clang-tools-extra/clang-tidy/misc/MisplacedConstCheck.cpp

   1 //===--- MisplacedConstCheck.cpp - clang-tidy------------------------------===//
   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 "MisplacedConstCheck.h"
  10 #include "clang/AST/ASTContext.h"
  11 #include "clang/ASTMatchers/ASTMatchFinder.h"
  12
  13 using namespace clang::ast_matchers;
  14
  15 namespace clang::tidy::misc {
  16
  17 void MisplacedConstCheck::registerMatchers(MatchFinder *Finder) {
  18   auto NonConstAndNonFunctionPointerType = hasType(pointerType(unless(
  19       pointee(anyOf(isConstQualified(), ignoringParens(functionType()))))));
  20
  21   Finder->addMatcher(
  22       valueDecl(hasType(qualType(
  23                     isConstQualified(),
  24                     elaboratedType(namesType(typedefType(hasDeclaration(
  25                         anyOf(typedefDecl(NonConstAndNonFunctionPointerType)
  26                                   .bind("typedef"),
  27                               typeAliasDecl(NonConstAndNonFunctionPointerType)
  28                                   .bind("typeAlias")))))))))
  29           .bind("decl"),
  30       this);
  31 }
  32
  33 static QualType guessAlternateQualification(ASTContext &Context, QualType QT) {
  34   // We're given a QualType from a typedef where the qualifiers apply to the
  35   // pointer instead of the pointee. Strip the const qualifier from the pointer
  36   // type and add it to the pointee instead.
  37   if (!QT->isPointerType())
  38     return QT;
  39
  40   Qualifiers Quals = QT.getLocalQualifiers();
  41   Quals.removeConst();
  42
  43   QualType NewQT = Context.getPointerType(
  44       QualType(QT->getPointeeType().getTypePtr(), Qualifiers::Const));
  45   return NewQT.withCVRQualifiers(Quals.getCVRQualifiers());
  46 }
  47
  48 void MisplacedConstCheck::check(const MatchFinder::MatchResult &Result) {
  49   const auto *Var = Result.Nodes.getNodeAs<ValueDecl>("decl");
  50   ASTContext &Ctx = *Result.Context;
  51   QualType CanQT = Var->getType().getCanonicalType();
  52
  53   SourceLocation AliasLoc;
  54   const char *AliasType = nullptr;
  55   if (const auto *Typedef = Result.Nodes.getNodeAs<TypedefDecl>("typedef")) {
  56     AliasLoc = Typedef->getLocation();
  57     AliasType = "typedef";
  58   } else if (const auto *TypeAlias =
  59                  Result.Nodes.getNodeAs<TypeAliasDecl>("typeAlias")) {
  60     AliasLoc = TypeAlias->getLocation();
  61     AliasType = "type alias";
  62   } else {
  63     llvm_unreachable("registerMatchers has registered an unknown matcher,"
  64                      " code out of sync");
  65   }
  66
  67   diag(Var->getLocation(), "%0 declared with a const-qualified %1; "
  68                            "results in the type being '%2' instead of '%3'")
  69       << Var << AliasType << CanQT.getAsString(Ctx.getPrintingPolicy())
  70       << guessAlternateQualification(Ctx, CanQT)
  71              .getAsString(Ctx.getPrintingPolicy());
  72   diag(AliasLoc, "%0 declared here", DiagnosticIDs::Note) << AliasType;
  73 }
  74
  75 } // namespace clang::tidy::misc