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// Copyright 2013 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// This implements a Clang tool to convert all instances of std::string("") to
// std::string(). The latter is more efficient (as std::string doesn't have to
// take a copy of an empty string) and generates fewer instructions as well. It
// should be run using the tools/clang/scripts/run_tool.py helper.
#include <memory>
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/ASTMatchers/ASTMatchers.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Frontend/FrontendActions.h"
#include "clang/Tooling/CommonOptionsParser.h"
#include "clang/Tooling/Refactoring.h"
#include "clang/Tooling/Tooling.h"
#include "llvm/Support/CommandLine.h"
using namespace clang::ast_matchers;
using clang::tooling::CommonOptionsParser;
using clang::tooling::Replacement;
using clang::tooling::Replacements;
namespace {
// Handles replacements for stack and heap-allocated instances, e.g.:
// std::string a("");
// std::string* b = new std::string("");
class ConstructorCallback : public MatchFinder::MatchCallback {
public:
ConstructorCallback(Replacements* replacements)
: replacements_(replacements) {}
virtual void run(const MatchFinder::MatchResult& result) override;
private:
Replacements* const replacements_;
};
// Handles replacements for invocations of std::string("") in an initializer
// list.
class InitializerCallback : public MatchFinder::MatchCallback {
public:
InitializerCallback(Replacements* replacements)
: replacements_(replacements) {}
virtual void run(const MatchFinder::MatchResult& result) override;
private:
Replacements* const replacements_;
};
// Handles replacements for invocations of std::string("") in a temporary
// context, e.g. FunctionThatTakesString(std::string("")). Note that this
// handles implicits construction of std::string as well.
class TemporaryCallback : public MatchFinder::MatchCallback {
public:
TemporaryCallback(Replacements* replacements) : replacements_(replacements) {}
virtual void run(const MatchFinder::MatchResult& result) override;
private:
Replacements* const replacements_;
};
class EmptyStringConverter {
public:
explicit EmptyStringConverter(Replacements* replacements)
: constructor_callback_(replacements),
initializer_callback_(replacements),
temporary_callback_(replacements) {}
void SetupMatchers(MatchFinder* match_finder);
private:
ConstructorCallback constructor_callback_;
InitializerCallback initializer_callback_;
TemporaryCallback temporary_callback_;
};
void EmptyStringConverter::SetupMatchers(MatchFinder* match_finder) {
const clang::ast_matchers::StatementMatcher& constructor_call =
cxxConstructExpr(
hasDeclaration(cxxMethodDecl(ofClass(hasName("std::basic_string")))),
argumentCountIs(2), hasArgument(0, stringLiteral().bind("literal")),
hasArgument(1, cxxDefaultArgExpr()))
.bind("call");
// Note that expr(has()) in the matcher is significant; the Clang AST wraps
// calls to the std::string constructor with exprWithCleanups nodes. Without
// the expr(has()) matcher, the first and last rules would not match anything!
match_finder->addMatcher(varDecl(forEach(expr(has(constructor_call)))),
&constructor_callback_);
match_finder->addMatcher(cxxNewExpr(has(constructor_call)),
&constructor_callback_);
// The implicitly generated constructor for temporary could be wrapped by
// implicitCastExpr, so ignoringParenImpCasts is needed.
match_finder->addMatcher(
cxxBindTemporaryExpr(ignoringParenImpCasts(forEach(constructor_call))),
&temporary_callback_);
// Note that forEachConstructorInitializer is needed. The std::string
// constructor is wrapped by exprWithCleanups and cxxCtorInitializer.
// forEach() would not work.
match_finder->addMatcher(cxxConstructorDecl(forEachConstructorInitializer(
withInitializer(expr(has(constructor_call))))),
&initializer_callback_);
}
void ConstructorCallback::run(const MatchFinder::MatchResult& result) {
const clang::StringLiteral* literal =
result.Nodes.getNodeAs<clang::StringLiteral>("literal");
if (literal->getLength() > 0)
return;
const clang::CXXConstructExpr* call =
result.Nodes.getNodeAs<clang::CXXConstructExpr>("call");
clang::CharSourceRange range =
clang::CharSourceRange::getTokenRange(call->getParenOrBraceRange());
auto err = replacements_->add(Replacement(*result.SourceManager, range, ""));
assert(!err);
}
void InitializerCallback::run(const MatchFinder::MatchResult& result) {
const clang::StringLiteral* literal =
result.Nodes.getNodeAs<clang::StringLiteral>("literal");
if (literal->getLength() > 0)
return;
const clang::CXXConstructExpr* call =
result.Nodes.getNodeAs<clang::CXXConstructExpr>("call");
auto err = replacements_->add(Replacement(*result.SourceManager, call, ""));
assert(!err);
}
void TemporaryCallback::run(const MatchFinder::MatchResult& result) {
const clang::StringLiteral* literal =
result.Nodes.getNodeAs<clang::StringLiteral>("literal");
if (literal->getLength() > 0)
return;
const clang::CXXConstructExpr* call =
result.Nodes.getNodeAs<clang::CXXConstructExpr>("call");
// Differentiate between explicit and implicit calls to std::string's
// constructor. An implicitly generated constructor won't have a valid
// source range for the parenthesis. We do this because the matched expression
// for |call| in the explicit case doesn't include the closing parenthesis.
clang::SourceRange range = call->getParenOrBraceRange();
if (range.isValid()) {
auto err =
replacements_->add(Replacement(*result.SourceManager, literal, ""));
assert(!err);
} else {
auto err = replacements_->add(
Replacement(*result.SourceManager, call,
literal->isWide() ? "std::wstring()" : "std::string()"));
assert(!err);
}
}
} // namespace
static llvm::cl::extrahelp common_help(CommonOptionsParser::HelpMessage);
int main(int argc, const char* argv[]) {
llvm::cl::OptionCategory category("EmptyString Tool");
CommonOptionsParser options(argc, argv, category);
clang::tooling::ClangTool tool(options.getCompilations(),
options.getSourcePathList());
Replacements replacements;
EmptyStringConverter converter(&replacements);
MatchFinder match_finder;
converter.SetupMatchers(&match_finder);
std::unique_ptr<clang::tooling::FrontendActionFactory> frontend_factory =
clang::tooling::newFrontendActionFactory(&match_finder);
int result = tool.run(frontend_factory.get());
if (result != 0)
return result;
if (replacements.empty())
return 0;
// Each replacement line should have the following format:
// r:<file path>:<offset>:<length>:<replacement text>
// Only the <replacement text> field can contain embedded ":" characters.
// TODO(dcheng): Use a more clever serialization. Ideally we'd use the YAML
// serialization and then use clang-apply-replacements, but that would require
// copying and pasting a larger amount of boilerplate for all Chrome clang
// tools.
llvm::outs() << "==== BEGIN EDITS ====\n";
for (const auto& r : replacements) {
llvm::outs() << "r:::" << r.getFilePath() << ":::" << r.getOffset()
<< ":::" << r.getLength() << ":::" << r.getReplacementText()
<< "\n";
}
llvm::outs() << "==== END EDITS ====\n";
return 0;
}
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