Implement clang tool that converts std::string("") to std::string().

tools/clang/empty_string/EmptyStringConverter.cpp

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// 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.

[Nico, 2013/04/02 21:37:29]

Either this or run_tool.py should have an example command line at the top. ("Use
like this: $command")

+
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/ASTMatchers/ASTMatchFinder.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 clang::ast_matchers::MatchFinder;
+using clang::ast_matchers::argumentCountIs;
+using clang::ast_matchers::bindTemporaryExpr;
+using clang::ast_matchers::constructorDecl;
+using clang::ast_matchers::constructExpr;
+using clang::ast_matchers::defaultArgExpr;
+using clang::ast_matchers::expr;
+using clang::ast_matchers::forEach;
+using clang::ast_matchers::has;
+using clang::ast_matchers::hasArgument;
+using clang::ast_matchers::hasDeclaration;
+using clang::ast_matchers::hasName;
+using clang::ast_matchers::id;
+using clang::ast_matchers::methodDecl;
+using clang::ast_matchers::newExpr;
+using clang::ast_matchers::ofClass;
+using clang::ast_matchers::stringLiteral;
+using clang::ast_matchers::varDecl;
+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) LLVM_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) LLVM_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) LLVM_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 auto& constructor_call =
+      id("call",
+         constructExpr(
+             hasDeclaration(methodDecl(ofClass(hasName("std::basic_string")))),
+             argumentCountIs(2),
+             hasArgument(0, id("literal", stringLiteral())),
+             hasArgument(1, defaultArgExpr())));
+
+  // 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(newExpr(has(constructor_call)),
+                           &constructor_callback_);
+  match_finder->addMatcher(bindTemporaryExpr(has(constructor_call)),
+                           &temporary_callback_);
+  match_finder->addMatcher(
+      constructorDecl(forEach(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->getParenRange());
+  replacements_->insert(Replacement(*result.SourceManager, range, ""));
+}
+
+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");
+  replacements_->insert(Replacement(*result.SourceManager, call, ""));
+}
+
+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.
+  clang::SourceRange range = call->getParenRange();
+  if (range.isValid()) {
+    replacements_->insert(Replacement(*result.SourceManager, literal, ""));
+  } else {
+    replacements_->insert(
+        Replacement(*result.SourceManager, call, "std::string()"));
+  }
+}
+
+}  // namespace
+
+static llvm::cl::extrahelp common_help(CommonOptionsParser::HelpMessage);
+
+int main(int argc, const char* argv[]) {
+  CommonOptionsParser options(argc, argv);
+  clang::tooling::ClangTool tool(options.getCompilations(),
+                                 options.getSourcePathList());
+
+  Replacements replacements;
+  EmptyStringConverter converter(&replacements);
+  MatchFinder match_finder;
+  converter.SetupMatchers(&match_finder);
+
+  int result =
+      tool.run(clang::tooling::newFrontendActionFactory(&match_finder));
+  if (result != 0)
+    return result;
+
+  // 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.
+  llvm::outs() << "==== BEGIN EDITS ====\n";
+  for (const Replacement& r : replacements) {
+    llvm::outs() << "r:" << r.getFilePath() << ":" << r.getOffset() << ":"
+                 << r.getLength() << ":" << r.getReplacementText() << "\n";
+  }
+  llvm::outs() << "==== END EDITS ====\n";
+
+  return 0;
+}