clang-tidy/google/AvoidCStyleCastsCheck.cpp

//===--- AvoidCStyleCastsCheck.cpp - clang-tidy -----------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "AvoidCStyleCastsCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/ASTMatchers/ASTMatchers.h"
#include "clang/Lex/Lexer.h"

using namespace clang::ast_matchers;

namespace clang {
namespace tidy {
namespace readability {

void
AvoidCStyleCastsCheck::registerMatchers(ast_matchers::MatchFinder *Finder) {
  Finder->addMatcher(
      cStyleCastExpr(
          // Filter out (EnumType)IntegerLiteral construct, which is generated
          // for non-type template arguments of enum types.
          // FIXME: Remove this once this is fixed in the AST.
          unless(hasParent(substNonTypeTemplateParmExpr())),
          // Avoid matches in template instantiations.
          unless(hasAncestor(decl(
              anyOf(recordDecl(ast_matchers::isTemplateInstantiation()),
                    functionDecl(ast_matchers::isTemplateInstantiation()))))))
          .bind("cast"),
      this);
}

bool needsConstCast(QualType SourceType, QualType DestType) {
  SourceType = SourceType.getNonReferenceType();
  DestType = DestType.getNonReferenceType();
  while (SourceType->isPointerType() && DestType->isPointerType()) {
    SourceType = SourceType->getPointeeType();
    DestType = DestType->getPointeeType();
    if (SourceType.isConstQualified() && !DestType.isConstQualified())
      return true;
  }
  return false;
}

bool pointedTypesAreEqual(QualType SourceType, QualType DestType) {
  SourceType = SourceType.getNonReferenceType();
  DestType = DestType.getNonReferenceType();
  while (SourceType->isPointerType() && DestType->isPointerType()) {
    SourceType = SourceType->getPointeeType();
    DestType = DestType->getPointeeType();
  }
  return SourceType.getUnqualifiedType() == DestType.getUnqualifiedType();
}

void AvoidCStyleCastsCheck::check(const MatchFinder::MatchResult &Result) {
  const auto *CastExpr = Result.Nodes.getNodeAs<CStyleCastExpr>("cast");

  // Casting to void is an idiomatic way to mute "unused variable" and similar
  // warnings.
  if (CastExpr->getTypeAsWritten()->isVoidType())
    return;

  QualType SourceType =
      CastExpr->getSubExprAsWritten()->getType().getCanonicalType();
  QualType DestType = CastExpr->getTypeAsWritten().getCanonicalType();

  auto ParenRange = CharSourceRange::getTokenRange(CastExpr->getLParenLoc(),
                                                   CastExpr->getRParenLoc());
  if (SourceType == DestType) {
    diag(CastExpr->getLocStart(), "Redundant cast to the same type.")
        << FixItHint::CreateRemoval(ParenRange);
    return;
  }

  std::string DestTypeString = CastExpr->getTypeAsWritten().getAsString();

  auto diag_builder =
      diag(CastExpr->getLocStart(), "C-style casts are discouraged. %0");

  auto ReplaceWithCast = [&](StringRef CastType) {
    diag_builder << ("Use " + CastType + ".").str();
    if (ParenRange.getBegin().isMacroID() || ParenRange.getEnd().isMacroID())
      return;

    const Expr *SubExpr = CastExpr->getSubExprAsWritten()->IgnoreImpCasts();
    std::string CastText = (CastType + "<" + DestTypeString + ">").str();
    if (!isa<ParenExpr>(SubExpr)) {
      CastText.push_back('(');
      diag_builder << FixItHint::CreateInsertion(
          Lexer::getLocForEndOfToken(SubExpr->getLocEnd(), 0,
                                     *Result.SourceManager,
                                     Result.Context->getLangOpts()),
          ")");
    }
    diag_builder << FixItHint::CreateReplacement(ParenRange, CastText);
  };
  // Suggest appropriate C++ cast. See [expr.cast] for cast notation semantics.
  switch (CastExpr->getCastKind()) {
  case CK_NoOp:
    if (needsConstCast(SourceType, DestType) &&
        pointedTypesAreEqual(SourceType, DestType)) {
      ReplaceWithCast("const_cast");
      return;
    }
    if (DestType->isReferenceType() &&
        (SourceType.getNonReferenceType() ==
             DestType.getNonReferenceType().withConst() ||
         SourceType.getNonReferenceType() == DestType.getNonReferenceType())) {
      ReplaceWithCast("const_cast");
      return;
    }
    if (SourceType->isBuiltinType() && DestType->isBuiltinType()) {
      ReplaceWithCast("static_cast");
      return;
    }
    break;
  case CK_BitCast:
    // FIXME: Suggest const_cast<...>(reinterpret_cast<...>(...)) replacement.
    if (!needsConstCast(SourceType, DestType)) {
      ReplaceWithCast("reinterpret_cast");
      return;
    }
    break;
  default:
    break;
  }

  diag_builder << "Use static_cast/const_cast/reinterpret_cast.";
}

} // namespace readability
} // namespace tidy
} // namespace clang