Expr *E = Req->getExpr();
2425     TemplateDeductionInfo Info(E->getBeginLoc());
2426     Sema::InstantiatingTemplate ExprInst(SemaRef, E->getBeginLoc(), Req, Info,
2427                                          E->getSourceRange());
2428     if (ExprInst.isInvalid())
2429       return nullptr;
2430     ExprResult TransExprRes = TransformExpr(E);
2431     if (!TransExprRes.isInvalid() && !Trap.hasErrorOccurred() &&
2432         TransExprRes.get()->hasPlaceholderType())
2433       TransExprRes = SemaRef.CheckPlaceholderExpr(TransExprRes.get());
2434     if (TransExprRes.isInvalid() || Trap.hasErrorOccurred())
2435       TransExpr = createSubstDiag(SemaRef, Info, [&](llvm::raw_ostream &OS) {
2436         E->printPretty(OS, nullptr, SemaRef.getPrintingPolicy());
2437       });
2438     else
2439       TransExpr = TransExprRes.get();
2440   }
2441
2442   std::optional<concepts::ExprRequirement::ReturnTypeRequirement> TransRetReq;
2443   const auto &RetReq = Req->getReturnTypeRequirement();
2444   if (RetReq.isEmpty())
2445     TransRetReq.emplace();
2446   else if (RetReq.isSubstitutionFailure())
2447     TransRetReq.emplace(RetReq.getSubstitutionDiagnostic());
2448   else if (RetReq.isTypeConstraint()) {
2449     TemplateParameterList *OrigTPL =
2450         RetReq.getTypeConstraintTemplateParameterList();
2451     TemplateDeductionInfo Info(OrigTPL->getTemplateLoc());
2452     Sema::InstantiatingTemplate TPLInst(SemaRef, OrigTPL->getTemplateLoc(),
2453                                         Req, Info, OrigTPL->getSourceRange());
2454     if (TPLInst.isInvalid())
2455       return nullptr;
2456     TemplateParameterList *TPL = TransformTemplateParameterList(OrigTPL);
2457     if (!TPL)
2458       TransRetReq.emplace(createSubstDiag(SemaRef, Info,
2459           [&] (llvm::raw_ostream& OS) {
2460               RetReq.getTypeConstraint()->getImmediatelyDeclaredConstraint()
2461                   ->printPretty(OS, nullptr, SemaRef.getPrintingPolicy());
2462           }));
2463     else {
2464       TPLInst.Clear();
2465       TransRetReq.emplace(TPL);
2466     }
2467   }
2468   assert(TransRetReq && "All code paths leading here must set TransRetReq");
2469   if (Expr *E = TransExpr.dyn_cast<Expr *>())
2470     return RebuildExprRequirement(E, Req->isSimple(), Req->getNoexceptLoc(),
2471                                   std::move(*TransRetReq));
2472   return RebuildExprRequirement(
2473       TransExpr.get<concepts::Requirement::SubstitutionDiagnostic *>(),
2474       Req->isSimple(), Req->getNoexceptLoc(), std::move(*TransRetReq));
2475 }
2476
2477 concepts::NestedRequirement *
2478 TemplateInstantiator::TransformNestedRequirement(
2479     concepts::NestedRequirement *Req) {
2480   if (!Req->isDependent() && !AlwaysRebuild())
2481     return Req;
2482   if (Req->hasInvalidConstraint()) {
2483     if (AlwaysRebuild())
2484       return RebuildNestedRequirement(Req->getInvalidConstraintEntity(),
2485                                       Req->getConstraintSatisfaction());
2486     return Req;
2487   }
2488   Sema::InstantiatingTemplate ReqInst(SemaRef,
2489       Req->getConstraintExpr()->getBeginLoc(), Req,
2490       Sema::InstantiatingTemplate::ConstraintsCheck{},
2491       Req->getConstraintExpr()->getSourceRange());
2492
2493   ExprResult TransConstraint;
2494   ConstraintSatisfaction Satisfaction;
2495   TemplateDeductionInfo Info(Req->getConstraintExpr()->getBeginLoc());
2496   {
2497     EnterExpressionEvaluationContext ContextRAII(
2498         SemaRef, Sema::ExpressionEvaluationContext::ConstantEvaluated);
2499     Sema::SFINAETrap Trap(SemaRef);
2500     Sema::InstantiatingTemplate ConstrInst(SemaRef,
2501         Req->getConstraintExpr()->getBeginLoc(), Req, Info,
2502         Req->getConstraintExpr()->getSourceRange());
2503     if (ConstrInst.isInvalid())
2504       return nullptr;
2505     llvm::SmallVector<Expr *> Result;
2506     if (!SemaRef.CheckConstraintSatisfaction(
2507             nullptr, {Req->getConstraintExpr()}, Result, TemplateArgs,
2508             Req->getConstraintExpr()->getSourceRange(), Satisfaction) &&
2509         !Result.empty())
2510       TransConstraint = Result[0];
2511     assert(!Trap.hasErrorOccurred() && "Substitution failures must be handled "
2512                                        "by CheckConstraintSatisfaction.");
2513   }
2514   if (TransConstraint.isUsable() &&
2515       TransConstraint.get()->isInstantiationDependent())
2516     return new (SemaRef.Context)
2517         concepts::NestedRequirement(TransConstraint.get());
2518   if (TransConstraint.isInvalid() || !TransConstraint.get() ||
2519       Satisfaction.HasSubstitutionFailure()) {
2520     SmallString<128> Entity;
2521     llvm::raw_svector_ostream OS(Entity);
2522     Req->getConstraintExpr()->printPretty(OS, nullptr,
2523                                           SemaRef.getPrintingPolicy());
2524     char *EntityBuf = new (SemaRef.Context) char[Entity.size()];
2525     std::copy(Entity.begin(), Entity.end(), EntityBuf);
2526     return new (SemaRef.Context) concepts::NestedRequirement(
2527         SemaRef.Context, StringRef(EntityBuf, Entity.size()), Satisfaction);
2528   }
2529   return new (SemaRef.Context) concepts::NestedRequirement(
2530       SemaRef.Context, TransConstraint.get(), Satisfaction);
2531 }
2532
2533
2534 /// Perform substitution on the type T with a given set of template
2535 /// arguments.
2536 ///
2537 /// This routine substitutes the given template arguments into the
2538 /// type T and produces the instantiated type.
2539 ///
2540 /// \param T the type into which the template arguments will be
2541 /// substituted. If this type is not dependent, it will be returned
2542 /// immediately.
2543 ///
2544 /// \param Args the template arguments that will be
2545 /// substituted for the top-level template parameters within T.
2546 ///
2547 /// \param Loc the location in the source code where this substitution
2548 /// is being performed. It will typically be the location of the
2549 /// declarator (if we're instantiating the type of some declaration)
2550 /// or the location of the type in the source code (if, e.g., we're
2551 /// instantiating the type of a cast expression).
2552 ///
2553 /// \param Entity the name of the entity associated with a declaration
2554 /// being instantiated (if any). May be empty to indicate that there
2555 /// is no such entity (if, e.g., this is a type that occurs as part of
2556 /// a cast expression) or that the entity has no name (e.g., an
2557 /// unnamed function parameter).
2558 ///
2559 /// \param AllowDeducedTST Whether a DeducedTemplateSpecializationType is
2560 /// acceptable as the top level type of the result.
2561 ///
2562 /// \returns If the instantiation succeeds, the instantiated
2563 /// type. Otherwise, produces diagnostics and returns a NULL type.
2564 TypeSourceInfo *Sema::SubstType(TypeSourceInfo *T,
2565                                 const MultiLevelTemplateArgumentList &Args,
2566                                 SourceLocation Loc,
2567                                 DeclarationName Entity,
2568                                 bool AllowDeducedTST) {
2569   assert(!CodeSynthesisContexts.empty() &&
2570          "Cannot perform an instantiation without some context on the "
2571          "instantiation stack");
2572
2573   if (!T->getType()->isInstantiationDependentType() &&
2574       !T->getType()->isVariablyModifiedType())
2575     return T;
2576
2577   TemplateInstantiator Instantiator(*this, Args, Loc, Entity);
2578   return AllowDeducedTST ? Instantiator.TransformTypeWithDeducedTST(T)
2579                          : Instantiator.TransformType(T);
2580 }
2581
2582 TypeSourceInfo *Sema::SubstType(TypeLoc TL,
2583                                 const MultiLevelTemplateArgumentList &Args,
2584                                 SourceLocation Loc,
2585                                 DeclarationName Entity) {
2586   assert(!CodeSynthesisContexts.empty() &&
2587          "Cannot perform an instantiation without some context on the "
2588          "instantiation stack");
2589
2590   if (TL.getType().isNull())
2591     return nullptr;
2592
2593   if (!TL.getType()->isInstantiationDependentType() &&
2594       !TL.getType()->isVariablyModifiedType()) {
2595     // FIXME: Make a copy of the TypeLoc data here, so that we can
2596     // return a new TypeSourceInfo. Inefficient!
2597     TypeLocBuilder TLB;
2598     TLB.pushFullCopy(TL);
2599     return TLB.getTypeSourceInfo(Context, TL.getType());
2600   }
2601
2602   TemplateInstantiator Instantiator(*this, Args, Loc, Entity);
2603   TypeLocBuilder TLB;
2604   TLB.reserve(TL.getFullDataSize());
2605   QualType Result = Instantiator.TransformType(TLB, TL);
2606   if (Result.isNull())
2607     return nullptr;
2608
2609   return TLB.getTypeSourceInfo(Context, Result);
2610 }
2611
2612 /// Deprecated form of the above.
2613 QualType Sema::SubstType(QualType T,
2614                          const MultiLevelTemplateArgumentList &TemplateArgs,
2615                          SourceLocation Loc, DeclarationName Entity) {
2616   assert(!CodeSynthesisContexts.empty() &&
2617          "Cannot perform an instantiation without some context on the "
2618          "instantiation stack");
2619
2620   // If T is not a dependent type or a variably-modified type, there
2621   // is nothing to do.
2622   if (!T->isInstantiationDependentType() && !T->isVariablyModifiedType())
2623     return T;
2624
2625   TemplateInstantiator Instantiator(*this, TemplateArgs, Loc, Entity);
2626   return Instantiator.TransformType(T);
2627 }
2628
2629 static bool NeedsInstantiationAsFunctionType(TypeSourceInfo *T) {
2630   if (T->getType()->isInstantiationDependentType() ||
2631       T->getType()->isVariablyModifiedType())
2632     return true;
2633
2634   TypeLoc TL = T->getTypeLoc().IgnoreParens();
2635   if (!TL.getAs<FunctionProtoTypeLoc>())
2636     return false;
2637
2638   FunctionProtoTypeLoc FP = TL.castAs<FunctionProtoTypeLoc>();
2639   for (ParmVarDecl *P : FP.getParams()) {
2640     // This must be synthesized from a typedef.
2641     if (!P) continue;
2642
2643     // If there are any parameters, a new TypeSourceInfo that refers to the
2644     // instantiated parameters must be built.
2645     return true;
2646   }
2647
2648   return false;
2649 }
2650
2651 /// A form of SubstType intended specifically for instantiating the
2652 /// type of a FunctionDecl.  Its purpose is solely to force the
2653 /// instantiation of default-argument expressions and to avoid
2654 /// instantiating an exception-specification.
2655 TypeSourceInfo *Sema::SubstFunctionDeclType(TypeSourceInfo *T,
2656                                 const MultiLevelTemplateArgumentList &Args,
2657                                 SourceLocation Loc,
2658                                 DeclarationName Entity,
2659                                 CXXRecordDecl *ThisContext,
2660                                 Qualifiers ThisTypeQuals,
2661                                 bool EvaluateConstraints) {
2662   assert(!CodeSynthesisContexts.empty() &&
2663          "Cannot perform an instantiation without some context on the "
2664          "instantiation stack");
2665
2666   if (!NeedsInstantiationAsFunctionType(T))
2667     return T;
2668
2669   TemplateInstantiator Instantiator(*this, Args, Loc, Entity);
2670   Instantiator.setEvaluateConstraints(EvaluateConstraints);
2671
2672   TypeLocBuilder TLB;
2673
2674   TypeLoc TL = T->getTypeLoc();
2675   TLB.reserve(TL.getFullDataSize());
2676
2677   QualType Result;
2678
2679   if (FunctionProtoTypeLoc Proto =
2680           TL.IgnoreParens().getAs<FunctionProtoTypeLoc>()) {
2681     // Instantiate the type, other than its exception specification. The
2682     // exception specification is instantiated in InitFunctionInstantiation
2683     // once we've built the FunctionDecl.
2684     // FIXME: Set the exception specification to EST_Uninstantiated here,
2685     // instead of rebuilding the function type again later.
2686     Result = Instantiator.TransformFunctionProtoType(
2687         TLB, Proto, ThisContext, ThisTypeQuals,
2688         [](FunctionProtoType::ExceptionSpecInfo &ESI,
2689            bool &Changed) { return false; });
2690   } else {
2691     Result = Instantiator.TransformType(TLB, TL);
2692   }
2693   // When there are errors resolving types, clang may use IntTy as a fallback,
2694   // breaking our assumption that function declarations have function types.
2695   if (Result.isNull() || !Result->isFunctionType())
2696     return nullptr;
2697
2698   return TLB.getTypeSourceInfo(Context, Result);
2699 }
2700
2701 bool Sema::SubstExceptionSpec(SourceLocation Loc,
2702                               FunctionProtoType::ExceptionSpecInfo &ESI,
2703                               SmallVectorImpl<QualType> &ExceptionStorage,
2704                               const MultiLevelTemplateArgumentList &Args) {
2705   bool Changed = false;
2706   TemplateInstantiator Instantiator(*this, Args, Loc, DeclarationName());
2707   return Instantiator.TransformExceptionSpec(Loc, ESI, ExceptionStorage,
2708                                              Changed);
2709 }
2710
2711 void Sema::SubstExceptionSpec(FunctionDecl *New, const FunctionProtoType *Proto,
2712                               const MultiLevelTemplateArgumentList &Args) {
2713   FunctionProtoType::ExceptionSpecInfo ESI =
2714       Proto->getExtProtoInfo().ExceptionSpec;
2715
2716   SmallVector<QualType, 4> ExceptionStorage;
2717   if (SubstExceptionSpec(New->getTypeSourceInfo()->getTypeLoc().getEndLoc(),
2718                          ESI, ExceptionStorage, Args))
2719     // On error, recover by dropping the exception specification.
2720     ESI.Type = EST_None;
2721
2722   UpdateExceptionSpec(New, ESI);
2723 }
2724
2725 namespace {
2726
2727   struct GetContainedInventedTypeParmVisitor :
2728     public TypeVisitor<GetContainedInventedTypeParmVisitor,
2729                        TemplateTypeParmDecl *> {
2730     using TypeVisitor<GetContainedInventedTypeParmVisitor,
2731                       TemplateTypeParmDecl *>::Visit;
2732
2733     TemplateTypeParmDecl *Visit(QualType T) {
2734       if (T.isNull())
2735         return nullptr;
2736       return Visit(T.getTypePtr());
2737     }
2738     // The deduced type itself.
2739     TemplateTypeParmDecl *VisitTemplateTypeParmType(
2740         const TemplateTypeParmType *T) {
2741       if (!T->getDecl() || !T->getDecl()->isImplicit())
2742         return nullptr;
2743       return T->getDecl();
2744     }
2745
2746     // Only these types can contain 'auto' types, and subsequently be replaced
2747     // by references to invented parameters.
2748
2749     TemplateTypeParmDecl *VisitElaboratedType(const ElaboratedType *T) {
2750       return Visit(T->getNamedType());
2751     }
2752
2753     TemplateTypeParmDecl *VisitPointerType(const PointerType *T) {
2754       return Visit(T->getPointeeType());
2755     }
2756
2757     TemplateTypeParmDecl *VisitBlockPointerType(const BlockPointerType *T) {
2758       return Visit(T->getPointeeType());
2759     }
2760
2761     TemplateTypeParmDecl *VisitReferenceType(const ReferenceType *T) {
2762       return Visit(T->getPointeeTypeAsWritten());
2763     }
2764
2765     TemplateTypeParmDecl *VisitMemberPointerType(const MemberPointerType *T) {
2766       return Visit(T->getPointeeType());
2767     }
2768
2769     TemplateTypeParmDecl *VisitArrayType(const ArrayType *T) {
2770       return Visit(T->getElementType());
2771     }
2772
2773     TemplateTypeParmDecl *VisitDependentSizedExtVectorType(
2774       const DependentSizedExtVectorType *T) {
2775       return Visit(T->getElementType());
2776     }
2777
2778     TemplateTypeParmDecl *VisitVectorType(const VectorType *T) {
2779       return Visit(T->getElementType());
2780     }
2781
2782     TemplateTypeParmDecl *VisitFunctionProtoType(const FunctionProtoType *T) {
2783       return VisitFunctionType(T);
2784     }
2785
2786     TemplateTypeParmDecl *VisitFunctionType(const FunctionType *T) {
2787       return Visit(T->getReturnType());
2788     }
2789
2790     TemplateTypeParmDecl *VisitParenType(const ParenType *T) {
2791       return Visit(T->getInnerType());
2792     }
2793
2794     TemplateTypeParmDecl *VisitAttributedType(const AttributedType *T) {
2795       return Visit(T->getModifiedType());
2796     }
2797
2798     TemplateTypeParmDecl *VisitMacroQualifiedType(const MacroQualifiedType *T) {
2799       return Visit(T->getUnderlyingType());
2800     }
2801
2802     TemplateTypeParmDecl *VisitAdjustedType(const AdjustedType *T) {
2803       return Visit(T->getOriginalType());
2804     }
2805
2806     TemplateTypeParmDecl *VisitPackExpansionType(const PackExpansionType *T) {
2807       return Visit(T->getPattern());
2808     }
2809   };
2810
2811 } // namespace
2812
2813 bool Sema::SubstTypeConstraint(
2814     TemplateTypeParmDecl *Inst, const TypeConstraint *TC,
2815     const MultiLevelTemplateArgumentList &TemplateArgs,
2816     bool EvaluateConstraints) {
2817   const ASTTemplateArgumentListInfo *TemplArgInfo =
2818       TC->getTemplateArgsAsWritten();
2819
2820   if (!EvaluateConstraints) {
2821       Inst->setTypeConstraint(TC->getConceptReference(),
2822                               TC->getImmediatelyDeclaredConstraint());
2823       return false;
2824   }
2825
2826   TemplateArgumentListInfo InstArgs;
2827
2828   if (TemplArgInfo) {
2829     InstArgs.setLAngleLoc(TemplArgInfo->LAngleLoc);
2830     InstArgs.setRAngleLoc(TemplArgInfo->RAngleLoc);
2831     if (SubstTemplateArguments(TemplArgInfo->arguments(), TemplateArgs,
2832                                InstArgs))
2833       return true;
2834   }
2835   return AttachTypeConstraint(
2836       TC->getNestedNameSpecifierLoc(), TC->getConceptNameInfo(),
2837       TC->getNamedConcept(), &InstArgs, Inst,
2838       Inst->isParameterPack()
2839           ? cast<CXXFoldExpr>(TC->getImmediatelyDeclaredConstraint())
2840                 ->getEllipsisLoc()
2841           : SourceLocation());
2842 }
2843
2844 ParmVarDecl *Sema::SubstParmVarDecl(
2845     ParmVarDecl *OldParm, const MultiLevelTemplateArgumentList &TemplateArgs,
2846     int indexAdjustment, std::optional<unsigned> NumExpansions,
2847     bool ExpectParameterPack, bool EvaluateConstraint) {
2848   TypeSourceInfo *OldDI = OldParm->getTypeSourceInfo();
2849   TypeSourceInfo *NewDI = nullptr;
2850
2851   TypeLoc OldTL = OldDI->getTypeLoc();
2852   if (PackExpansionTypeLoc ExpansionTL = OldTL.getAs<PackExpansionTypeLoc>()) {
2853
2854     // We have a function parameter pack. Substitute into the pattern of the
2855     // expansion.
2856     NewDI = SubstType(ExpansionTL.getPatternLoc(), TemplateArgs,
2857                       OldParm->getLocation(), OldParm->getDeclName());
2858     if (!NewDI)
2859       return nullptr;
2860
2861     if (NewDI->getType()->containsUnexpandedParameterPack()) {
2862       // We still have unexpanded parameter packs, which means that
2863       // our function parameter is still a function parameter pack.
2864       // Therefore, make its type a pack expansion type.
2865       NewDI = CheckPackExpansion(NewDI, ExpansionTL.getEllipsisLoc(),
2866                                  NumExpansions);
2867     } else if (ExpectParameterPack) {
2868       // We expected to get a parameter pack but didn't (because the type
2869       // itself is not a pack expansion type), so complain. This can occur when
2870       // the substitution goes through an alias template that "loses" the
2871       // pack expansion.
2872       Diag(OldParm->getLocation(),
2873            diag::err_function_parameter_pack_without_parameter_packs)
2874         << NewDI->getType();
2875       return nullptr;
2876     }
2877   } else {
2878     NewDI = SubstType(OldDI, TemplateArgs, OldParm->getLocation(),
2879                       OldParm->getDeclName());
2880   }
2881
2882   if (!NewDI)
2883     return nullptr;
2884
2885   if (NewDI->getType()->isVoidType()) {
2886     Diag(OldParm->getLocation(), diag::err_param_with_void_type);
2887     return nullptr;
2888   }
2889
2890   // In abbreviated templates, TemplateTypeParmDecls with possible
2891   // TypeConstraints are created when the parameter list is originally parsed.
2892   // The TypeConstraints can therefore reference other functions parameters in
2893   // the abbreviated function template, which is why we must instantiate them
2894   // here, when the instantiated versions of those referenced parameters are in
2895   // scope.
2896   if (TemplateTypeParmDecl *TTP =
2897           GetContainedInventedTypeParmVisitor().Visit(OldDI->getType())) {
2898     if (const TypeConstraint *TC = TTP->getTypeConstraint()) {
2899       auto *Inst = cast_or_null<TemplateTypeParmDecl>(
2900           FindInstantiatedDecl(TTP->getLocation(), TTP, TemplateArgs));
2901       // We will first get here when instantiating the abbreviated function
2902       // template's described function, but we might also get here later.
2903       // Make sure we do not instantiate the TypeConstraint more than once.
2904       if (Inst && !Inst->getTypeConstraint()) {
2905         if (SubstTypeConstraint(Inst, TC, TemplateArgs, EvaluateConstraint))
2906           return nullptr;
2907       }
2908     }
2909   }
2910
2911   ParmVarDecl *NewParm = CheckParameter(Context.getTranslationUnitDecl(),
2912                                         OldParm->getInnerLocStart(),
2913                                         OldParm->getLocation(),
2914                                         OldParm->getIdentifier(),
2915                                         NewDI->getType(), NewDI,
2916                                         OldParm->getStorageClass());
2917   if (!NewParm)
2918     return nullptr;
2919
2920   // Mark the (new) default argument as uninstantiated (if any).
2921   if (OldParm->hasUninstantiatedDefaultArg()) {
2922     Expr *Arg = OldParm->getUninstantiatedDefaultArg();
2923     NewParm->setUninstantiatedDefaultArg(Arg);
2924   } else if (OldParm->hasUnparsedDefaultArg()) {
2925     NewParm->setUnparsedDefaultArg();
2926     UnparsedDefaultArgInstantiations[OldParm].push_back(NewParm);
2927   } else if (Expr *Arg = OldParm->getDefaultArg()) {
2928     // Default arguments cannot be substituted until the declaration context
2929     // for the associated function or lambda capture class is available.
2930     // This is necessary for cases like the following where construction of
2931     // the lambda capture class for the outer lambda is dependent on the
2932     // parameter types but where the default argument is dependent on the
2933     // outer lambda's declaration context.
2934     //   template <typename T>
2935     //   auto f() {
2936     //     return [](T = []{ return T{}; }()) { return 0; };
2937     //   }
2938     NewParm->setUninstantiatedDefaultArg(Arg);
2939   }
2940
2941   NewParm->setExplicitObjectParameterLoc(
2942       OldParm->getExplicitObjectParamThisLoc());
2943   NewParm->setHasInheritedDefaultArg(OldParm->hasInheritedDefaultArg());
2944
2945   if (OldParm->isParameterPack() && !NewParm->isParameterPack()) {
2946     // Add the new parameter to the instantiated parameter pack.
2947     CurrentInstantiationScope->InstantiatedLocalPackArg(OldParm, NewParm);
2948   } else {
2949     // Introduce an Old -> New mapping
2950     CurrentInstantiationScope->InstantiatedLocal(OldParm, NewParm);
2951   }
2952
2953   // FIXME: OldParm may come from a FunctionProtoType, in which case CurContext
2954   // can be anything, is this right ?
2955   NewParm->setDeclContext(CurContext);
2956
2957   NewParm->setScopeInfo(OldParm->getFunctionScopeDepth(),
2958                         OldParm->getFunctionScopeIndex() + indexAdjustment);
2959
2960   InstantiateAttrs(TemplateArgs, OldParm, NewParm);
2961
2962   return NewParm;
2963 }
2964
2965 /// Substitute the given template arguments into the given set of
2966 /// parameters, producing the set of parameter types that would be generated
2967 /// from such a substitution.
2968 bool Sema::SubstParmTypes(
2969     SourceLocation Loc, ArrayRef<ParmVarDecl *> Params,
2970     const FunctionProtoType::ExtParameterInfo *ExtParamInfos,
2971     const MultiLevelTemplateArgumentList &TemplateArgs,
2972     SmallVectorImpl<QualType> &ParamTypes,
2973     SmallVectorImpl<ParmVarDecl *> *OutParams,
2974     ExtParameterInfoBuilder &ParamInfos) {
2975   assert(!CodeSynthesisContexts.empty() &&
2976          "Cannot perform an instantiation without some context on the "
2977          "instantiation stack");
2978
2979   TemplateInstantiator Instantiator(*this, TemplateArgs, Loc,
2980                                     DeclarationName());
2981   return Instantiator.TransformFunctionTypeParams(
2982       Loc, Params, nullptr, ExtParamInfos, ParamTypes, OutParams, ParamInfos);
2983 }
2984
2985 /// Substitute the given template arguments into the default argument.
2986 bool Sema::SubstDefaultArgument(
2987     SourceLocation Loc,
2988     ParmVarDecl *Param,
2989     const MultiLevelTemplateArgumentList &TemplateArgs,
2990     bool ForCallExpr) {
2991   FunctionDecl *FD = cast<FunctionDecl>(Param->getDeclContext());
2992   Expr *PatternExpr = Param->getUninstantiatedDefaultArg();
2993
2994   EnterExpressionEvaluationContext EvalContext(
2995       *this, ExpressionEvaluationContext::PotentiallyEvaluated, Param);
2996
2997   InstantiatingTemplate Inst(*this, Loc, Param, TemplateArgs.getInnermost());
2998   if (Inst.isInvalid())
2999     return true;
3000   if (Inst.isAlreadyInstantiating()) {
3001     Diag(Param->getBeginLoc(), diag::err_recursive_default_argument) << FD;
3002     Param->setInvalidDecl();
3003     return true;
3004   }
3005
3006   ExprResult Result;
3007   {
3008     // C++ [dcl.fct.default]p5:
3009     //   The names in the [default argument] expression are bound, and
3010     //   the semantic constraints are checked, at the point where the
3011     //   default argument expression appears.
3012     ContextRAII SavedContext(*this, FD);
3013     std::unique_ptr<LocalInstantiationScope> LIS;
3014
3015     if (ForCallExpr) {
3016       // When instantiating a default argument due to use in a call expression,
3017       // an instantiation scope that includes the parameters of the callee is
3018       // required to satisfy references from the default argument. For example:
3019       //   template<typename T> void f(T a, int = decltype(a)());
3020       //   void g() { f(0); }
3021       LIS = std::make_unique<LocalInstantiationScope>(*this);
3022       FunctionDecl *PatternFD = FD->getTemplateInstantiationPattern(
3023           /*ForDefinition*/ false);
3024       if (addInstantiatedParametersToScope(FD, PatternFD, *LIS, TemplateArgs))
3025         return true;
3026     }
3027
3028     runWithSufficientStackSpace(Loc, [&] {
3029       Result = SubstInitializer(PatternExpr, TemplateArgs,
3030                                 /*DirectInit*/false);
3031     });
3032   }
3033   if (Result.isInvalid())
3034     return true;
3035
3036   if (ForCallExpr) {
3037     // Check the expression as an initializer for the parameter.
3038     InitializedEntity Entity
3039       = InitializedEntity::InitializeParameter(Context, Param);
3040     InitializationKind Kind = InitializationKind::CreateCopy(
3041         Param->getLocation(),
3042         /*FIXME:EqualLoc*/ PatternExpr->getBeginLoc());
3043     Expr *ResultE = Result.getAs<Expr>();
3044
3045     InitializationSequence InitSeq(*this, Entity, Kind, ResultE);
3046     Result = InitSeq.Perform(*this, Entity, Kind, ResultE);
3047     if (Result.isInvalid())
3048       return true;
3049
3050     Result =
3051         ActOnFinishFullExpr(Result.getAs<Expr>(), Param->getOuterLocStart(),
3052                             /*DiscardedValue*/ false);
3053   } else {
3054     // FIXME: Obtain the source location for the '=' token.
3055     SourceLocation EqualLoc = PatternExpr->getBeginLoc();
3056     Result = ConvertParamDefaultArgument(Param, Result.getAs<Expr>(), EqualLoc);
3057   }
3058   if (Result.isInvalid())
3059       return true;
3060
3061   // Remember the instantiated default argument.
3062   Param->setDefaultArg(Result.getAs<Expr>());
3063
3064   return false;
3065 }
3066
3067 /// Perform substitution on the base class specifiers of the
3068 /// given class template specialization.
3069 ///
3070 /// Produces a diagnostic and returns true on error, returns false and
3071 /// attaches the instantiated base classes to the class template
3072 /// specialization if successful.
3073 bool
3074 Sema::SubstBaseSpecifiers(CXXRecordDecl *Instantiation,
3075                           CXXRecordDecl *Pattern,
3076                           const MultiLevelTemplateArgumentList &TemplateArgs) {
3077   bool Invalid = false;
3078   SmallVector<CXXBaseSpecifier*, 4> InstantiatedBases;
3079   for (const auto &Base : Pattern->bases()) {
3080     if (!Base.getType()->isDependentType()) {
3081       if (const CXXRecordDecl *RD = Base.getType()->getAsCXXRecordDecl()) {
3082         if (RD->isInvalidDecl())
3083           Instantiation->setInvalidDecl();
3084       }
3085       InstantiatedBases.push_back(new (Context) CXXBaseSpecifier(Base));
3086       continue;
3087     }
3088
3089     SourceLocation EllipsisLoc;
3090     TypeSourceInfo *BaseTypeLoc;
3091     if (Base.isPackExpansion()) {
3092       // This is a pack expansion. See whether we should expand it now, or
3093       // wait until later.
3094       SmallVector<UnexpandedParameterPack, 2> Unexpanded;
3095       collectUnexpandedParameterPacks(Base.getTypeSourceInfo()->getTypeLoc(),
3096                                       Unexpanded);
3097       bool ShouldExpand = false;
3098       bool RetainExpansion = false;
3099       std::optional<unsigned> NumExpansions;
3100       if (CheckParameterPacksForExpansion(Base.getEllipsisLoc(),
3101                                           Base.getSourceRange(),
3102                                           Unexpanded,
3103                                           TemplateArgs, ShouldExpand,
3104                                           RetainExpansion,
3105                                           NumExpansions)) {
3106         Invalid = true;
3107         continue;
3108       }
3109
3110       // If we should expand this pack expansion now, do so.
3111       if (ShouldExpand) {
3112         for (unsigned I = 0; I != *NumExpansions; ++I) {
3113             Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(*this, I);
3114
3115           TypeSourceInfo *BaseTypeLoc = SubstType(Base.getTypeSourceInfo(),
3116                                                   TemplateArgs,
3117                                               Base.getSourceRange().getBegin(),
3118                                                   DeclarationName());
3119           if (!BaseTypeLoc) {
3120             Invalid = true;
3121             continue;
3122           }
3123
3124           if (CXXBaseSpecifier *InstantiatedBase
3125                 = CheckBaseSpecifier(Instantiation,
3126                                      Base.getSourceRange(),
3127                                      Base.isVirtual(),
3128                                      Base.getAccessSpecifierAsWritten(),
3129                                      BaseTypeLoc,
3130                                      SourceLocation()))
3131             InstantiatedBases.push_back(InstantiatedBase);
3132           else
3133             Invalid = true;
3134         }
3135
3136         continue;
3137       }
3138
3139       // The resulting base specifier will (still) be a pack expansion.
3140       EllipsisLoc = Base.getEllipsisLoc();
3141       Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(*this, -1);
3142       BaseTypeLoc = SubstType(Base.getTypeSourceInfo(),
3143                               TemplateArgs,
3144                               Base.getSourceRange().getBegin(),
3145                               DeclarationName());
3146     } else {
3147       BaseTypeLoc = SubstType(Base.getTypeSourceInfo(),
3148                               TemplateArgs,
3149                               Base.getSourceRange().getBegin(),
3150                               DeclarationName());
3151     }
3152
3153     if (!BaseTypeLoc) {
3154       Invalid = true;
3155       continue;
3156     }
3157
3158     if (CXXBaseSpecifier *InstantiatedBase
3159           = CheckBaseSpecifier(Instantiation,
3160                                Base.getSourceRange(),
3161                                Base.isVirtual(),
3162                                Base.getAccessSpecifierAsWritten(),
3163                                BaseTypeLoc,
3164                                EllipsisLoc))
3165       InstantiatedBases.push_back(InstantiatedBase);
3166     else
3167       Invalid = true;
3168   }
3169
3170   if (!Invalid && AttachBaseSpecifiers(Instantiation, InstantiatedBases))
3171     Invalid = true;
3172
3173   return Invalid;
3174 }
3175
3176 // Defined via #include from SemaTemplateInstantiateDecl.cpp
3177 namespace clang {
3178   namespace sema {
3179     Attr *instantiateTemplateAttribute(const Attr *At, ASTContext &C, Sema &S,
3180                             const MultiLevelTemplateArgumentList &TemplateArgs);
3181     Attr *instantiateTemplateAttributeForDecl(
3182         const Attr *At, ASTContext &C, Sema &S,
3183         const MultiLevelTemplateArgumentList &TemplateArgs);
3184   }
3185 }
3186
3187 /// Instantiate the definition of a class from a given pattern.
3188 ///
3189 /// \param PointOfInstantiation The point of instantiation within the
3190 /// source code.
3191 ///
3192 /// \param Instantiation is the declaration whose definition is being
3193 /// instantiated. This will be either a class template specialization
3194 /// or a member class of a class template specialization.
3195 ///
3196 /// \param Pattern is the pattern from which the instantiation
3197 /// occurs. This will be either the declaration of a class template or
3198 /// the declaration of a member class of a class template.
3199 ///
3200 /// \param TemplateArgs The template arguments to be substituted into
3201 /// the pattern.
3202 ///
3203 /// \param TSK the kind of implicit or explicit instantiation to perform.
3204 ///
3205 /// \param Complain whether to complain if the class cannot be instantiated due
3206 /// to the lack of a definition.
3207 ///
3208 /// \returns true if an error occurred, false otherwise.
3209 bool
3210 Sema::InstantiateClass(SourceLocation PointOfInstantiation,
3211                        CXXRecordDecl *Instantiation, CXXRecordDecl *Pattern,
3212                        const MultiLevelTemplateArgumentList &TemplateArgs,
3213                        TemplateSpecializationKind TSK,
3214                        bool Complain) {
3215   CXXRecordDecl *PatternDef
3216     = cast_or_null<CXXRecordDecl>(Pattern->getDefinition());
3217   if (DiagnoseUninstantiableTemplate(PointOfInstantiation, Instantiation,
3218                                 Instantiation->getInstantiatedFromMemberClass(),
3219                                      Pattern, PatternDef, TSK, Complain))
3220     return true;
3221
3222   llvm::TimeTraceScope TimeScope("InstantiateClass", [&]() {
3223     std::string Name;
3224     llvm::raw_string_ostream OS(Name);
3225     Instantiation->getNameForDiagnostic(OS, getPrintingPolicy(),
3226                                         /*Qualified=*/true);
3227     return Name;
3228   });
3229
3230   Pattern = PatternDef;
3231
3232   // Record the point of instantiation.
3233   if (MemberSpecializationInfo *MSInfo
3234         = Instantiation->getMemberSpecializationInfo()) {
3235     MSInfo->setTemplateSpecializationKind(TSK);
3236     MSInfo->setPointOfInstantiation(PointOfInstantiation);
3237   } else if (ClassTemplateSpecializationDecl *Spec
3238         = dyn_cast<ClassTemplateSpecializationDecl>(Instantiation)) {
3239     Spec->setTemplateSpecializationKind(TSK);
3240     Spec->setPointOfInstantiation(PointOfInstantiation);
3241   }
3242
3243   InstantiatingTemplate Inst(*this, PointOfInstantiation, Instantiation);
3244   if (Inst.isInvalid())
3245     return true;
3246   assert(!Inst.isAlreadyInstantiating() && "should have been caught by caller");
3247   PrettyDeclStackTraceEntry CrashInfo(Context, Instantiation, SourceLocation(),
3248                                       "instantiating class definition");
3249
3250   // Enter the scope of this instantiation. We don't use
3251   // PushDeclContext because we don't have a scope.
3252   ContextRAII SavedContext(*this, Instantiation);
3253   EnterExpressionEvaluationContext EvalContext(
3254       *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
3255
3256   // If this is an instantiation of a local class, merge this local
3257   // instantiation scope with the enclosing scope. Otherwise, every
3258   // instantiation of a class has its own local instantiation scope.
3259   bool MergeWithParentScope = !Instantiation->isDefinedOutsideFunctionOrMethod();
3260   LocalInstantiationScope Scope(*this, MergeWithParentScope);
3261
3262   // Some class state isn't processed immediately but delayed till class
3263   // instantiation completes. We may not be ready to handle any delayed state
3264   // already on the stack as it might correspond to a different class, so save
3265   // it now and put it back later.
3266   SavePendingParsedClassStateRAII SavedPendingParsedClassState(*this);
3267
3268   // Pull attributes from the pattern onto the instantiation.
3269   InstantiateAttrs(TemplateArgs, Pattern, Instantiation);
3270
3271   // Start the definition of this instantiation.
3272   Instantiation->startDefinition();
3273
3274   // The instantiation is visible here, even if it was first declared in an
3275   // unimported module.
3276   Instantiation->setVisibleDespiteOwningModule();
3277
3278   // FIXME: This loses the as-written tag kind for an explicit instantiation.
3279   Instantiation->setTagKind(Pattern->getTagKind());
3280
3281   // Do substitution on the base class specifiers.
3282   if (SubstBaseSpecifiers(Instantiation, Pattern, TemplateArgs))
3283     Instantiation->setInvalidDecl();
3284
3285   TemplateDeclInstantiator Instantiator(*this, Instantiation, TemplateArgs);
3286   Instantiator.setEvaluateConstraints(false);
3287   SmallVector<Decl*, 4> Fields;
3288   // Delay instantiation of late parsed attributes.
3289   LateInstantiatedAttrVec LateAttrs;
3290   Instantiator.enableLateAttributeInstantiation(&LateAttrs);
3291
3292   bool MightHaveConstexprVirtualFunctions = false;
3293   for (auto *Member : Pattern->decls()) {
3294     // Don't instantiate members not belonging in this semantic context.
3295     // e.g. for:
3296     // @code
3297     //    template <int i> class A {
3298     //      class B *g;
3299     //    };
3300     // @endcode
3301     // 'class B' has the template as lexical context but semantically it is
3302     // introduced in namespace scope.
3303     if (Member->getDeclContext() != Pattern)
3304       continue;
3305
3306     // BlockDecls can appear in a default-member-initializer. They must be the
3307     // child of a BlockExpr, so we only know how to instantiate them from there.
3308     // Similarly, lambda closure types are recreated when instantiating the
3309     // corresponding LambdaExpr.
3310     if (isa<BlockDecl>(Member) ||
3311         (isa<CXXRecordDecl>(Member) && cast<CXXRecordDecl>(Member)->isLambda()))
3312       continue;
3313
3314     if (Member->isInvalidDecl()) {
3315       Instantiation->setInvalidDecl();
3316       continue;
3317     }
3318
3319     Decl *NewMember = Instantiator.Visit(Member);
3320     if (NewMember) {
3321       if (FieldDecl *Field = dyn_cast<FieldDecl>(NewMember)) {
3322         Fields.push_back(Field);
3323       } else if (EnumDecl *Enum = dyn_cast<EnumDecl>(NewMember)) {
3324         // C++11 [temp.inst]p1: The implicit instantiation of a class template
3325         // specialization causes the implicit instantiation of the definitions
3326         // of unscoped member enumerations.
3327         // Record a point of instantiation for this implicit instantiation.
3328         if (TSK == TSK_ImplicitInstantiation && !Enum->isScoped() &&
3329             Enum->isCompleteDefinition()) {
3330           MemberSpecializationInfo *MSInfo =Enum->getMemberSpecializationInfo();
3331           assert(MSInfo && "no spec info for member enum specialization");
3332           MSInfo->setTemplateSpecializationKind(TSK_ImplicitInstantiation);
3333           MSInfo->setPointOfInstantiation(PointOfInstantiation);
3334         }
3335       } else if (StaticAssertDecl *SA = dyn_cast<StaticAssertDecl>(NewMember)) {
3336         if (SA->isFailed()) {
3337           // A static_assert failed. Bail out; instantiating this
3338           // class is probably not meaningful.
3339           Instantiation->setInvalidDecl();
3340           break;
3341         }
3342       } else if (CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(NewMember)) {
3343         if (MD->isConstexpr() && !MD->getFriendObjectKind() &&
3344             (MD->isVirtualAsWritten() || Instantiation->getNumBases()))
3345           MightHaveConstexprVirtualFunctions = true;
3346       }
3347
3348       if (NewMember->isInvalidDecl())
3349         Instantiation->setInvalidDecl();
3350     } else {
3351       // FIXME: Eventually, a NULL return will mean that one of the
3352       // instantiations was a semantic disaster, and we'll want to mark the
3353       // declaration invalid.
3354       // For now, we expect to skip some members that we can't yet handle.
3355     }
3356   }
3357
3358   // Finish checking fields.
3359   ActOnFields(nullptr, Instantiation->getLocation(), Instantiation, Fields,
3360               SourceLocation(), SourceLocation(), ParsedAttributesView());
3361   CheckCompletedCXXClass(nullptr, Instantiation);
3362
3363   // Default arguments are parsed, if not instantiated. We can go instantiate
3364   // default arg exprs for default constructors if necessary now. Unless we're
3365   // parsing a class, in which case wait until that's finished.
3366   if (ParsingClassDepth == 0)
3367     ActOnFinishCXXNonNestedClass();
3368
3369   // Instantiate late parsed attributes, and attach them to their decls.
3370   // See Sema::InstantiateAttrs
3371   for (LateInstantiatedAttrVec::iterator I = LateAttrs.begin(),
3372        E = LateAttrs.end(); I != E; ++I) {
3373     assert(CurrentInstantiationScope == Instantiator.getStartingScope());
3374     CurrentInstantiationScope = I->Scope;
3375
3376     // Allow 'this' within late-parsed attributes.
3377     auto *ND = cast<NamedDecl>(I->NewDecl);
3378     auto *ThisContext = dyn_cast_or_null<CXXRecordDecl>(ND->getDeclContext());
3379     CXXThisScopeRAII ThisScope(*this, ThisContext, Qualifiers(),
3380                                ND->isCXXInstanceMember());
3381
3382     Attr *NewAttr =
3383       instantiateTemplateAttribute(I->TmplAttr, Context, *this, TemplateArgs);
3384     if (NewAttr)
3385       I->NewDecl->addAttr(NewAttr);
3386     LocalInstantiationScope::deleteScopes(I->Scope,
3387                                           Instantiator.getStartingScope());
3388   }
3389   Instantiator.disableLateAttributeInstantiation();
3390   LateAttrs.clear();
3391
3392   ActOnFinishDelayedMemberInitializers(Instantiation);
3393
3394   // FIXME: We should do something similar for explicit instantiations so they
3395   // end up in the right module.
3396   if (TSK == TSK_ImplicitInstantiation) {
3397     Instantiation->setLocation(Pattern->getLocation());
3398     Instantiation->setLocStart(Pattern->getInnerLocStart());
3399     Instantiation->setBraceRange(Pattern->getBraceRange());
3400   }
3401
3402   if (!Instantiation->isInvalidDecl()) {
3403     // Perform any dependent diagnostics from the pattern.
3404     if (Pattern->isDependentContext())
3405       PerformDependentDiagnostics(Pattern, TemplateArgs);
3406
3407     // Instantiate any out-of-line class template partial
3408     // specializations now.
3409     for (TemplateDeclInstantiator::delayed_partial_spec_iterator
3410               P = Instantiator.delayed_partial_spec_begin(),
3411            PEnd = Instantiator.delayed_partial_spec_end();
3412          P != PEnd; ++P) {
3413       if (!Instantiator.InstantiateClassTemplatePartialSpecialization(
3414               P->first, P->second)) {
3415         Instantiation->setInvalidDecl();
3416         break;
3417       }
3418     }
3419
3420     // Instantiate any out-of-line variable template partial
3421     // specializations now.
3422     for (TemplateDeclInstantiator::delayed_var_partial_spec_iterator
3423               P = Instantiator.delayed_var_partial_spec_begin(),
3424            PEnd = Instantiator.delayed_var_partial_spec_end();
3425          P != PEnd; ++P) {
3426       if (!Instantiator.InstantiateVarTemplatePartialSpecialization(
3427               P->first, P->second)) {
3428         Instantiation->setInvalidDecl();
3429         break;
3430       }
3431     }
3432   }
3433
3434   // Exit the scope of this instantiation.
3435   SavedContext.pop();
3436
3437   if (!Instantiation->isInvalidDecl()) {
3438     // Always emit the vtable for an explicit instantiation definition
3439     // of a polymorphic class template specialization. Otherwise, eagerly
3440     // instantiate only constexpr virtual functions in preparation for their use
3441     // in constant evaluation.
3442     if (TSK == TSK_ExplicitInstantiationDefinition)
3443       MarkVTableUsed(PointOfInstantiation, Instantiation, true);
3444     else if (MightHaveConstexprVirtualFunctions)
3445       MarkVirtualMembersReferenced(PointOfInstantiation, Instantiation,
3446                                    /*ConstexprOnly*/ true);
3447   }
3448
3449   Consumer.HandleTagDeclDefinition(Instantiation);
3450
3451   return Instantiation->isInvalidDecl();
3452 }
3453
3454 /// Instantiate the definition of an enum from a given pattern.
3455 ///
3456 /// \param PointOfInstantiation The point of instantiation within the
3457 ///        source code.
3458 /// \param Instantiation is the declaration whose definition is being
3459 ///        instantiated. This will be a member enumeration of a class
3460 ///        temploid specialization, or a local enumeration within a
3461 ///        function temploid specialization.
3462 /// \param Pattern The templated declaration from which the instantiation
3463 ///        occurs.
3464 /// \param TemplateArgs The template arguments to be substituted into
3465 ///        the pattern.
3466 /// \param TSK The kind of implicit or explicit instantiation to perform.
3467 ///
3468 /// \return \c true if an error occurred, \c false otherwise.
3469 bool Sema::InstantiateEnum(SourceLocation PointOfInstantiation,
3470                            EnumDecl *Instantiation, EnumDecl *Pattern,
3471                            const MultiLevelTemplateArgumentList &TemplateArgs,
3472                            TemplateSpecializationKind TSK) {
3473   EnumDecl *PatternDef = Pattern->getDefinition();
3474   if (DiagnoseUninstantiableTemplate(PointOfInstantiation, Instantiation,
3475                                  Instantiation->getInstantiatedFromMemberEnum(),
3476                                      Pattern, PatternDef, TSK,/*Complain*/true))
3477     return true;
3478   Pattern = PatternDef;
3479
3480   // Record the point of instantiation.
3481   if (MemberSpecializationInfo *MSInfo
3482         = Instantiation->getMemberSpecializationInfo()) {
3483     MSInfo->setTemplateSpecializationKind(TSK);
3484     MSInfo->setPointOfInstantiation(PointOfInstantiation);
3485   }
3486
3487   InstantiatingTemplate Inst(*this, PointOfInstantiation, Instantiation);
3488   if (Inst.isInvalid())
3489     return true;
3490   if (Inst.isAlreadyInstantiating())
3491     return false;
3492   PrettyDeclStackTraceEntry CrashInfo(Context, Instantiation, SourceLocation(),
3493                                       "instantiating enum definition");
3494
3495   // The instantiation is visible here, even if it was first declared in an
3496   // unimported module.
3497   Instantiation->setVisibleDespiteOwningModule();
3498
3499   // Enter the scope of this instantiation. We don't use
3500   // PushDeclContext because we don't have a scope.
3501   ContextRAII SavedContext(*this, Instantiation);
3502   EnterExpressionEvaluationContext EvalContext(
3503       *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
3504
3505   LocalInstantiationScope Scope(*this, /*MergeWithParentScope*/true);
3506
3507   // Pull attributes from the pattern onto the instantiation.
3508   InstantiateAttrs(TemplateArgs, Pattern, Instantiation);
3509
3510   TemplateDeclInstantiator Instantiator(*this, Instantiation, TemplateArgs);
3511   Instantiator.InstantiateEnumDefinition(Instantiation, Pattern);
3512
3513   // Exit the scope of this instantiation.
3514   SavedContext.pop();
3515
3516   return Instantiation->isInvalidDecl();
3517 }
3518
3519
3520 /// Instantiate the definition of a field from the given pattern.
3521 ///
3522 /// \param PointOfInstantiation The point of instantiation within the
3523 ///        source code.
3524 /// \param Instantiation is the declaration whose definition is being
3525 ///        instantiated. This will be a class of a class temploid
3526 ///        specialization, or a local enumeration within a function temploid
3527 ///        specialization.
3528 /// \param Pattern The templated declaration from which the instantiation
3529 ///        occurs.
3530 /// \param TemplateArgs The template arguments to be substituted into
3531 ///        the pattern.
3532 ///
3533 /// \return \c true if an error occurred, \c false otherwise.
3534 bool Sema::InstantiateInClassInitializer(
3535     SourceLocation PointOfInstantiation, FieldDecl *Instantiation,
3536     FieldDecl *Pattern, const MultiLevelTemplateArgumentList &TemplateArgs) {
3537   // If there is no initializer, we don't need to do anything.
3538   if (!Pattern->hasInClassInitializer())
3539     return false;
3540
3541   assert(Instantiation->getInClassInitStyle() ==
3542              Pattern->getInClassInitStyle() &&
3543          "pattern and instantiation disagree about init style");
3544
3545   // Error out if we haven't parsed the initializer of the pattern yet because
3546   // we are waiting for the closing brace of the outer class.
3547   Expr *OldInit = Pattern->getInClassInitializer();
3548   if (!OldInit) {
3549     RecordDecl *PatternRD = Pattern->getParent();
3550     RecordDecl *OutermostClass = PatternRD->getOuterLexicalRecordContext();
3551     Diag(PointOfInstantiation,
3552          diag::err_default_member_initializer_not_yet_parsed)
3553         << OutermostClass << Pattern;
3554     Diag(Pattern->getEndLoc(),
3555          diag::note_default_member_initializer_not_yet_parsed);
3556     Instantiation->setInvalidDecl();
3557     return true;
3558   }
3559
3560   InstantiatingTemplate Inst(*this, PointOfInstantiation, Instantiation);
3561   if (Inst.isInvalid())
3562     return true;
3563   if (Inst.isAlreadyInstantiating()) {
3564     // Error out if we hit an instantiation cycle for this initializer.
3565     Diag(PointOfInstantiation, diag::err_default_member_initializer_cycle)
3566       << Instantiation;
3567     return true;
3568   }
3569   PrettyDeclStackTraceEntry CrashInfo(Context, Instantiation, SourceLocation(),
3570                                       "instantiating default member init");
3571
3572   // Enter the scope of this instantiation. We don't use PushDeclContext because
3573   // we don't have a scope.
3574   ContextRAII SavedContext(*this, Instantiation->getParent());
3575   EnterExpressionEvaluationContext EvalContext(
3576       *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
3577   ExprEvalContexts.back().DelayedDefaultInitializationContext = {
3578       PointOfInstantiation, Instantiation, CurContext};
3579
3580   LocalInstantiationScope Scope(*this, true);
3581
3582   // Instantiate the initializer.
3583   ActOnStartCXXInClassMemberInitializer();
3584   CXXThisScopeRAII ThisScope(*this, Instantiation->getParent(), Qualifiers());
3585
3586   ExprResult NewInit = SubstInitializer(OldInit, TemplateArgs,
3587                                         /*CXXDirectInit=*/false);
3588   Expr *Init = NewInit.get();
3589   assert((!Init || !isa<ParenListExpr>(Init)) && "call-style init in class");
3590   ActOnFinishCXXInClassMemberInitializer(
3591       Instantiation, Init ? Init->getBeginLoc() : SourceLocation(), Init);
3592
3593   if (auto *L = getASTMutationListener())
3594     L->DefaultMemberInitializerInstantiated(Instantiation);
3595
3596   // Return true if the in-class initializer is still missing.
3597   return !Instantiation->getInClassInitializer();
3598 }
3599
3600 namespace {
3601   /// A partial specialization whose template arguments have matched
3602   /// a given template-id.
3603   struct PartialSpecMatchResult {
3604     ClassTemplatePartialSpecializationDecl *Partial;
3605     TemplateArgumentList *Args;
3606   };
3607 }
3608
3609 bool Sema::usesPartialOrExplicitSpecialization(
3610     SourceLocation Loc, ClassTemplateSpecializationDecl *ClassTemplateSpec) {
3611   if (ClassTemplateSpec->getTemplateSpecializationKind() ==
3612       TSK_ExplicitSpecialization)
3613     return true;
3614
3615   SmallVector<ClassTemplatePartialSpecializationDecl *, 4> PartialSpecs;
3616   ClassTemplateSpec->getSpecializedTemplate()
3617                    ->getPartialSpecializations(PartialSpecs);
3618   for (unsigned I = 0, N = PartialSpecs.size(); I != N; ++I) {
3619     TemplateDeductionInfo Info(Loc);
3620     if (!DeduceTemplateArguments(PartialSpecs[I],
3621                                  ClassTemplateSpec->getTemplateArgs(), Info))
3622       return true;
3623   }
3624
3625   return false;
3626 }
3627
3628 /// Get the instantiation pattern to use to instantiate the definition of a
3629 /// given ClassTemplateSpecializationDecl (either the pattern of the primary
3630 /// template or of a partial specialization).
3631 static ActionResult<CXXRecordDecl *>
3632 getPatternForClassTemplateSpecialization(
3633     Sema &S, SourceLocation PointOfInstantiation,
3634     ClassTemplateSpecializationDecl *ClassTemplateSpec,
3635     TemplateSpecializationKind TSK) {
3636   Sema::InstantiatingTemplate Inst(S, PointOfInstantiation, ClassTemplateSpec);
3637   if (Inst.isInvalid())
3638     return {/*Invalid=*/true};
3639   if (Inst.isAlreadyInstantiating())
3640     return {/*Invalid=*/false};
3641
3642   llvm::PointerUnion<ClassTemplateDecl *,
3643                      ClassTemplatePartialSpecializationDecl *>
3644       Specialized = ClassTemplateSpec->getSpecializedTemplateOrPartial();
3645   if (!Specialized.is<ClassTemplatePartialSpecializationDecl *>()) {
3646     // Find best matching specialization.
3647     ClassTemplateDecl *Template = ClassTemplateSpec->getSpecializedTemplate();
3648
3649     // C++ [temp.class.spec.match]p1:
3650     //   When a class template is used in a context that requires an
3651     //   instantiation of the class, it is necessary to determine
3652     //   whether the instantiation is to be generated using the primary
3653     //   template or one of the partial specializations. This is done by
3654     //   matching the template arguments of the class template
3655     //   specialization with the template argument lists of the partial
3656     //   specializations.
3657     typedef PartialSpecMatchResult MatchResult;
3658     SmallVector<MatchResult, 4> Matched;
3659     SmallVector<ClassTemplatePartialSpecializationDecl *, 4> PartialSpecs;
3660     Template->getPartialSpecializations(PartialSpecs);
3661     TemplateSpecCandidateSet FailedCandidates(PointOfInstantiation);
3662     for (unsigned I = 0, N = PartialSpecs.size(); I != N; ++I) {
3663       ClassTemplatePartialSpecializationDecl *Partial = PartialSpecs[I];
3664       TemplateDeductionInfo Info(FailedCandidates.getLocation());
3665       if (Sema::TemplateDeductionResult Result = S.DeduceTemplateArguments(
3666               Partial, ClassTemplateSpec->getTemplateArgs(), Info)) {
3667         // Store the failed-deduction information for use in diagnostics, later.
3668         // TODO: Actually use the failed-deduction info?
3669         FailedCandidates.addCandidate().set(
3670             DeclAccessPair::make(Template, AS_public), Partial,
3671             MakeDeductionFailureInfo(S.Context, Result, Info));
3672         (void)Result;
3673       } else {
3674         Matched.push_back(PartialSpecMatchResult());
3675         Matched.back().Partial = Partial;
3676         Matched.back().Args = Info.takeCanonical();
3677       }
3678     }
3679
3680     // If we're dealing with a member template where the template parameters
3681     // have been instantiated, this provides the original template parameters
3682     // from which the member template's parameters were instantiated.
3683
3684     if (Matched.size() >= 1) {
3685       SmallVectorImpl<MatchResult>::iterator Best = Matched.begin();
3686       if (Matched.size() == 1) {
3687         //   -- If exactly one matching specialization is found, the
3688         //      instantiation is generated from that specialization.
3689         // We don't need to do anything for this.
3690       } else {
3691         //   -- If more than one matching specialization is found, the
3692         //      partial order rules (14.5.4.2) are used to determine
3693         //      whether one of the specializations is more specialized
3694         //      than the others. If none of the specializations is more
3695         //      specialized than all of the other matching
3696         //      specializations, then the use of the class template is
3697         //      ambiguous and the program is ill-formed.
3698         for (SmallVectorImpl<MatchResult>::iterator P = Best + 1,
3699                                                  PEnd = Matched.end();
3700              P != PEnd; ++P) {
3701           if (S.getMoreSpecializedPartialSpecialization(
3702                   P->Partial, Best->Partial, PointOfInstantiation) ==
3703               P->Partial)
3704             Best = P;
3705         }
3706
3707         // Determine if the best partial specialization is more specialized than
3708         // the others.
3709         bool Ambiguous = false;
3710         for (SmallVectorImpl<MatchResult>::iterator P = Matched.begin(),
3711                                                  PEnd = Matched.end();
3712              P != PEnd; ++P) {
3713           if (P != Best && S.getMoreSpecializedPartialSpecialization(
3714                                P->Partial, Best->Partial,
3715                                PointOfInstantiation) != Best->Partial) {
3716             Ambiguous = true;
3717             break;
3718           }
3719         }
3720
3721         if (Ambiguous) {
3722           // Partial ordering did not produce a clear winner. Complain.
3723           Inst.Clear();
3724           ClassTemplateSpec->setInvalidDecl();
3725           S.Diag(PointOfInstantiation,
3726                  diag::err_partial_spec_ordering_ambiguous)
3727               << ClassTemplateSpec;
3728
3729           // Print the matching partial specializations.
3730           for (SmallVectorImpl<MatchResult>::iterator P = Matched.begin(),
3731                                                    PEnd = Matched.end();
3732                P != PEnd; ++P)
3733             S.Diag(P->Partial->getLocation(), diag::note_partial_spec_match)
3734                 << S.getTemplateArgumentBindingsText(
3735                        P->Partial->getTemplateParameters(), *P->Args);
3736
3737           return {/*Invalid=*/true};
3738         }
3739       }
3740
3741       ClassTemplateSpec->setInstantiationOf(Best->Partial, Best->Args);
3742     } else {
3743       //   -- If no matches are found, the instantiation is generated
3744       //      from the primary template.
3745     }
3746   }
3747
3748   CXXRecordDecl *Pattern = nullptr;
3749   Specialized = ClassTemplateSpec->getSpecializedTemplateOrPartial();
3750   if (auto *PartialSpec =
3751           Specialized.dyn_cast<ClassTemplatePartialSpecializationDecl *>()) {
3752     // Instantiate using the best class template partial specialization.
3753     while (PartialSpec->getInstantiatedFromMember()) {
3754       // If we've found an explicit specialization of this class template,
3755       // stop here and use that as the pattern.
3756       if (PartialSpec->isMemberSpecialization())
3757         break;
3758
3759       PartialSpec = PartialSpec->getInstantiatedFromMember();
3760     }
3761     Pattern = PartialSpec;
3762   } else {
3763     ClassTemplateDecl *Template = ClassTemplateSpec->getSpecializedTemplate();
3764     while (Template->getInstantiatedFromMemberTemplate()) {
3765       // If we've found an explicit specialization of this class template,
3766       // stop here and use that as the pattern.
3767       if (Template->isMemberSpecialization())
3768         break;
3769
3770       Template = Template->getInstantiatedFromMemberTemplate();
3771     }
3772     Pattern = Template->getTemplatedDecl();
3773   }
3774
3775   return Pattern;
3776 }
3777
3778 bool Sema::InstantiateClassTemplateSpecialization(
3779     SourceLocation PointOfInstantiation,
3780     ClassTemplateSpecializationDecl *ClassTemplateSpec,
3781     TemplateSpecializationKind TSK, bool Complain) {
3782   // Perform the actual instantiation on the canonical declaration.
3783   ClassTemplateSpec = cast<ClassTemplateSpecializationDecl>(
3784       ClassTemplateSpec->getCanonicalDecl());
3785   if (ClassTemplateSpec->isInvalidDecl())
3786     return true;
3787
3788   ActionResult<CXXRecordDecl *> Pattern =
3789       getPatternForClassTemplateSpecialization(*this, PointOfInstantiation,
3790                                                ClassTemplateSpec, TSK);
3791   if (!Pattern.isUsable())
3792     return Pattern.isInvalid();
3793
3794   return InstantiateClass(
3795       PointOfInstantiation, ClassTemplateSpec, Pattern.get(),
3796       getTemplateInstantiationArgs(ClassTemplateSpec), TSK, Complain);
3797 }
3798
3799 /// Instantiates the definitions of all of the member
3800 /// of the given class, which is an instantiation of a class template
3801 /// or a member class of a template.
3802 void
3803 Sema::InstantiateClassMembers(SourceLocation PointOfInstantiation,
3804                               CXXRecordDecl *Instantiation,
3805                         const MultiLevelTemplateArgumentList &TemplateArgs,
3806                               TemplateSpecializationKind TSK) {
3807   // FIXME: We need to notify the ASTMutationListener that we did all of these
3808   // things, in case we have an explicit instantiation definition in a PCM, a
3809   // module, or preamble, and the declaration is in an imported AST.
3810   assert(
3811       (TSK == TSK_ExplicitInstantiationDefinition ||
3812        TSK == TSK_ExplicitInstantiationDeclaration ||
3813        (TSK == TSK_ImplicitInstantiation && Instantiation->isLocalClass())) &&
3814       "Unexpected template specialization kind!");
3815   for (auto *D : Instantiation->decls()) {
3816     bool SuppressNew = false;
3817     if (auto *Function = dyn_cast<FunctionDecl>(D)) {
3818       if (FunctionDecl *Pattern =
3819               Function->getInstantiatedFromMemberFunction()) {
3820
3821         if (Function->isIneligibleOrNotSelected())
3822           continue;
3823
3824         if (Function->getTrailingRequiresClause()) {
3825           ConstraintSatisfaction Satisfaction;
3826           if (CheckFunctionConstraints(Function, Satisfaction) ||
3827               !Satisfaction.IsSatisfied) {
3828             continue;
3829           }
3830         }
3831
3832         if (Function->hasAttr<ExcludeFromExplicitInstantiationAttr>())
3833           continue;
3834
3835         MemberSpecializationInfo *MSInfo =
3836             Function->getMemberSpecializationInfo();
3837         assert(MSInfo && "No member specialization information?");
3838         if (MSInfo->getTemplateSpecializationKind()
3839                                                  == TSK_ExplicitSpecialization)
3840           continue;
3841
3842         if (CheckSpecializationInstantiationRedecl(PointOfInstantiation, TSK,
3843                                                    Function,
3844                                         MSInfo->getTemplateSpecializationKind(),
3845                                               MSInfo->getPointOfInstantiation(),
3846                                                    SuppressNew) ||
3847             SuppressNew)
3848           continue;
3849
3850         // C++11 [temp.explicit]p8:
3851         //   An explicit instantiation definition that names a class template
3852         //   specialization explicitly instantiates the class template
3853         //   specialization and is only an explicit instantiation definition
3854         //   of members whose definition is visible at the point of
3855         //   instantiation.
3856         if (TSK == TSK_ExplicitInstantiationDefinition && !Pattern->isDefined())
3857           continue;
3858
3859         Function->setTemplateSpecializationKind(TSK, PointOfInstantiation);
3860
3861         if (Function->isDefined()) {
3862           // Let the ASTConsumer know that this function has been explicitly
3863           // instantiated now, and its linkage might have changed.
3864           Consumer.HandleTopLevelDecl(DeclGroupRef(Function));
3865         } else if (TSK == TSK_ExplicitInstantiationDefinition) {
3866           InstantiateFunctionDefinition(PointOfInstantiation, Function);
3867         } else if (TSK == TSK_ImplicitInstantiation) {
3868           PendingLocalImplicitInstantiations.push_back(
3869               std::make_pair(Function, PointOfInstantiation));
3870         }
3871       }
3872     } else if (auto *Var = dyn_cast<VarDecl>(D)) {
3873       if (isa<VarTemplateSpecializationDecl>(Var))
3874         continue;
3875
3876       if (Var->isStaticDataMember()) {
3877         if (Var->hasAttr<ExcludeFromExplicitInstantiationAttr>())
3878           continue;
3879
3880         MemberSpecializationInfo *MSInfo = Var->getMemberSpecializationInfo();
3881         assert(MSInfo && "No member specialization information?");
3882         if (MSInfo->getTemplateSpecializationKind()
3883                                                  == TSK_ExplicitSpecialization)
3884           continue;
3885
3886         if (CheckSpecializationInstantiationRedecl(PointOfInstantiation, TSK,
3887                                                    Var,
3888                                         MSInfo->getTemplateSpecializationKind(),
3889                                               MSInfo->getPointOfInstantiation(),
3890                                                    SuppressNew) ||
3891             SuppressNew)
3892           continue;
3893
3894         if (TSK == TSK_ExplicitInstantiationDefinition) {
3895           // C++0x [temp.explicit]p8:
3896           //   An explicit instantiation definition that names a class template
3897           //   specialization explicitly instantiates the class template
3898           //   specialization and is only an explicit instantiation definition
3899           //   of members whose definition is visible at the point of
3900           //   instantiation.
3901           if (!Var->getInstantiatedFromStaticDataMember()->getDefinition())
3902             continue;
3903
3904           Var->setTemplateSpecializationKind(TSK, PointOfInstantiation);
3905           InstantiateVariableDefinition(PointOfInstantiation, Var);
3906         } else {
3907           Var->setTemplateSpecializationKind(TSK, PointOfInstantiation);
3908         }
3909       }
3910     } else if (auto *Record = dyn_cast<CXXRecordDecl>(D)) {
3911       if (Record->hasAttr<ExcludeFromExplicitInstantiationAttr>())
3912         continue;
3913
3914       // Always skip the injected-class-name, along with any
3915       // redeclarations of nested classes, since both would cause us
3916       // to try to instantiate the members of a class twice.
3917       // Skip closure types; they'll get instantiated when we instantiate
3918       // the corresponding lambda-expression.
3919       if (Record->isInjectedClassName() || Record->getPreviousDecl() ||
3920           Record->isLambda())
3921         continue;
3922
3923       MemberSpecializationInfo *MSInfo = Record->getMemberSpecializationInfo();
3924       assert(MSInfo && "No member specialization information?");
3925
3926       if (MSInfo->getTemplateSpecializationKind()
3927                                                 == TSK_ExplicitSpecialization)
3928         continue;
3929
3930       if (Context.getTargetInfo().getTriple().isOSWindows() &&
3931           TSK == TSK_ExplicitInstantiationDeclaration) {
3932         // On Windows, explicit instantiation decl of the outer class doesn't
3933         // affect the inner class. Typically extern template declarations are
3934         // used in combination with dll import/export annotations, but those
3935         // are not propagated from the outer class templates to inner classes.
3936         // Therefore, do not instantiate inner classes on this platform, so
3937         // that users don't end up with undefined symbols during linking.
3938         continue;
3939       }
3940
3941       if (CheckSpecializationInstantiationRedecl(PointOfInstantiation, TSK,
3942                                                  Record,
3943                                         MSInfo->getTemplateSpecializationKind(),
3944                                               MSInfo->getPointOfInstantiation(),
3945                                                  SuppressNew) ||
3946           SuppressNew)
3947         continue;
3948
3949       CXXRecordDecl *Pattern = Record->getInstantiatedFromMemberClass();
3950       assert(Pattern && "Missing instantiated-from-template information");
3951
3952       if (!Record->getDefinition()) {
3953         if (!Pattern->getDefinition()) {
3954           // C++0x [temp.explicit]p8:
3955           //   An explicit instantiation definition that names a class template
3956           //   specialization explicitly instantiates the class template
3957           //   specialization and is only an explicit instantiation definition
3958           //   of members whose definition is visible at the point of
3959           //   instantiation.
3960           if (TSK == TSK_ExplicitInstantiationDeclaration) {
3961             MSInfo->setTemplateSpecializationKind(TSK);
3962             MSInfo->setPointOfInstantiation(PointOfInstantiation);
3963           }
3964
3965           continue;
3966         }
3967
3968         InstantiateClass(PointOfInstantiation, Record, Pattern,
3969                          TemplateArgs,
3970                          TSK);
3971       } else {
3972         if (TSK == TSK_ExplicitInstantiationDefinition &&
3973             Record->getTemplateSpecializationKind() ==
3974                 TSK_ExplicitInstantiationDeclaration) {
3975           Record->setTemplateSpecializationKind(TSK);
3976           MarkVTableUsed(PointOfInstantiation, Record, true);
3977         }
3978       }
3979
3980       Pattern = cast_or_null<CXXRecordDecl>(Record->getDefinition());
3981       if (Pattern)
3982         InstantiateClassMembers(PointOfInstantiation, Pattern, TemplateArgs,
3983                                 TSK);
3984     } else if (auto *Enum = dyn_cast<EnumDecl>(D)) {
3985       MemberSpecializationInfo *MSInfo = Enum->getMemberSpecializationInfo();
3986       assert(MSInfo && "No member specialization information?");
3987
3988       if (MSInfo->getTemplateSpecializationKind()
3989             == TSK_ExplicitSpecialization)
3990         continue;
3991
3992       if (CheckSpecializationInstantiationRedecl(
3993             PointOfInstantiation, TSK, Enum,
3994             MSInfo->getTemplateSpecializationKind(),
3995             MSInfo->getPointOfInstantiation(), SuppressNew) ||
3996           SuppressNew)
3997         continue;
3998
3999       if (Enum->getDefinition())
4000         continue;
4001
4002       EnumDecl *Pattern = Enum->getTemplateInstantiationPattern();
4003       assert(Pattern && "Missing instantiated-from-template information");
4004
4005       if (TSK == TSK_ExplicitInstantiationDefinition) {
4006         if (!Pattern->getDefinition())
4007           continue;
4008
4009         InstantiateEnum(PointOfInstantiation, Enum, Pattern, TemplateArgs, TSK);
4010       } else {
4011         MSInfo->setTemplateSpecializationKind(TSK);
4012         MSInfo->setPointOfInstantiation(PointOfInstantiation);
4013       }
4014     } else if (auto *Field = dyn_cast<FieldDecl>(D)) {
4015       // No need to instantiate in-class initializers during explicit
4016       // instantiation.
4017       if (Field->hasInClassInitializer() && TSK == TSK_ImplicitInstantiation) {
4018         CXXRecordDecl *ClassPattern =
4019             Instantiation->getTemplateInstantiationPattern();
4020         DeclContext::lookup_result Lookup =
4021             ClassPattern->lookup(Field->getDeclName());
4022         FieldDecl *Pattern = Lookup.find_first<FieldDecl>();
4023         assert(Pattern);
4024         InstantiateInClassInitializer(PointOfInstantiation, Field, Pattern,
4025                                       TemplateArgs);
4026       }
4027     }
4028   }
4029 }
4030
4031 /// Instantiate the definitions of all of the members of the
4032 /// given class template specialization, which was named as part of an
4033 /// explicit instantiation.
4034 void
4035 Sema::InstantiateClassTemplateSpecializationMembers(
4036                                            SourceLocation PointOfInstantiation,
4037                             ClassTemplateSpecializationDecl *ClassTemplateSpec,
4038                                                TemplateSpecializationKind TSK) {
4039   // C++0x [temp.explicit]p7:
4040   //   An explicit instantiation that names a class template
4041   //   specialization is an explicit instantion of the same kind
4042   //   (declaration or definition) of each of its members (not
4043   //   including members inherited from base classes) that has not
4044   //   been previously explicitly specialized in the translation unit
4045   //   containing the explicit instantiation, except as described
4046   //   below.
4047   InstantiateClassMembers(PointOfInstantiation, ClassTemplateSpec,
4048                           getTemplateInstantiationArgs(ClassTemplateSpec),
4049                           TSK);
4050 }
4051
4052 StmtResult
4053 Sema::SubstStmt(Stmt *S, const MultiLevelTemplateArgumentList &TemplateArgs) {
4054   if (!S)
4055     return S;
4056
4057   TemplateInstantiator Instantiator(*this, TemplateArgs,
4058                                     SourceLocation(),
4059                                     DeclarationName());
4060   return Instantiator.TransformStmt(S);
4061 }
4062
4063 bool Sema::SubstTemplateArguments(
4064     ArrayRef<TemplateArgumentLoc> Args,
4065     const MultiLevelTemplateArgumentList &TemplateArgs,
4066     TemplateArgumentListInfo &Out) {
4067   TemplateInstantiator Instantiator(*this, TemplateArgs, SourceLocation(),
4068                                     DeclarationName());
4069   return Instantiator.TransformTemplateArguments(Args.begin(), Args.end(), Out);
4070 }
4071
4072 ExprResult
4073 Sema::SubstExpr(Expr *E, const MultiLevelTemplateArgumentList &TemplateArgs) {
4074   if (!E)
4075     return E;
4076
4077   TemplateInstantiator Instantiator(*this, TemplateArgs,
4078                                     SourceLocation(),
4079                                     DeclarationName());
4080   return Instantiator.TransformExpr(E);
4081 }
4082
4083 ExprResult
4084 Sema::SubstConstraintExpr(Expr *E,
4085                           const MultiLevelTemplateArgumentList &TemplateArgs) {
4086   if (!E)
4087     return E;
4088
4089   // This is where we need to make sure we 'know' constraint checking needs to
4090   // happen.
4091   TemplateInstantiator Instantiator(*this, TemplateArgs, SourceLocation(),
4092                                     DeclarationName());
4093   return Instantiator.TransformExpr(E);
4094 }
4095
4096 ExprResult Sema::SubstInitializer(Expr *Init,
4097                           const MultiLevelTemplateArgumentList &TemplateArgs,
4098                           bool CXXDirectInit) {
4099   TemplateInstantiator Instantiator(*this, TemplateArgs, SourceLocation(),
4100                                     DeclarationName());
4101   return Instantiator.TransformInitializer(Init, CXXDirectInit);
4102 }
4103
4104 bool Sema::SubstExprs(ArrayRef<Expr *> Exprs, bool IsCall,
4105                       const MultiLevelTemplateArgumentList &TemplateArgs,
4106                       SmallVectorImpl<Expr *> &Outputs) {
4107   if (Exprs.empty())
4108     return false;
4109
4110   TemplateInstantiator Instantiator(*this, TemplateArgs,
4111                                     SourceLocation(),
4112                                     DeclarationName());
4113   return Instantiator.TransformExprs(Exprs.data(), Exprs.size(),
4114                                      IsCall, Outputs);
4115 }
4116
4117 NestedNameSpecifierLoc
4118 Sema::SubstNestedNameSpecifierLoc(NestedNameSpecifierLoc NNS,
4119                         const MultiLevelTemplateArgumentList &TemplateArgs) {
4120   if (!NNS)
4121     return NestedNameSpecifierLoc();
4122
4123   TemplateInstantiator Instantiator(*this, TemplateArgs, NNS.getBeginLoc(),
4124                                     DeclarationName());
4125   return Instantiator.TransformNestedNameSpecifierLoc(NNS);
4126 }
4127
4128 /// Do template substitution on declaration name info.
4129 DeclarationNameInfo
4130 Sema::SubstDeclarationNameInfo(const DeclarationNameInfo &NameInfo,
4131                          const MultiLevelTemplateArgumentList &TemplateArgs) {
4132   TemplateInstantiator Instantiator(*this, TemplateArgs, NameInfo.getLoc(),
4133                                     NameInfo.getName());
4134   return Instantiator.TransformDeclarationNameInfo(NameInfo);
4135 }
4136
4137 TemplateName
4138 Sema::SubstTemplateName(NestedNameSpecifierLoc QualifierLoc,
4139                         TemplateName Name, SourceLocation Loc,
4140                         const MultiLevelTemplateArgumentList &TemplateArgs) {
4141   TemplateInstantiator Instantiator(*this, TemplateArgs, Loc,
4142                                     DeclarationName());
4143   CXXScopeSpec SS;
4144   SS.Adopt(QualifierLoc);
4145   return Instantiator.TransformTemplateName(SS, Name, Loc);
4146 }
4147
4148 static const Decl *getCanonicalParmVarDecl(const Decl *D) {
4149   // When storing ParmVarDecls in the local instantiation scope, we always
4150   // want to use the ParmVarDecl from the canonical function declaration,
4151   // since the map is then valid for any redeclaration or definition of that
4152   // function.
4153   if (const ParmVarDecl *PV = dyn_cast<ParmVarDecl>(D)) {
4154     if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(PV->getDeclContext())) {
4155       unsigned i = PV->getFunctionScopeIndex();
4156       // This parameter might be from a freestanding function type within the
4157       // function and isn't necessarily referring to one of FD's parameters.
4158       if (i < FD->getNumParams() && FD->getParamDecl(i) == PV)
4159         return FD->getCanonicalDecl()->getParamDecl(i);
4160     }
4161   }
4162   return D;
4163 }
4164
4165
4166 llvm::PointerUnion<Decl *, LocalInstantiationScope::DeclArgumentPack *> *
4167 LocalInstantiationScope::findInstantiationOf(const Decl *D) {
4168   D = getCanonicalParmVarDecl(D);
4169   for (LocalInstantiationScope *Current = this; Current;
4170        Current = Current->Outer) {
4171
4172     // Check if we found something within this scope.
4173     const Decl *CheckD = D;
4174     do {
4175       LocalDeclsMap::iterator Found = Current->LocalDecls.find(CheckD);
4176       if (Found != Current->LocalDecls.end())
4177         return &Found->second;
4178
4179       // If this is a tag declaration, it's possible that we need to look for
4180       // a previous declaration.
4181       if (const TagDecl *Tag = dyn_cast<TagDecl>(CheckD))
4182         CheckD = Tag->getPreviousDecl();
4183       else
4184         CheckD = nullptr;
4185     } while (CheckD);
4186
4187     // If we aren't combined with our outer scope, we're done.
4188     if (!Current->CombineWithOuterScope)
4189       break;
4190   }
4191
4192   // If we're performing a partial substitution during template argument
4193   // deduction, we may not have values for template parameters yet.
4194   if (isa<NonTypeTemplateParmDecl>(D) || isa<TemplateTypeParmDecl>(D) ||
4195       isa<TemplateTemplateParmDecl>(D))
4196     return nullptr;
4197
4198   // Local types referenced prior to definition may require instantiation.
4199   if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D))
4200     if (RD->isLocalClass())
4201       return nullptr;
4202
4203   // Enumeration types referenced prior to definition may appear as a result of
4204   // error recovery.
4205   if (isa<EnumDecl>(D))
4206     return nullptr;
4207
4208   // Materialized typedefs/type alias for implicit deduction guides may require
4209   // instantiation.
4210   if (isa<TypedefNameDecl>(D) &&
4211       isa<CXXDeductionGuideDecl>(D->getDeclContext()))
4212     return nullptr;
4213
4214   // If we didn't find the decl, then we either have a sema bug, or we have a
4215   // forward reference to a label declaration.  Return null to indicate that
4216   // we have an uninstantiated label.
4217   assert(isa<LabelDecl>(D) && "declaration not instantiated in this scope");
4218   return nullptr;
4219 }
4220
4221 void LocalInstantiationScope::InstantiatedLocal(const Decl *D, Decl *Inst) {
4222   D = getCanonicalParmVarDecl(D);
4223   llvm::PointerUnion<Decl *, DeclArgumentPack *> &Stored = LocalDecls[D];
4224   if (Stored.isNull()) {
4225 #ifndef NDEBUG
4226     // It should not be present in any surrounding scope either.
4227     LocalInstantiationScope *Current = this;
4228     while (Current->CombineWithOuterScope && Current->Outer) {
4229       Current = Current->Outer;
4230       assert(!Current->LocalDecls.contains(D) &&
4231              "Instantiated local in inner and outer scopes");
4232     }
4233 #endif
4234     Stored = Inst;
4235   } else if (DeclArgumentPack *Pack = Stored.dyn_cast<DeclArgumentPack *>()) {
4236     Pack->push_back(cast<VarDecl>(Inst));
4237   } else {
4238     assert(Stored.get<Decl *>() == Inst && "Already instantiated this local");
4239   }
4240 }
4241
4242 void LocalInstantiationScope::InstantiatedLocalPackArg(const Decl *D,
4243                                                        VarDecl *Inst) {
4244   D = getCanonicalParmVarDecl(D);
4245   DeclArgumentPack *Pack = LocalDecls[D].get<DeclArgumentPack *>();
4246   Pack->push_back(Inst);
4247 }
4248
4249 void LocalInstantiationScope::MakeInstantiatedLocalArgPack(const Decl *D) {
4250 #ifndef NDEBUG
4251   // This should be the first time we've been told about this decl.
4252   for (LocalInstantiationScope *Current = this;
4253        Current && Current->CombineWithOuterScope; Current = Current->Outer)
4254     assert(!Current->LocalDecls.contains(D) &&
4255            "Creating local pack after instantiation of local");
4256 #endif
4257
4258   D = getCanonicalParmVarDecl(D);
4259   llvm::PointerUnion<Decl *, DeclArgumentPack *> &Stored = LocalDecls[D];
4260   DeclArgumentPack *Pack = new DeclArgumentPack;
4261   Stored = Pack;
4262   ArgumentPacks.push_back(Pack);
4263 }
4264
4265 bool LocalInstantiationScope::isLocalPackExpansion(const Decl *D) {
4266   for (DeclArgumentPack *Pack : ArgumentPacks)
4267     if (llvm::is_contained(*Pack, D))
4268       return true;
4269   return false;
4270 }
4271
4272 void LocalInstantiationScope::SetPartiallySubstitutedPack(NamedDecl *Pack,
4273                                           const TemplateArgument *ExplicitArgs,
4274                                                     unsigned NumExplicitArgs) {
4275   assert((!PartiallySubstitutedPack || PartiallySubstitutedPack == Pack) &&
4276          "Already have a partially-substituted pack");
4277   assert((!PartiallySubstitutedPack
4278           || NumArgsInPartiallySubstitutedPack == NumExplicitArgs) &&
4279          "Wrong number of arguments in partially-substituted pack");
4280   PartiallySubstitutedPack = Pack;
4281   ArgsInPartiallySubstitutedPack = ExplicitArgs;
4282   NumArgsInPartiallySubstitutedPack = NumExplicitArgs;
4283 }
4284
4285 NamedDecl *LocalInstantiationScope::getPartiallySubstitutedPack(
4286                                          const TemplateArgument **ExplicitArgs,
4287                                               unsigned *NumExplicitArgs) const {
4288   if (ExplicitArgs)
4289     *ExplicitArgs = nullptr;
4290   if (NumExplicitArgs)
4291     *NumExplicitArgs = 0;
4292
4293   for (const LocalInstantiationScope *Current = this; Current;
4294        Current = Current->Outer) {
4295     if (Current->PartiallySubstitutedPack) {
4296       if (ExplicitArgs)
4297         *ExplicitArgs = Current->ArgsInPartiallySubstitutedPack;
4298       if (NumExplicitArgs)
4299         *NumExplicitArgs = Current->NumArgsInPartiallySubstitutedPack;
4300
4301       return Current->PartiallySubstitutedPack;
4302     }
4303
4304     if (!Current->CombineWithOuterScope)
4305       break;
4306   }
4307
4308   return nullptr;
4309 }