lib/Migrator/Migrator.cpp - third_party/swift - Git at Google

 //===--- Migrator.cpp -----------------------------------------------------===//
 // This source file is part of the Swift.org open source project
 //
 // Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 //
 //===----------------------------------------------------------------------===//

 #include "swift/Basic/Diff.h"
 #include "swift/Frontend/Frontend.h"
 #include "swift/Migrator/ASTMigratorPass.h"
 #include "swift/Migrator/EditorAdapter.h"
 #include "swift/Migrator/FixitApplyDiagnosticConsumer.h"
 #include "swift/Migrator/Migrator.h"
 #include "swift/Migrator/RewriteBufferEditsReceiver.h"
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Edit/EditedSource.h"
 #include "clang/Rewrite/Core/RewriteBuffer.h"
 #include "llvm/Support/FileSystem.h"

 using namespace swift;
 using namespace swift::migrator;

 bool migrator::updateCodeAndEmitRemapIfNeeded(
     CompilerInstance *Instance, const CompilerInvocation &Invocation) {
   if (!Invocation.getMigratorOptions().shouldRunMigrator())
     return false;

   // Delete the remap file, in case someone is re-running the Migrator. If the
   // file fails to compile and we don't get a chance to overwrite it, the old
   // changes may get picked up.
   llvm::sys::fs::remove(Invocation.getMigratorOptions().EmitRemapFilePath);

   Migrator M { Instance, Invocation }; // Provide inputs and configuration
   auto EffectiveVersion = Invocation.getLangOptions().EffectiveLanguageVersion;
   auto CurrentVersion = version::Version::getCurrentLanguageVersion();

   // Phase 1: Pre Fix-it passes
   // These uses the initial frontend invocation to apply any obvious fix-its
   // to see if we can get an error-free AST to get to Phase 2.
   std::unique_ptr<swift::CompilerInstance> PreFixItInstance;
   if (Instance->getASTContext().hadError()) {
     PreFixItInstance = M.repeatFixitMigrations(2, EffectiveVersion);

     // If we still couldn't fix all of the errors, give up.
     if (PreFixItInstance == nullptr ||
         !PreFixItInstance->hasASTContext() ||
         PreFixItInstance->getASTContext().hadError()) {
       return true;
     }
     M.StartInstance = PreFixItInstance.get();
   }

   // Phase 2: Syntactic Transformations
   // Don't run these passes if we're already in newest Swift version.
   if (EffectiveVersion != CurrentVersion) {
     SyntacticPassOptions Opts;

     // Type of optional try changes since Swift 5.
     Opts.RunOptionalTryMigration = !EffectiveVersion.isVersionAtLeast(5);
     auto FailedSyntacticPasses = M.performSyntacticPasses(Opts);
     if (FailedSyntacticPasses) {
       return true;
     }
   }

   // Phase 3: Post Fix-it Passes
   // Perform fix-it based migrations on the compiler, some number of times in
   // order to give the compiler an opportunity to
   // take its time reaching a fixed point.
   // This is the end of the pipeline, so we throw away the compiler instance(s)
   // we used in these fix-it runs.

   if (M.getMigratorOptions().EnableMigratorFixits) {
     M.repeatFixitMigrations(Migrator::MaxCompilerFixitPassIterations,
                             CurrentVersion);
   }

   // OK, we have a final resulting text. Now we compare against the input
   // to calculate a replacement map describing the changes to the input
   // necessary to get the output.
   // TODO: Document replacement map format.


   auto EmitRemapFailed = M.emitRemap();
   auto EmitMigratedFailed = M.emitMigratedFile();
   auto DumpMigrationStatesFailed = M.dumpStates();
   return EmitRemapFailed || EmitMigratedFailed || DumpMigrationStatesFailed;
 }

 Migrator::Migrator(CompilerInstance *StartInstance,
                    const CompilerInvocation &StartInvocation)
   : StartInstance(StartInstance), StartInvocation(StartInvocation) {

     auto ErrorOrStartBuffer = llvm::MemoryBuffer::getFile(getInputFilename());
     auto &StartBuffer = ErrorOrStartBuffer.get();
     auto StartBufferID = SrcMgr.addNewSourceBuffer(std::move(StartBuffer));
     States.push_back(MigrationState::start(SrcMgr, StartBufferID));
 }

 std::unique_ptr<swift::CompilerInstance>
 Migrator::repeatFixitMigrations(const unsigned Iterations,
                                 version::Version SwiftLanguageVersion) {
   for (unsigned i = 0; i < Iterations; ++i) {
     auto ThisInstance = performAFixItMigration(SwiftLanguageVersion);
     if (ThisInstance == nullptr) {
       break;
     } else {
       if (States.back()->noChangesOccurred()) {
         return ThisInstance;
       }
     }
   }
   return nullptr;
 }

 std::unique_ptr<swift::CompilerInstance>
 Migrator::performAFixItMigration(version::Version SwiftLanguageVersion) {
   auto InputState = States.back();
   auto InputText = InputState->getOutputText();
   auto InputBuffer =
     llvm::MemoryBuffer::getMemBufferCopy(InputText, getInputFilename());

   CompilerInvocation Invocation { StartInvocation };
   Invocation.getFrontendOptions().InputsAndOutputs.clearInputs();
   Invocation.getLangOptions().EffectiveLanguageVersion = SwiftLanguageVersion;
   auto &LLVMArgs = Invocation.getFrontendOptions().LLVMArgs;
   auto aarch64_use_tbi = std::find(LLVMArgs.begin(), LLVMArgs.end(),
                                    "-aarch64-use-tbi");
   if (aarch64_use_tbi != LLVMArgs.end()) {
     LLVMArgs.erase(aarch64_use_tbi);
   }

   const auto &OrigFrontendOpts = StartInvocation.getFrontendOptions();

   assert(OrigFrontendOpts.InputsAndOutputs.hasPrimaryInputs() &&
          "Migration must have a primary");
   for (const auto &input : OrigFrontendOpts.InputsAndOutputs.getAllInputs()) {
     Invocation.getFrontendOptions().InputsAndOutputs.addInput(
         InputFile(input.file(), input.isPrimary(),
                   input.isPrimary() ? InputBuffer.get() : input.buffer()));
   }

   auto Instance = llvm::make_unique<swift::CompilerInstance>();
   if (Instance->setup(Invocation)) {
     return nullptr;
   }

   FixitApplyDiagnosticConsumer FixitApplyConsumer {
     InputText,
     getInputFilename(),
   };
   Instance->addDiagnosticConsumer(&FixitApplyConsumer);

   Instance->performSema();

   StringRef ResultText = InputText;
   unsigned ResultBufferID = InputState->getOutputBufferID();

   if (FixitApplyConsumer.getNumFixitsApplied() > 0) {
     SmallString<4096> Scratch;
     llvm::raw_svector_ostream OS(Scratch);
     FixitApplyConsumer.printResult(OS);
     auto ResultBuffer = llvm::MemoryBuffer::getMemBufferCopy(OS.str());
     ResultText = ResultBuffer->getBuffer();
     ResultBufferID = SrcMgr.addNewSourceBuffer(std::move(ResultBuffer));
   }

   States.push_back(MigrationState::make(MigrationKind::CompilerFixits,
                                         SrcMgr, InputState->getOutputBufferID(),
                                         ResultBufferID));
   return Instance;
 }

 bool Migrator::performSyntacticPasses(SyntacticPassOptions Opts) {
   clang::FileSystemOptions ClangFileSystemOptions;
   clang::FileManager ClangFileManager { ClangFileSystemOptions };

   llvm::IntrusiveRefCntPtr<clang::DiagnosticIDs> DummyClangDiagIDs {
     new clang::DiagnosticIDs()
   };
   auto ClangDiags =
     llvm::make_unique<clang::DiagnosticsEngine>(DummyClangDiagIDs,
                                                 new clang::DiagnosticOptions,
                                                 new clang::DiagnosticConsumer(),
                                                 /*ShouldOwnClient=*/true);

   clang::SourceManager ClangSourceManager { *ClangDiags, ClangFileManager };
   clang::LangOptions ClangLangOpts;
   clang::edit::EditedSource Edits { ClangSourceManager, ClangLangOpts };

   auto InputState = States.back();
   auto InputText = InputState->getOutputText();

   EditorAdapter Editor { StartInstance->getSourceMgr(), ClangSourceManager };

   runAPIDiffMigratorPass(Editor, StartInstance->getPrimarySourceFile(),
                          getMigratorOptions());
   if (Opts.RunOptionalTryMigration) {
     runOptionalTryMigratorPass(Editor, StartInstance->getPrimarySourceFile(),
                                getMigratorOptions());
   }

   Edits.commit(Editor.getEdits());

   RewriteBufferEditsReceiver Rewriter {
     ClangSourceManager,
     Editor.getClangFileIDForSwiftBufferID(
       StartInstance->getPrimarySourceFile()->getBufferID().getValue()),
     InputState->getOutputText()
   };

   Edits.applyRewrites(Rewriter);

   SmallString<1024> Scratch;
   llvm::raw_svector_ostream OS(Scratch);
   Rewriter.printResult(OS);
   auto ResultBuffer = this->SrcMgr.addMemBufferCopy(OS.str());

   States.push_back(
     MigrationState::make(MigrationKind::Syntactic,
                          this->SrcMgr,
                          States.back()->getInputBufferID(),
                          ResultBuffer));
   return false;
 }

 namespace {
 /// Print a replacement from a diff edit scriptto the given output stream.
 ///
 /// \param Filename The filename of the original file
 /// \param Rep The Replacement to print
 /// \param OS The output stream
 void printReplacement(const StringRef Filename,
                       const Replacement &Rep,
                       llvm::raw_ostream &OS) {
   assert(!Filename.empty());
   if (Rep.Remove == 0 && Rep.Text.empty()) {
     return;
   }
   OS << "  {\n";

   OS << "    \"file\": \"";
   OS.write_escaped(Filename);
   OS << "\",\n";

   OS << "    \"offset\": " << Rep.Offset;
   if (Rep.Remove > 0) {
     OS << ",\n";
     OS << "    \"remove\": " << Rep.Remove;
   }
   if (!Rep.Text.empty()) {
     OS << ",\n";
     OS << "    \"text\": \"";
     OS.write_escaped(Rep.Text);
     OS << "\"\n";
   } else {
     OS << "\n";
   }
   OS << "  }";
 }

 /// Print a remap file to the given output stream.
 ///
 /// \param OriginalFilename The filename of the file that was edited
 /// not the output file for printing here.
 /// \param InputText The input text without any changes.
 /// \param OutputText The result text after any changes.
 /// \param OS The output stream.
 void printRemap(const StringRef OriginalFilename,
                 const StringRef InputText,
                 const StringRef OutputText,
                 llvm::raw_ostream &OS) {
   assert(!OriginalFilename.empty());

   diff_match_patch<std::string> DMP;
   const auto Diffs = DMP.diff_main(InputText, OutputText, /*checkLines=*/false);

   OS << "[";

   size_t Offset = 0;

   llvm::SmallVector<Replacement, 32> Replacements;

   for (const auto &Diff : Diffs) {
     size_t OffsetIncrement = 0;
     switch (Diff.operation) {
       case decltype(DMP)::EQUAL:
         OffsetIncrement += Diff.text.size();
         break;
       case decltype(DMP)::INSERT:
         Replacements.push_back({ Offset, 0, Diff.text });
         break;
       case decltype(DMP)::DELETE:
         Replacements.push_back({ Offset, Diff.text.size(), "" });
         OffsetIncrement = Diff.text.size();
         break;
     }
     Offset += OffsetIncrement;
   }

   assert(Offset == InputText.size());

   // Combine removal edits with previous edits that are consecutive.
   for (unsigned i = 1; i < Replacements.size();) {
     auto &Previous = Replacements[i-1];
     auto &Current = Replacements[i];
     assert(Current.Offset >= Previous.Offset + Previous.Remove);
     unsigned Distance = Current.Offset-(Previous.Offset + Previous.Remove);
     if (Distance > 0) {
       ++i;
       continue;
     }
     if (!Current.Text.empty()) {
       ++i;
       continue;
     }
     Previous.Remove += Current.Remove;
     Replacements.erase(Replacements.begin() + i);
   }

   // Combine removal edits with next edits that are consecutive.
   for (unsigned i = 0; i + 1 < Replacements.size();) {
     auto &Current = Replacements[i];
     auto &nextRep = Replacements[i + 1];
     assert(nextRep.Offset >= Current.Offset + Current.Remove);
     unsigned Distance = nextRep.Offset - (Current.Offset + Current.Remove);
     if (Distance > 0) {
       ++i;
       continue;
     }
     if (!Current.Text.empty()) {
       ++i;
       continue;
     }
     nextRep.Offset -= Current.Remove;
     nextRep.Remove += Current.Remove;
     Replacements.erase(Replacements.begin() + i);
   }

   // For remaining removal diffs, include the byte adjacent to the range on the
   // left. libclang applies the diffs as byte diffs, so it doesn't matter if the
   // byte is part of a multi-byte UTF8 character.
   for (unsigned i = 0; i < Replacements.size(); ++i) {
     auto &Current = Replacements[i];
     if (!Current.Text.empty())
       continue;
     if (Current.Offset == 0)
       continue;
     Current.Offset -= 1;
     Current.Remove += 1;
     Current.Text = InputText.substr(Current.Offset, 1);
   }

   for (auto Rep = Replacements.begin(); Rep != Replacements.end(); ++Rep) {
     if (Rep != Replacements.begin()) {
       OS << ",\n";
     } else {
       OS << "\n";
     }
     printReplacement(OriginalFilename, *Rep, OS);
   }

   OS << "\n]";
 }

 } // end anonymous namespace

 bool Migrator::emitRemap() const {
   const auto &RemapPath = getMigratorOptions().EmitRemapFilePath;
   if (RemapPath.empty()) {
     return false;
   }

   std::error_code Error;
   llvm::raw_fd_ostream FileOS(RemapPath,
                               Error, llvm::sys::fs::F_Text);
   if (FileOS.has_error()) {
     return true;
   }

   auto InputText = States.front()->getOutputText();
   auto OutputText = States.back()->getOutputText();
   printRemap(getInputFilename(), InputText, OutputText, FileOS);

   FileOS.flush();
   return FileOS.has_error();
 }

 bool Migrator::emitMigratedFile() const {
   const auto &OutFilename = getMigratorOptions().EmitMigratedFilePath;
   if (OutFilename.empty()) {
     return false;
   }

   std::error_code Error;
   llvm::raw_fd_ostream FileOS(OutFilename,
                               Error, llvm::sys::fs::F_Text);
   if (FileOS.has_error()) {
     return true;
   }

   FileOS << States.back()->getOutputText();

   FileOS.flush();

   return FileOS.has_error();
 }

 bool Migrator::dumpStates() const {
   const auto &OutDir = getMigratorOptions().DumpMigrationStatesDir;
   if (OutDir.empty()) {
     return false;
   }

   auto Failed = false;
   for (size_t i = 0; i < States.size(); ++i) {
     Failed |= States[i]->print(i, OutDir);
   }

   return Failed;
 }

 const MigratorOptions &Migrator::getMigratorOptions() const {
   return StartInvocation.getMigratorOptions();
 }

 const StringRef Migrator::getInputFilename() const {
   auto &PrimaryInput = StartInvocation.getFrontendOptions()
                            .InputsAndOutputs.getRequiredUniquePrimaryInput();
   return PrimaryInput.file();
 }
	//===--- Migrator.cpp -----------------------------------------------------===//
	// This source file is part of the Swift.org open source project
	//
	// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
	// Licensed under Apache License v2.0 with Runtime Library Exception
	//
	// See https://swift.org/LICENSE.txt for license information
	// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
	//
	//===----------------------------------------------------------------------===//

	#include "swift/Basic/Diff.h"
	#include "swift/Frontend/Frontend.h"
	#include "swift/Migrator/ASTMigratorPass.h"
	#include "swift/Migrator/EditorAdapter.h"
	#include "swift/Migrator/FixitApplyDiagnosticConsumer.h"
	#include "swift/Migrator/Migrator.h"
	#include "swift/Migrator/RewriteBufferEditsReceiver.h"
	#include "clang/Basic/Diagnostic.h"
	#include "clang/Basic/FileManager.h"
	#include "clang/Basic/SourceManager.h"
	#include "clang/Edit/EditedSource.h"
	#include "clang/Rewrite/Core/RewriteBuffer.h"
	#include "llvm/Support/FileSystem.h"

	using namespace swift;
	using namespace swift::migrator;

	bool migrator::updateCodeAndEmitRemapIfNeeded(
	CompilerInstance *Instance, const CompilerInvocation &Invocation) {
	if (!Invocation.getMigratorOptions().shouldRunMigrator())
	return false;

	// Delete the remap file, in case someone is re-running the Migrator. If the
	// file fails to compile and we don't get a chance to overwrite it, the old
	// changes may get picked up.
	llvm::sys::fs::remove(Invocation.getMigratorOptions().EmitRemapFilePath);

	Migrator M { Instance, Invocation }; // Provide inputs and configuration
	auto EffectiveVersion = Invocation.getLangOptions().EffectiveLanguageVersion;
	auto CurrentVersion = version::Version::getCurrentLanguageVersion();

	// Phase 1: Pre Fix-it passes
	// These uses the initial frontend invocation to apply any obvious fix-its
	// to see if we can get an error-free AST to get to Phase 2.
	std::unique_ptr<swift::CompilerInstance> PreFixItInstance;
	if (Instance->getASTContext().hadError()) {
	PreFixItInstance = M.repeatFixitMigrations(2, EffectiveVersion);

	// If we still couldn't fix all of the errors, give up.
	if (PreFixItInstance == nullptr \|\|
	!PreFixItInstance->hasASTContext() \|\|
	PreFixItInstance->getASTContext().hadError()) {
	return true;
	}
	M.StartInstance = PreFixItInstance.get();
	}

	// Phase 2: Syntactic Transformations
	// Don't run these passes if we're already in newest Swift version.
	if (EffectiveVersion != CurrentVersion) {
	SyntacticPassOptions Opts;

	// Type of optional try changes since Swift 5.
	Opts.RunOptionalTryMigration = !EffectiveVersion.isVersionAtLeast(5);
	auto FailedSyntacticPasses = M.performSyntacticPasses(Opts);
	if (FailedSyntacticPasses) {
	return true;
	}
	}

	// Phase 3: Post Fix-it Passes
	// Perform fix-it based migrations on the compiler, some number of times in
	// order to give the compiler an opportunity to
	// take its time reaching a fixed point.
	// This is the end of the pipeline, so we throw away the compiler instance(s)
	// we used in these fix-it runs.

	if (M.getMigratorOptions().EnableMigratorFixits) {
	M.repeatFixitMigrations(Migrator::MaxCompilerFixitPassIterations,
	CurrentVersion);
	}

	// OK, we have a final resulting text. Now we compare against the input
	// to calculate a replacement map describing the changes to the input
	// necessary to get the output.
	// TODO: Document replacement map format.


	auto EmitRemapFailed = M.emitRemap();
	auto EmitMigratedFailed = M.emitMigratedFile();
	auto DumpMigrationStatesFailed = M.dumpStates();
	return EmitRemapFailed \|\| EmitMigratedFailed \|\| DumpMigrationStatesFailed;
	}

	Migrator::Migrator(CompilerInstance *StartInstance,
	const CompilerInvocation &StartInvocation)
	: StartInstance(StartInstance), StartInvocation(StartInvocation) {

	auto ErrorOrStartBuffer = llvm::MemoryBuffer::getFile(getInputFilename());
	auto &StartBuffer = ErrorOrStartBuffer.get();
	auto StartBufferID = SrcMgr.addNewSourceBuffer(std::move(StartBuffer));
	States.push_back(MigrationState::start(SrcMgr, StartBufferID));
	}

	std::unique_ptr<swift::CompilerInstance>
	Migrator::repeatFixitMigrations(const unsigned Iterations,
	version::Version SwiftLanguageVersion) {
	for (unsigned i = 0; i < Iterations; ++i) {
	auto ThisInstance = performAFixItMigration(SwiftLanguageVersion);
	if (ThisInstance == nullptr) {
	break;
	} else {
	if (States.back()->noChangesOccurred()) {
	return ThisInstance;
	}
	}
	}
	return nullptr;
	}

	std::unique_ptr<swift::CompilerInstance>
	Migrator::performAFixItMigration(version::Version SwiftLanguageVersion) {
	auto InputState = States.back();
	auto InputText = InputState->getOutputText();
	auto InputBuffer =
	llvm::MemoryBuffer::getMemBufferCopy(InputText, getInputFilename());

	CompilerInvocation Invocation { StartInvocation };
	Invocation.getFrontendOptions().InputsAndOutputs.clearInputs();
	Invocation.getLangOptions().EffectiveLanguageVersion = SwiftLanguageVersion;
	auto &LLVMArgs = Invocation.getFrontendOptions().LLVMArgs;
	auto aarch64_use_tbi = std::find(LLVMArgs.begin(), LLVMArgs.end(),
	"-aarch64-use-tbi");
	if (aarch64_use_tbi != LLVMArgs.end()) {
	LLVMArgs.erase(aarch64_use_tbi);
	}

	const auto &OrigFrontendOpts = StartInvocation.getFrontendOptions();

	assert(OrigFrontendOpts.InputsAndOutputs.hasPrimaryInputs() &&
	"Migration must have a primary");
	for (const auto &input : OrigFrontendOpts.InputsAndOutputs.getAllInputs()) {
	Invocation.getFrontendOptions().InputsAndOutputs.addInput(
	InputFile(input.file(), input.isPrimary(),
	input.isPrimary() ? InputBuffer.get() : input.buffer()));
	}

	auto Instance = llvm::make_unique<swift::CompilerInstance>();
	if (Instance->setup(Invocation)) {
	return nullptr;
	}

	FixitApplyDiagnosticConsumer FixitApplyConsumer {
	InputText,
	getInputFilename(),
	};
	Instance->addDiagnosticConsumer(&FixitApplyConsumer);

	Instance->performSema();

	StringRef ResultText = InputText;
	unsigned ResultBufferID = InputState->getOutputBufferID();

	if (FixitApplyConsumer.getNumFixitsApplied() > 0) {
	SmallString<4096> Scratch;
	llvm::raw_svector_ostream OS(Scratch);
	FixitApplyConsumer.printResult(OS);
	auto ResultBuffer = llvm::MemoryBuffer::getMemBufferCopy(OS.str());
	ResultText = ResultBuffer->getBuffer();
	ResultBufferID = SrcMgr.addNewSourceBuffer(std::move(ResultBuffer));
	}

	States.push_back(MigrationState::make(MigrationKind::CompilerFixits,
	SrcMgr, InputState->getOutputBufferID(),
	ResultBufferID));
	return Instance;
	}

	bool Migrator::performSyntacticPasses(SyntacticPassOptions Opts) {
	clang::FileSystemOptions ClangFileSystemOptions;
	clang::FileManager ClangFileManager { ClangFileSystemOptions };

	llvm::IntrusiveRefCntPtr<clang::DiagnosticIDs> DummyClangDiagIDs {
	new clang::DiagnosticIDs()
	};
	auto ClangDiags =
	llvm::make_unique<clang::DiagnosticsEngine>(DummyClangDiagIDs,
	new clang::DiagnosticOptions,
	new clang::DiagnosticConsumer(),
	/ShouldOwnClient=/true);

	clang::SourceManager ClangSourceManager { *ClangDiags, ClangFileManager };
	clang::LangOptions ClangLangOpts;
	clang::edit::EditedSource Edits { ClangSourceManager, ClangLangOpts };

	auto InputState = States.back();
	auto InputText = InputState->getOutputText();

	EditorAdapter Editor { StartInstance->getSourceMgr(), ClangSourceManager };

	runAPIDiffMigratorPass(Editor, StartInstance->getPrimarySourceFile(),
	getMigratorOptions());
	if (Opts.RunOptionalTryMigration) {
	runOptionalTryMigratorPass(Editor, StartInstance->getPrimarySourceFile(),
	getMigratorOptions());
	}

	Edits.commit(Editor.getEdits());

	RewriteBufferEditsReceiver Rewriter {
	ClangSourceManager,
	Editor.getClangFileIDForSwiftBufferID(
	StartInstance->getPrimarySourceFile()->getBufferID().getValue()),
	InputState->getOutputText()
	};

	Edits.applyRewrites(Rewriter);

	SmallString<1024> Scratch;
	llvm::raw_svector_ostream OS(Scratch);
	Rewriter.printResult(OS);
	auto ResultBuffer = this->SrcMgr.addMemBufferCopy(OS.str());

	States.push_back(
	MigrationState::make(MigrationKind::Syntactic,
	this->SrcMgr,
	States.back()->getInputBufferID(),
	ResultBuffer));
	return false;
	}

	namespace {
	/// Print a replacement from a diff edit scriptto the given output stream.
	///
	/// \param Filename The filename of the original file
	/// \param Rep The Replacement to print
	/// \param OS The output stream
	void printReplacement(const StringRef Filename,
	const Replacement &Rep,
	llvm::raw_ostream &OS) {
	assert(!Filename.empty());
	if (Rep.Remove == 0 && Rep.Text.empty()) {
	return;
	}
	OS << " {\n";

	OS << " \"file\": \"";
	OS.write_escaped(Filename);
	OS << "\",\n";

	OS << " \"offset\": " << Rep.Offset;
	if (Rep.Remove > 0) {
	OS << ",\n";
	OS << " \"remove\": " << Rep.Remove;
	}
	if (!Rep.Text.empty()) {
	OS << ",\n";
	OS << " \"text\": \"";
	OS.write_escaped(Rep.Text);
	OS << "\"\n";
	} else {
	OS << "\n";
	}
	OS << " }";
	}

	/// Print a remap file to the given output stream.
	///
	/// \param OriginalFilename The filename of the file that was edited
	/// not the output file for printing here.
	/// \param InputText The input text without any changes.
	/// \param OutputText The result text after any changes.
	/// \param OS The output stream.
	void printRemap(const StringRef OriginalFilename,
	const StringRef InputText,
	const StringRef OutputText,
	llvm::raw_ostream &OS) {
	assert(!OriginalFilename.empty());

	diff_match_patch<std::string> DMP;
	const auto Diffs = DMP.diff_main(InputText, OutputText, /checkLines=/false);

	OS << "[";

	size_t Offset = 0;

	llvm::SmallVector<Replacement, 32> Replacements;

	for (const auto &Diff : Diffs) {
	size_t OffsetIncrement = 0;
	switch (Diff.operation) {
	case decltype(DMP)::EQUAL:
	OffsetIncrement += Diff.text.size();
	break;
	case decltype(DMP)::INSERT:
	Replacements.push_back({ Offset, 0, Diff.text });
	break;
	case decltype(DMP)::DELETE:
	Replacements.push_back({ Offset, Diff.text.size(), "" });
	OffsetIncrement = Diff.text.size();
	break;
	}
	Offset += OffsetIncrement;
	}

	assert(Offset == InputText.size());

	// Combine removal edits with previous edits that are consecutive.
	for (unsigned i = 1; i < Replacements.size();) {
	auto &Previous = Replacements[i-1];
	auto &Current = Replacements[i];
	assert(Current.Offset >= Previous.Offset + Previous.Remove);
	unsigned Distance = Current.Offset-(Previous.Offset + Previous.Remove);
	if (Distance > 0) {
	++i;
	continue;
	}
	if (!Current.Text.empty()) {
	++i;
	continue;
	}
	Previous.Remove += Current.Remove;
	Replacements.erase(Replacements.begin() + i);
	}

	// Combine removal edits with next edits that are consecutive.
	for (unsigned i = 0; i + 1 < Replacements.size();) {
	auto &Current = Replacements[i];
	auto &nextRep = Replacements[i + 1];
	assert(nextRep.Offset >= Current.Offset + Current.Remove);
	unsigned Distance = nextRep.Offset - (Current.Offset + Current.Remove);
	if (Distance > 0) {
	++i;
	continue;
	}
	if (!Current.Text.empty()) {
	++i;
	continue;
	}
	nextRep.Offset -= Current.Remove;
	nextRep.Remove += Current.Remove;
	Replacements.erase(Replacements.begin() + i);
	}

	// For remaining removal diffs, include the byte adjacent to the range on the
	// left. libclang applies the diffs as byte diffs, so it doesn't matter if the
	// byte is part of a multi-byte UTF8 character.
	for (unsigned i = 0; i < Replacements.size(); ++i) {
	auto &Current = Replacements[i];
	if (!Current.Text.empty())
	continue;
	if (Current.Offset == 0)
	continue;
	Current.Offset -= 1;
	Current.Remove += 1;
	Current.Text = InputText.substr(Current.Offset, 1);
	}

	for (auto Rep = Replacements.begin(); Rep != Replacements.end(); ++Rep) {
	if (Rep != Replacements.begin()) {
	OS << ",\n";
	} else {
	OS << "\n";
	}
	printReplacement(OriginalFilename, *Rep, OS);
	}

	OS << "\n]";
	}

	} // end anonymous namespace

	bool Migrator::emitRemap() const {
	const auto &RemapPath = getMigratorOptions().EmitRemapFilePath;
	if (RemapPath.empty()) {
	return false;
	}

	std::error_code Error;
	llvm::raw_fd_ostream FileOS(RemapPath,
	Error, llvm::sys::fs::F_Text);
	if (FileOS.has_error()) {
	return true;
	}

	auto InputText = States.front()->getOutputText();
	auto OutputText = States.back()->getOutputText();
	printRemap(getInputFilename(), InputText, OutputText, FileOS);

	FileOS.flush();
	return FileOS.has_error();
	}

	bool Migrator::emitMigratedFile() const {
	const auto &OutFilename = getMigratorOptions().EmitMigratedFilePath;
	if (OutFilename.empty()) {
	return false;
	}

	std::error_code Error;
	llvm::raw_fd_ostream FileOS(OutFilename,
	Error, llvm::sys::fs::F_Text);
	if (FileOS.has_error()) {
	return true;
	}

	FileOS << States.back()->getOutputText();

	FileOS.flush();

	return FileOS.has_error();
	}

	bool Migrator::dumpStates() const {
	const auto &OutDir = getMigratorOptions().DumpMigrationStatesDir;
	if (OutDir.empty()) {
	return false;
	}

	auto Failed = false;
	for (size_t i = 0; i < States.size(); ++i) {
	Failed \|= States[i]->print(i, OutDir);
	}

	return Failed;
	}

	const MigratorOptions &Migrator::getMigratorOptions() const {
	return StartInvocation.getMigratorOptions();
	}

	const StringRef Migrator::getInputFilename() const {
	auto &PrimaryInput = StartInvocation.getFrontendOptions()
	.InputsAndOutputs.getRequiredUniquePrimaryInput();
	return PrimaryInput.file();
	}