clang-tools-extra/clang-tidy/bugprone/ForwardDeclarationNamespaceCheck.cpp

   1 //===--- ForwardDeclarationNamespaceCheck.cpp - clang-tidy ------*- C++ -*-===//
   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
   9 #include "ForwardDeclarationNamespaceCheck.h"
  10 #include "clang/AST/ASTContext.h"
  11 #include "clang/AST/Decl.h"
  12 #include "clang/ASTMatchers/ASTMatchFinder.h"
  13 #include "clang/ASTMatchers/ASTMatchers.h"
  14 #include <stack>
  15 #include <string>
  16
  17 using namespace clang::ast_matchers;
  18
  19 namespace clang::tidy::bugprone {
  20
  21 void ForwardDeclarationNamespaceCheck::registerMatchers(MatchFinder *Finder) {
  22   // Match all class declarations/definitions *EXCEPT*
  23   // 1. implicit classes, e.g. `class A {};` has implicit `class A` inside `A`.
  24   // 2. nested classes declared/defined inside another class.
  25   // 3. template class declaration, template instantiation or
  26   //    specialization (NOTE: extern specialization is filtered out by
  27   //    `unless(hasAncestor(cxxRecordDecl()))`).
  28   auto IsInSpecialization = hasAncestor(
  29       decl(anyOf(cxxRecordDecl(isExplicitTemplateSpecialization()),
  30                  functionDecl(isExplicitTemplateSpecialization()))));
  31   Finder->addMatcher(
  32       cxxRecordDecl(
  33           hasParent(decl(anyOf(namespaceDecl(), translationUnitDecl()))),
  34           unless(isImplicit()), unless(hasAncestor(cxxRecordDecl())),
  35           unless(isInstantiated()), unless(IsInSpecialization),
  36           unless(classTemplateSpecializationDecl()))
  37           .bind("record_decl"),
  38       this);
  39
  40   // Match all friend declarations. Classes used in friend declarations are not
  41   // marked as referenced in AST. We need to record all record classes used in
  42   // friend declarations.
  43   Finder->addMatcher(friendDecl().bind("friend_decl"), this);
  44 }
  45
  46 void ForwardDeclarationNamespaceCheck::check(
  47     const MatchFinder::MatchResult &Result) {
  48   if (const auto *RecordDecl =
  49           Result.Nodes.getNodeAs<CXXRecordDecl>("record_decl")) {
  50     StringRef DeclName = RecordDecl->getName();
  51     if (RecordDecl->isThisDeclarationADefinition()) {
  52       DeclNameToDefinitions[DeclName].push_back(RecordDecl);
  53     } else {
  54       // If a declaration has no definition, the definition could be in another
  55       // namespace (a wrong namespace).
  56       // NOTE: even a declaration does have definition, we still need it to
  57       // compare with other declarations.
  58       DeclNameToDeclarations[DeclName].push_back(RecordDecl);
  59     }
  60   } else {
  61     const auto *Decl = Result.Nodes.getNodeAs<FriendDecl>("friend_decl");
  62     assert(Decl && "Decl is neither record_decl nor friend decl!");
  63
  64     // Classes used in friend declarations are not marked referenced in AST,
  65     // so we need to check classes used in friend declarations manually to
  66     // reduce the rate of false positive.
  67     // For example, in
  68     //    \code
  69     //      struct A;
  70     //      struct B { friend A; };
  71     //    \endcode
  72     // `A` will not be marked as "referenced" in the AST.
  73     if (const TypeSourceInfo *Tsi = Decl->getFriendType()) {
  74       QualType Desugared = Tsi->getType().getDesugaredType(*Result.Context);
  75       FriendTypes.insert(Desugared.getTypePtr());
  76     }
  77   }
  78 }
  79
  80 static bool haveSameNamespaceOrTranslationUnit(const CXXRecordDecl *Decl1,
  81                                                const CXXRecordDecl *Decl2) {
  82   const DeclContext *ParentDecl1 = Decl1->getLexicalParent();
  83   const DeclContext *ParentDecl2 = Decl2->getLexicalParent();
  84
  85   // Since we only matched declarations whose parent is Namespace or
  86   // TranslationUnit declaration, the parent should be either a translation unit
  87   // or namespace.
  88   if (ParentDecl1->getDeclKind() == Decl::TranslationUnit ||
  89       ParentDecl2->getDeclKind() == Decl::TranslationUnit) {
  90     return ParentDecl1 == ParentDecl2;
  91   }
  92   assert(ParentDecl1->getDeclKind() == Decl::Namespace &&
  93          "ParentDecl1 declaration must be a namespace");
  94   assert(ParentDecl2->getDeclKind() == Decl::Namespace &&
  95          "ParentDecl2 declaration must be a namespace");
  96   auto *Ns1 = NamespaceDecl::castFromDeclContext(ParentDecl1);
  97   auto *Ns2 = NamespaceDecl::castFromDeclContext(ParentDecl2);
  98   return Ns1->getOriginalNamespace() == Ns2->getOriginalNamespace();
  99 }
 100
 101 static std::string getNameOfNamespace(const CXXRecordDecl *Decl) {
 102   const auto *ParentDecl = Decl->getLexicalParent();
 103   if (ParentDecl->getDeclKind() == Decl::TranslationUnit) {
 104     return "(global)";
 105   }
 106   const auto *NsDecl = cast<NamespaceDecl>(ParentDecl);
 107   std::string Ns;
 108   llvm::raw_string_ostream OStream(Ns);
 109   NsDecl->printQualifiedName(OStream);
 110   OStream.flush();
 111   return Ns.empty() ? "(global)" : Ns;
 112 }
 113
 114 void ForwardDeclarationNamespaceCheck::onEndOfTranslationUnit() {
 115   // Iterate each group of declarations by name.
 116   for (const auto &KeyValuePair : DeclNameToDeclarations) {
 117     const auto &Declarations = KeyValuePair.second;
 118     // If more than 1 declaration exists, we check if all are in the same
 119     // namespace.
 120     for (const auto *CurDecl : Declarations) {
 121       if (CurDecl->hasDefinition() || CurDecl->isReferenced()) {
 122         continue; // Skip forward declarations that are used/referenced.
 123       }
 124       if (FriendTypes.contains(CurDecl->getTypeForDecl())) {
 125         continue; // Skip forward declarations referenced as friend.
 126       }
 127       if (CurDecl->getLocation().isMacroID() ||
 128           CurDecl->getLocation().isInvalid()) {
 129         continue;
 130       }
 131       // Compare with all other declarations with the same name.
 132       for (const auto *Decl : Declarations) {
 133         if (Decl == CurDecl) {
 134           continue; // Don't compare with self.
 135         }
 136         if (!CurDecl->hasDefinition() &&
 137             !haveSameNamespaceOrTranslationUnit(CurDecl, Decl)) {
 138           diag(CurDecl->getLocation(),
 139                "declaration %0 is never referenced, but a declaration with "
 140                "the same name found in another namespace '%1'")
 141               << CurDecl << getNameOfNamespace(Decl);
 142           diag(Decl->getLocation(), "a declaration of %0 is found here",
 143                DiagnosticIDs::Note)
 144               << Decl;
 145           break; // FIXME: We only generate one warning for each declaration.
 146         }
 147       }
 148       // Check if a definition in another namespace exists.
 149       const auto DeclName = CurDecl->getName();
 150       if (!DeclNameToDefinitions.contains(DeclName)) {
 151         continue; // No definition in this translation unit, we can skip it.
 152       }
 153       // Make a warning for each definition with the same name (in other
 154       // namespaces).
 155       const auto &Definitions = DeclNameToDefinitions[DeclName];
 156       for (const auto *Def : Definitions) {
 157         diag(CurDecl->getLocation(),
 158              "no definition found for %0, but a definition with "
 159              "the same name %1 found in another namespace '%2'")
 160             << CurDecl << Def << getNameOfNamespace(Def);
 161         diag(Def->getLocation(), "a definition of %0 is found here",
 162              DiagnosticIDs::Note)
 163             << Def;
 164       }
 165     }
 166   }
 167 }
 168
 169 } // namespace clang::tidy::bugprone