StrCatAppendCheck.cpp
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//===--- StrCatAppendCheck.cpp - clang-tidy--------------------------------===//
//
// 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 "StrCatAppendCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
using namespace clang::ast_matchers;
namespace clang {
namespace tidy {
namespace abseil {
namespace {
// Skips any combination of temporary materialization, temporary binding and
// implicit casting.
AST_MATCHER_P(Stmt, IgnoringTemporaries, ast_matchers::internal::Matcher<Stmt>,
InnerMatcher) {
const Stmt *E = &Node;
while (true) {
if (const auto *MTE = dyn_cast<MaterializeTemporaryExpr>(E))
E = MTE->getSubExpr();
if (const auto *BTE = dyn_cast<CXXBindTemporaryExpr>(E))
E = BTE->getSubExpr();
if (const auto *ICE = dyn_cast<ImplicitCastExpr>(E))
E = ICE->getSubExpr();
else
break;
}
return InnerMatcher.matches(*E, Finder, Builder);
}
} // namespace
// TODO: str += StrCat(...)
// str.append(StrCat(...))
void StrCatAppendCheck::registerMatchers(MatchFinder *Finder) {
const auto StrCat = functionDecl(hasName("::absl::StrCat"));
// The arguments of absl::StrCat are implicitly converted to AlphaNum. This
// matches to the arguments because of that behavior.
const auto AlphaNum = IgnoringTemporaries(cxxConstructExpr(
argumentCountIs(1), hasType(cxxRecordDecl(hasName("::absl::AlphaNum"))),
hasArgument(0, ignoringImpCasts(declRefExpr(to(equalsBoundNode("LHS")),
expr().bind("Arg0"))))));
const auto HasAnotherReferenceToLhs =
callExpr(hasAnyArgument(expr(hasDescendant(declRefExpr(
to(equalsBoundNode("LHS")), unless(equalsBoundNode("Arg0")))))));
// Now look for calls to operator= with an object on the LHS and a call to
// StrCat on the RHS. The first argument of the StrCat call should be the same
// as the LHS. Ignore calls from template instantiations.
Finder->addMatcher(
traverse(ast_type_traits::TK_AsIs,
cxxOperatorCallExpr(
unless(isInTemplateInstantiation()),
hasOverloadedOperatorName("="),
hasArgument(0, declRefExpr(to(decl().bind("LHS")))),
hasArgument(
1, IgnoringTemporaries(
callExpr(callee(StrCat), hasArgument(0, AlphaNum),
unless(HasAnotherReferenceToLhs))
.bind("Call"))))
.bind("Op")),
this);
}
void StrCatAppendCheck::check(const MatchFinder::MatchResult &Result) {
const auto *Op = Result.Nodes.getNodeAs<CXXOperatorCallExpr>("Op");
const auto *Call = Result.Nodes.getNodeAs<CallExpr>("Call");
assert(Op != nullptr && Call != nullptr && "Matcher does not work as expected");
// Handles the case 'x = absl::StrCat(x)', which has no effect.
if (Call->getNumArgs() == 1) {
diag(Op->getBeginLoc(), "call to 'absl::StrCat' has no effect");
return;
}
// Emit a warning and emit fixits to go from
// x = absl::StrCat(x, ...)
// to
// absl::StrAppend(&x, ...)
diag(Op->getBeginLoc(),
"call 'absl::StrAppend' instead of 'absl::StrCat' when appending to a "
"string to avoid a performance penalty")
<< FixItHint::CreateReplacement(
CharSourceRange::getTokenRange(Op->getBeginLoc(),
Call->getCallee()->getEndLoc()),
"absl::StrAppend")
<< FixItHint::CreateInsertion(Call->getArg(0)->getBeginLoc(), "&");
}
} // namespace abseil
} // namespace tidy
} // namespace clang