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//===--- AvoidCStyleCastsCheck.cpp - clang-tidy -----------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#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::tidy::google::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(isInTemplateInstantiation()))
.bind("cast"),
this);
Finder->addMatcher(
cxxFunctionalCastExpr(unless(hasDescendant(cxxConstructExpr())),
unless(hasDescendant(initListExpr())))
.bind("cast"),
this);
}
static bool needsConstCast(QualType SourceType, QualType DestType) {
while ((SourceType->isPointerType() && DestType->isPointerType()) ||
(SourceType->isReferenceType() && DestType->isReferenceType())) {
SourceType = SourceType->getPointeeType();
DestType = DestType->getPointeeType();
if (SourceType.isConstQualified() && !DestType.isConstQualified()) {
return (SourceType->isPointerType() == DestType->isPointerType()) &&
(SourceType->isReferenceType() == DestType->isReferenceType());
}
}
return false;
}
static bool pointedUnqualifiedTypesAreEqual(QualType T1, QualType T2) {
while ((T1->isPointerType() && T2->isPointerType()) ||
(T1->isReferenceType() && T2->isReferenceType())) {
T1 = T1->getPointeeType();
T2 = T2->getPointeeType();
}
return T1.getUnqualifiedType() == T2.getUnqualifiedType();
}
static clang::CharSourceRange getReplaceRange(const ExplicitCastExpr *Expr) {
if (const auto *CastExpr = dyn_cast<CStyleCastExpr>(Expr)) {
return CharSourceRange::getCharRange(
CastExpr->getLParenLoc(),
CastExpr->getSubExprAsWritten()->getBeginLoc());
} else if (const auto *CastExpr = dyn_cast<CXXFunctionalCastExpr>(Expr)) {
return CharSourceRange::getCharRange(CastExpr->getBeginLoc(),
CastExpr->getLParenLoc());
} else
llvm_unreachable("Unsupported CastExpr");
}
static StringRef getDestTypeString(const SourceManager &SM,
const LangOptions &LangOpts,
const ExplicitCastExpr *Expr) {
SourceLocation BeginLoc;
SourceLocation EndLoc;
if (const auto *CastExpr = dyn_cast<CStyleCastExpr>(Expr)) {
BeginLoc = CastExpr->getLParenLoc().getLocWithOffset(1);
EndLoc = CastExpr->getRParenLoc().getLocWithOffset(-1);
} else if (const auto *CastExpr = dyn_cast<CXXFunctionalCastExpr>(Expr)) {
BeginLoc = CastExpr->getBeginLoc();
EndLoc = CastExpr->getLParenLoc().getLocWithOffset(-1);
} else
llvm_unreachable("Unsupported CastExpr");
return Lexer::getSourceText(CharSourceRange::getTokenRange(BeginLoc, EndLoc),
SM, LangOpts);
}
void AvoidCStyleCastsCheck::check(const MatchFinder::MatchResult &Result) {
const auto *CastExpr = Result.Nodes.getNodeAs<ExplicitCastExpr>("cast");
// Ignore casts in macros.
if (CastExpr->getExprLoc().isMacroID())
return;
// Casting to void is an idiomatic way to mute "unused variable" and similar
// warnings.
if (CastExpr->getCastKind() == CK_ToVoid)
return;
auto IsFunction = [](QualType T) {
T = T.getCanonicalType().getNonReferenceType();
return T->isFunctionType() || T->isFunctionPointerType() ||
T->isMemberFunctionPointerType();
};
const QualType DestTypeAsWritten =
CastExpr->getTypeAsWritten().getUnqualifiedType();
const QualType SourceTypeAsWritten =
CastExpr->getSubExprAsWritten()->getType().getUnqualifiedType();
const QualType SourceType = SourceTypeAsWritten.getCanonicalType();
const QualType DestType = DestTypeAsWritten.getCanonicalType();
CharSourceRange ReplaceRange = getReplaceRange(CastExpr);
bool FnToFnCast =
IsFunction(SourceTypeAsWritten) && IsFunction(DestTypeAsWritten);
const bool ConstructorCast = !CastExpr->getTypeAsWritten().hasQualifiers() &&
DestTypeAsWritten->isRecordType() &&
!DestTypeAsWritten->isElaboratedTypeSpecifier();
if (CastExpr->getCastKind() == CK_NoOp && !FnToFnCast) {
// Function pointer/reference casts may be needed to resolve ambiguities in
// case of overloaded functions, so detection of redundant casts is trickier
// in this case. Don't emit "redundant cast" warnings for function
// pointer/reference types.
QualType Src = SourceTypeAsWritten, Dst = DestTypeAsWritten;
if (const auto *ElTy = dyn_cast<ElaboratedType>(Src))
Src = ElTy->getNamedType();
if (const auto *ElTy = dyn_cast<ElaboratedType>(Dst))
Dst = ElTy->getNamedType();
if (Src == Dst) {
diag(CastExpr->getBeginLoc(), "redundant cast to the same type")
<< FixItHint::CreateRemoval(ReplaceRange);
return;
}
}
// The rest of this check is only relevant to C++.
// We also disable it for Objective-C++.
if (!getLangOpts().CPlusPlus || getLangOpts().ObjC)
return;
// Ignore code inside extern "C" {} blocks.
if (!match(expr(hasAncestor(linkageSpecDecl())), *CastExpr, *Result.Context)
.empty())
return;
// Ignore code in .c files and headers included from them, even if they are
// compiled as C++.
if (getCurrentMainFile().endswith(".c"))
return;
SourceManager &SM = *Result.SourceManager;
// Ignore code in .c files #included in other files (which shouldn't be done,
// but people still do this for test and other purposes).
if (SM.getFilename(SM.getSpellingLoc(CastExpr->getBeginLoc())).endswith(".c"))
return;
// Leave type spelling exactly as it was (unlike
// getTypeAsWritten().getAsString() which would spell enum types 'enum X').
StringRef DestTypeString = getDestTypeString(SM, getLangOpts(), CastExpr);
auto Diag =
diag(CastExpr->getBeginLoc(), "C-style casts are discouraged; use %0");
auto ReplaceWithCast = [&](std::string CastText) {
const Expr *SubExpr = CastExpr->getSubExprAsWritten()->IgnoreImpCasts();
if (!isa<ParenExpr>(SubExpr) && !isa<CXXFunctionalCastExpr>(CastExpr)) {
CastText.push_back('(');
Diag << FixItHint::CreateInsertion(
Lexer::getLocForEndOfToken(SubExpr->getEndLoc(), 0, SM,
getLangOpts()),
")");
}
Diag << FixItHint::CreateReplacement(ReplaceRange, CastText);
};
auto ReplaceWithNamedCast = [&](StringRef CastType) {
Diag << CastType;
ReplaceWithCast((CastType + "<" + DestTypeString + ">").str());
};
auto ReplaceWithConstructorCall = [&]() {
Diag << "constructor call syntax";
// FIXME: Validate DestTypeString, maybe.
ReplaceWithCast(DestTypeString.str());
};
// Suggest appropriate C++ cast. See [expr.cast] for cast notation semantics.
switch (CastExpr->getCastKind()) {
case CK_FunctionToPointerDecay:
ReplaceWithNamedCast("static_cast");
return;
case CK_ConstructorConversion:
if (ConstructorCast) {
ReplaceWithConstructorCall();
} else {
ReplaceWithNamedCast("static_cast");
}
return;
case CK_NoOp:
if (FnToFnCast) {
ReplaceWithNamedCast("static_cast");
return;
}
if (SourceType == DestType) {
Diag << "static_cast (if needed, the cast may be redundant)";
ReplaceWithCast(("static_cast<" + DestTypeString + ">").str());
return;
}
if (needsConstCast(SourceType, DestType) &&
pointedUnqualifiedTypesAreEqual(SourceType, DestType)) {
ReplaceWithNamedCast("const_cast");
return;
}
if (ConstructorCast) {
ReplaceWithConstructorCall();
return;
}
if (DestType->isReferenceType()) {
QualType Dest = DestType.getNonReferenceType();
QualType Source = SourceType.getNonReferenceType();
if (Source == Dest.withConst() ||
SourceType.getNonReferenceType() == DestType.getNonReferenceType()) {
ReplaceWithNamedCast("const_cast");
return;
}
break;
}
[[fallthrough]];
case clang::CK_IntegralCast:
// Convert integral and no-op casts between builtin types and enums to
// static_cast. A cast from enum to integer may be unnecessary, but it's
// still retained.
if ((SourceType->isBuiltinType() || SourceType->isEnumeralType()) &&
(DestType->isBuiltinType() || DestType->isEnumeralType())) {
ReplaceWithNamedCast("static_cast");
return;
}
break;
case CK_BitCast:
// FIXME: Suggest const_cast<...>(reinterpret_cast<...>(...)) replacement.
if (!needsConstCast(SourceType, DestType)) {
if (SourceType->isVoidPointerType())
ReplaceWithNamedCast("static_cast");
else
ReplaceWithNamedCast("reinterpret_cast");
return;
}
break;
default:
break;
}
Diag << "static_cast/const_cast/reinterpret_cast";
}
} // namespace clang::tidy::google::readability
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