tools/gn/ninja_c_binary_target_writer.cc

// Copyright 2019 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.

#include "tools/gn/ninja_c_binary_target_writer.h"

#include <stddef.h>
#include <string.h>

#include <cstring>
#include <set>
#include <sstream>
#include <unordered_set>

#include "base/strings/string_util.h"
#include "tools/gn/c_substitution_type.h"
#include "tools/gn/config_values_extractors.h"
#include "tools/gn/deps_iterator.h"
#include "tools/gn/err.h"
#include "tools/gn/escape.h"
#include "tools/gn/filesystem_utils.h"
#include "tools/gn/general_tool.h"
#include "tools/gn/ninja_target_command_util.h"
#include "tools/gn/ninja_utils.h"
#include "tools/gn/scheduler.h"
#include "tools/gn/settings.h"
#include "tools/gn/string_utils.h"
#include "tools/gn/substitution_writer.h"
#include "tools/gn/target.h"

namespace {

// Returns the proper escape options for writing compiler and linker flags.
EscapeOptions GetFlagOptions() {
  EscapeOptions opts;
  opts.mode = ESCAPE_NINJA_COMMAND;
  return opts;
}

// Returns the language-specific lang recognized by gcc’s -x flag for
// precompiled header files.
const char* GetPCHLangForToolType(const char* name) {
  if (name == CTool::kCToolCc)
    return "c-header";
  if (name == CTool::kCToolCxx)
    return "c++-header";
  if (name == CTool::kCToolObjC)
    return "objective-c-header";
  if (name == CTool::kCToolObjCxx)
    return "objective-c++-header";
  NOTREACHED() << "Not a valid PCH tool type: " << name;
  return "";
}

// Appends the object files generated by the given source set to the given
// output vector.
void AddSourceSetObjectFiles(const Target* source_set,
                             UniqueVector<OutputFile>* obj_files) {
  std::vector<OutputFile> tool_outputs;  // Prevent allocation in loop.
  NinjaBinaryTargetWriter::SourceFileTypeSet used_types;

  // Compute object files for all sources. Only link the first output from
  // the tool if there are more than one.
  for (const auto& source : source_set->sources()) {
    const char* tool_name = Tool::kToolNone;
    if (source_set->GetOutputFilesForSource(source, &tool_name, &tool_outputs))
      obj_files->push_back(tool_outputs[0]);

    used_types.Set(source.type());
  }

  // Add MSVC precompiled header object files. GCC .gch files are not object
  // files so they are omitted.
  if (source_set->config_values().has_precompiled_headers()) {
    if (used_types.Get(SourceFile::SOURCE_C)) {
      const CTool* tool = source_set->toolchain()->GetToolAsC(CTool::kCToolCc);
      if (tool && tool->precompiled_header_type() == CTool::PCH_MSVC) {
        GetPCHOutputFiles(source_set, CTool::kCToolCc, &tool_outputs);
        obj_files->Append(tool_outputs.begin(), tool_outputs.end());
      }
    }
    if (used_types.Get(SourceFile::SOURCE_CPP)) {
      const CTool* tool = source_set->toolchain()->GetToolAsC(CTool::kCToolCxx);
      if (tool && tool->precompiled_header_type() == CTool::PCH_MSVC) {
        GetPCHOutputFiles(source_set, CTool::kCToolCxx, &tool_outputs);
        obj_files->Append(tool_outputs.begin(), tool_outputs.end());
      }
    }
    if (used_types.Get(SourceFile::SOURCE_M)) {
      const CTool* tool =
          source_set->toolchain()->GetToolAsC(CTool::kCToolObjC);
      if (tool && tool->precompiled_header_type() == CTool::PCH_MSVC) {
        GetPCHOutputFiles(source_set, CTool::kCToolObjC, &tool_outputs);
        obj_files->Append(tool_outputs.begin(), tool_outputs.end());
      }
    }
    if (used_types.Get(SourceFile::SOURCE_MM)) {
      const CTool* tool =
          source_set->toolchain()->GetToolAsC(CTool::kCToolObjCxx);
      if (tool && tool->precompiled_header_type() == CTool::PCH_MSVC) {
        GetPCHOutputFiles(source_set, CTool::kCToolObjCxx, &tool_outputs);
        obj_files->Append(tool_outputs.begin(), tool_outputs.end());
      }
    }
  }
}

}  // namespace

NinjaCBinaryTargetWriter::NinjaCBinaryTargetWriter(const Target* target,
                                                   std::ostream& out)
    : NinjaBinaryTargetWriter(target, out),
      tool_(target->toolchain()->GetToolForTargetFinalOutputAsC(target)) {}

NinjaCBinaryTargetWriter::~NinjaCBinaryTargetWriter() = default;

void NinjaCBinaryTargetWriter::Run() {
  // Figure out what source types are needed.
  SourceFileTypeSet used_types;
  for (const auto& source : target_->sources())
    used_types.Set(source.type());

  WriteCompilerVars(used_types);

  OutputFile input_dep = WriteInputsStampAndGetDep();

  // The input dependencies will be an order-only dependency. This will cause
  // Ninja to make sure the inputs are up to date before compiling this source,
  // but changes in the inputs deps won't cause the file to be recompiled.
  //
  // This is important to prevent changes in unrelated actions that are
  // upstream of this target from causing everything to be recompiled.
  //
  // Why can we get away with this rather than using implicit deps ("|", which
  // will force rebuilds when the inputs change)? For source code, the
  // computed dependencies of all headers will be computed by the compiler,
  // which will cause source rebuilds if any "real" upstream dependencies
  // change.
  //
  // If a .cc file is generated by an input dependency, Ninja will see the
  // input to the build rule doesn't exist, and that it is an output from a
  // previous step, and build the previous step first. This is a "real"
  // dependency and doesn't need | or || to express.
  //
  // The only case where this rule matters is for the first build where no .d
  // files exist, and Ninja doesn't know what that source file depends on. In
  // this case it's sufficient to ensure that the upstream dependencies are
  // built first. This is exactly what Ninja's order-only dependencies
  // expresses.
  //
  // The order only deps are referenced by each source file compile,
  // but also by PCH compiles.  The latter are annoying to count, so omit
  // them here.  This means that binary targets with a single source file
  // that also use PCH files won't have a stamp file even though having
  // one would make output ninja file size a bit lower. That's ok, binary
  // targets with a single source are rare.
  size_t num_stamp_uses = target_->sources().size();
  std::vector<OutputFile> order_only_deps = WriteInputDepsStampAndGetDep(
      std::vector<const Target*>(), num_stamp_uses);

  // For GCC builds, the .gch files are not object files, but still need to be
  // added as explicit dependencies below. The .gch output files are placed in
  // |pch_other_files|. This is to prevent linking against them.
  std::vector<OutputFile> pch_obj_files;
  std::vector<OutputFile> pch_other_files;
  WritePCHCommands(used_types, input_dep, order_only_deps, &pch_obj_files,
                   &pch_other_files);
  std::vector<OutputFile>* pch_files =
      !pch_obj_files.empty() ? &pch_obj_files : &pch_other_files;

  // Treat all pch output files as explicit dependencies of all
  // compiles that support them. Some notes:
  //
  //  - On Windows, the .pch file is the input to the compile, not the
  //    precompiled header's corresponding object file that we're using here.
  //    But Ninja's depslog doesn't support multiple outputs from the
  //    precompiled header compile step (it outputs both the .pch file and a
  //    corresponding .obj file). So we consistently list the .obj file and the
  //    .pch file we really need comes along with it.
  //
  //  - GCC .gch files are not object files, therefore they are not added to the
  //    object file list.
  std::vector<OutputFile> obj_files;
  std::vector<SourceFile> other_files;
  WriteSources(*pch_files, input_dep, order_only_deps, &obj_files,
               &other_files);

  // Link all MSVC pch object files. The vector will be empty on GCC toolchains.
  obj_files.insert(obj_files.end(), pch_obj_files.begin(), pch_obj_files.end());
  if (!CheckForDuplicateObjectFiles(obj_files))
    return;

  if (target_->output_type() == Target::SOURCE_SET) {
    WriteSourceSetStamp(obj_files);
#ifndef NDEBUG
    // Verify that the function that separately computes a source set's object
    // files match the object files just computed.
    UniqueVector<OutputFile> computed_obj;
    AddSourceSetObjectFiles(target_, &computed_obj);
    DCHECK_EQ(obj_files.size(), computed_obj.size());
    for (const auto& obj : obj_files)
      DCHECK_NE(static_cast<size_t>(-1), computed_obj.IndexOf(obj));
#endif
  } else {
    WriteLinkerStuff(obj_files, other_files, input_dep);
  }
}

void NinjaCBinaryTargetWriter::WriteCompilerVars(
    const SourceFileTypeSet& used_types) {
  const SubstitutionBits& subst = target_->toolchain()->substitution_bits();

  // Defines.
  if (subst.used.count(&CSubstitutionDefines)) {
    out_ << CSubstitutionDefines.ninja_name << " =";
    RecursiveTargetConfigToStream<std::string>(target_, &ConfigValues::defines,
                                               DefineWriter(), out_);
    out_ << std::endl;
  }

  // Include directories.
  if (subst.used.count(&CSubstitutionIncludeDirs)) {
    out_ << CSubstitutionIncludeDirs.ninja_name << " =";
    PathOutput include_path_output(
        path_output_.current_dir(),
        settings_->build_settings()->root_path_utf8(), ESCAPE_NINJA_COMMAND);
    RecursiveTargetConfigToStream<SourceDir>(
        target_, &ConfigValues::include_dirs,
        IncludeWriter(include_path_output), out_);
    out_ << std::endl;
  }

  bool has_precompiled_headers =
      target_->config_values().has_precompiled_headers();

  EscapeOptions opts = GetFlagOptions();
  if (used_types.Get(SourceFile::SOURCE_S) ||
      used_types.Get(SourceFile::SOURCE_ASM)) {
    WriteOneFlag(target_, &CSubstitutionAsmFlags, false, Tool::kToolNone,
                 &ConfigValues::asmflags, opts, path_output_, out_);
  }
  if (used_types.Get(SourceFile::SOURCE_C) ||
      used_types.Get(SourceFile::SOURCE_CPP) ||
      used_types.Get(SourceFile::SOURCE_M) ||
      used_types.Get(SourceFile::SOURCE_MM)) {
    WriteOneFlag(target_, &CSubstitutionCFlags, false, Tool::kToolNone,
                 &ConfigValues::cflags, opts, path_output_, out_);
  }
  if (used_types.Get(SourceFile::SOURCE_C)) {
    WriteOneFlag(target_, &CSubstitutionCFlagsC, has_precompiled_headers,
                 CTool::kCToolCc, &ConfigValues::cflags_c, opts, path_output_,
                 out_);
  }
  if (used_types.Get(SourceFile::SOURCE_CPP)) {
    WriteOneFlag(target_, &CSubstitutionCFlagsCc, has_precompiled_headers,
                 CTool::kCToolCxx, &ConfigValues::cflags_cc, opts, path_output_,
                 out_);
  }
  if (used_types.Get(SourceFile::SOURCE_M)) {
    WriteOneFlag(target_, &CSubstitutionCFlagsObjC, has_precompiled_headers,
                 CTool::kCToolObjC, &ConfigValues::cflags_objc, opts,
                 path_output_, out_);
  }
  if (used_types.Get(SourceFile::SOURCE_MM)) {
    WriteOneFlag(target_, &CSubstitutionCFlagsObjCc, has_precompiled_headers,
                 CTool::kCToolObjCxx, &ConfigValues::cflags_objcc, opts,
                 path_output_, out_);
  }

  WriteSharedVars(subst);
}

OutputFile NinjaCBinaryTargetWriter::WriteInputsStampAndGetDep() const {
  CHECK(target_->toolchain()) << "Toolchain not set on target "
                              << target_->label().GetUserVisibleName(true);

  std::vector<const SourceFile*> inputs;
  for (ConfigValuesIterator iter(target_); !iter.done(); iter.Next()) {
    for (const auto& input : iter.cur().inputs()) {
      inputs.push_back(&input);
    }
  }

  if (inputs.size() == 0)
    return OutputFile();  // No inputs

  // If we only have one input, return it directly instead of writing a stamp
  // file for it.
  if (inputs.size() == 1)
    return OutputFile(settings_->build_settings(), *inputs[0]);

  // Make a stamp file.
  OutputFile input_stamp_file =
      GetBuildDirForTargetAsOutputFile(target_, BuildDirType::OBJ);
  input_stamp_file.value().append(target_->label().name());
  input_stamp_file.value().append(".inputs.stamp");

  out_ << "build ";
  path_output_.WriteFile(out_, input_stamp_file);
  out_ << ": " << GetNinjaRulePrefixForToolchain(settings_)
       << GeneralTool::kGeneralToolStamp;

  // File inputs.
  for (const auto* input : inputs) {
    out_ << " ";
    path_output_.WriteFile(out_, *input);
  }

  out_ << "\n";
  return input_stamp_file;
}

void NinjaCBinaryTargetWriter::WritePCHCommands(
    const SourceFileTypeSet& used_types,
    const OutputFile& input_dep,
    const std::vector<OutputFile>& order_only_deps,
    std::vector<OutputFile>* object_files,
    std::vector<OutputFile>* other_files) {
  if (!target_->config_values().has_precompiled_headers())
    return;

  const CTool* tool_c = target_->toolchain()->GetToolAsC(CTool::kCToolCc);
  if (tool_c && tool_c->precompiled_header_type() != CTool::PCH_NONE &&
      used_types.Get(SourceFile::SOURCE_C)) {
    WritePCHCommand(&CSubstitutionCFlagsC, CTool::kCToolCc,
                    tool_c->precompiled_header_type(), input_dep,
                    order_only_deps, object_files, other_files);
  }
  const CTool* tool_cxx = target_->toolchain()->GetToolAsC(CTool::kCToolCxx);
  if (tool_cxx && tool_cxx->precompiled_header_type() != CTool::PCH_NONE &&
      used_types.Get(SourceFile::SOURCE_CPP)) {
    WritePCHCommand(&CSubstitutionCFlagsCc, CTool::kCToolCxx,
                    tool_cxx->precompiled_header_type(), input_dep,
                    order_only_deps, object_files, other_files);
  }

  const CTool* tool_objc = target_->toolchain()->GetToolAsC(CTool::kCToolObjC);
  if (tool_objc && tool_objc->precompiled_header_type() == CTool::PCH_GCC &&
      used_types.Get(SourceFile::SOURCE_M)) {
    WritePCHCommand(&CSubstitutionCFlagsObjC, CTool::kCToolObjC,
                    tool_objc->precompiled_header_type(), input_dep,
                    order_only_deps, object_files, other_files);
  }

  const CTool* tool_objcxx =
      target_->toolchain()->GetToolAsC(CTool::kCToolObjCxx);
  if (tool_objcxx && tool_objcxx->precompiled_header_type() == CTool::PCH_GCC &&
      used_types.Get(SourceFile::SOURCE_MM)) {
    WritePCHCommand(&CSubstitutionCFlagsObjCc, CTool::kCToolObjCxx,
                    tool_objcxx->precompiled_header_type(), input_dep,
                    order_only_deps, object_files, other_files);
  }
}

void NinjaCBinaryTargetWriter::WritePCHCommand(
    const Substitution* flag_type,
    const char* tool_name,
    CTool::PrecompiledHeaderType header_type,
    const OutputFile& input_dep,
    const std::vector<OutputFile>& order_only_deps,
    std::vector<OutputFile>* object_files,
    std::vector<OutputFile>* other_files) {
  switch (header_type) {
    case CTool::PCH_MSVC:
      WriteWindowsPCHCommand(flag_type, tool_name, input_dep, order_only_deps,
                             object_files);
      break;
    case CTool::PCH_GCC:
      WriteGCCPCHCommand(flag_type, tool_name, input_dep, order_only_deps,
                         other_files);
      break;
    case CTool::PCH_NONE:
      NOTREACHED() << "Cannot write a PCH command with no PCH header type";
      break;
  }
}

void NinjaCBinaryTargetWriter::WriteGCCPCHCommand(
    const Substitution* flag_type,
    const char* tool_name,
    const OutputFile& input_dep,
    const std::vector<OutputFile>& order_only_deps,
    std::vector<OutputFile>* gch_files) {
  // Compute the pch output file (it will be language-specific).
  std::vector<OutputFile> outputs;
  GetPCHOutputFiles(target_, tool_name, &outputs);
  if (outputs.empty())
    return;

  gch_files->insert(gch_files->end(), outputs.begin(), outputs.end());

  std::vector<OutputFile> extra_deps;
  if (!input_dep.value().empty())
    extra_deps.push_back(input_dep);

  // Build line to compile the file.
  WriteCompilerBuildLine(target_->config_values().precompiled_source(),
                         extra_deps, order_only_deps, tool_name, outputs);

  // This build line needs a custom language-specific flags value. Rule-specific
  // variables are just indented underneath the rule line.
  out_ << "  " << flag_type->ninja_name << " =";

  // Each substitution flag is overwritten in the target rule to replace the
  // implicitly generated -include flag with the -x <header lang> flag required
  // for .gch targets.
  EscapeOptions opts = GetFlagOptions();
  if (tool_name == CTool::kCToolCc) {
    RecursiveTargetConfigStringsToStream(target_, &ConfigValues::cflags_c, opts,
                                         out_);
  } else if (tool_name == CTool::kCToolCxx) {
    RecursiveTargetConfigStringsToStream(target_, &ConfigValues::cflags_cc,
                                         opts, out_);
  } else if (tool_name == CTool::kCToolObjC) {
    RecursiveTargetConfigStringsToStream(target_, &ConfigValues::cflags_objc,
                                         opts, out_);
  } else if (tool_name == CTool::kCToolObjCxx) {
    RecursiveTargetConfigStringsToStream(target_, &ConfigValues::cflags_objcc,
                                         opts, out_);
  }

  // Append the command to specify the language of the .gch file.
  out_ << " -x " << GetPCHLangForToolType(tool_name);

  // Write two blank lines to help separate the PCH build lines from the
  // regular source build lines.
  out_ << std::endl << std::endl;
}

void NinjaCBinaryTargetWriter::WriteWindowsPCHCommand(
    const Substitution* flag_type,
    const char* tool_name,
    const OutputFile& input_dep,
    const std::vector<OutputFile>& order_only_deps,
    std::vector<OutputFile>* object_files) {
  // Compute the pch output file (it will be language-specific).
  std::vector<OutputFile> outputs;
  GetPCHOutputFiles(target_, tool_name, &outputs);
  if (outputs.empty())
    return;

  object_files->insert(object_files->end(), outputs.begin(), outputs.end());

  std::vector<OutputFile> extra_deps;
  if (!input_dep.value().empty())
    extra_deps.push_back(input_dep);

  // Build line to compile the file.
  WriteCompilerBuildLine(target_->config_values().precompiled_source(),
                         extra_deps, order_only_deps, tool_name, outputs);

  // This build line needs a custom language-specific flags value. Rule-specific
  // variables are just indented underneath the rule line.
  out_ << "  " << flag_type->ninja_name << " =";

  // Append the command to generate the .pch file.
  // This adds the value to the existing flag instead of overwriting it.
  out_ << " ${" << flag_type->ninja_name << "}";
  out_ << " /Yc" << target_->config_values().precompiled_header();

  // Write two blank lines to help separate the PCH build lines from the
  // regular source build lines.
  out_ << std::endl << std::endl;
}

void NinjaCBinaryTargetWriter::WriteSources(
    const std::vector<OutputFile>& pch_deps,
    const OutputFile& input_dep,
    const std::vector<OutputFile>& order_only_deps,
    std::vector<OutputFile>* object_files,
    std::vector<SourceFile>* other_files) {
  object_files->reserve(object_files->size() + target_->sources().size());

  std::vector<OutputFile> tool_outputs;  // Prevent reallocation in loop.
  std::vector<OutputFile> deps;
  for (const auto& source : target_->sources()) {
    // Clear the vector but maintain the max capacity to prevent reallocations.
    deps.resize(0);
    const char* tool_name = Tool::kToolNone;
    if (!target_->GetOutputFilesForSource(source, &tool_name, &tool_outputs)) {
      if (source.type() == SourceFile::SOURCE_DEF)
        other_files->push_back(source);
      continue;  // No output for this source.
    }

    if (!input_dep.value().empty())
      deps.push_back(input_dep);

    if (tool_name != Tool::kToolNone) {
      // Only include PCH deps that correspond to the tool type, for instance,
      // do not specify target_name.precompile.cc.obj (a CXX PCH file) as a dep
      // for the output of a C tool type.
      //
      // This makes the assumption that pch_deps only contains pch output files
      // with the naming scheme specified in GetWindowsPCHObjectExtension or
      // GetGCCPCHOutputExtension.
      const CTool* tool = target_->toolchain()->GetToolAsC(tool_name);
      if (tool->precompiled_header_type() != CTool::PCH_NONE) {
        for (const auto& dep : pch_deps) {
          const std::string& output_value = dep.value();
          size_t extension_offset = FindExtensionOffset(output_value);
          if (extension_offset == std::string::npos)
            continue;
          std::string output_extension;
          if (tool->precompiled_header_type() == CTool::PCH_MSVC) {
            output_extension = GetWindowsPCHObjectExtension(
                tool_name, output_value.substr(extension_offset - 1));
          } else if (tool->precompiled_header_type() == CTool::PCH_GCC) {
            output_extension = GetGCCPCHOutputExtension(tool_name);
          }
          if (output_value.compare(
                  output_value.size() - output_extension.size(),
                  output_extension.size(), output_extension) == 0) {
            deps.push_back(dep);
          }
        }
      }
      WriteCompilerBuildLine(source, deps, order_only_deps, tool_name,
                             tool_outputs);
    }

    // It's theoretically possible for a compiler to produce more than one
    // output, but we'll only link to the first output.
    object_files->push_back(tool_outputs[0]);
  }
  out_ << std::endl;
}

void NinjaCBinaryTargetWriter::WriteCompilerBuildLine(
    const SourceFile& source,
    const std::vector<OutputFile>& extra_deps,
    const std::vector<OutputFile>& order_only_deps,
    const char* tool_name,
    const std::vector<OutputFile>& outputs) {
  out_ << "build";
  path_output_.WriteFiles(out_, outputs);

  out_ << ": " << rule_prefix_ << tool_name;
  out_ << " ";
  path_output_.WriteFile(out_, source);

  if (!extra_deps.empty()) {
    out_ << " |";
    path_output_.WriteFiles(out_, extra_deps);
  }

  if (!order_only_deps.empty()) {
    out_ << " ||";
    path_output_.WriteFiles(out_, order_only_deps);
  }
  out_ << std::endl;
}

void NinjaCBinaryTargetWriter::WriteLinkerStuff(
    const std::vector<OutputFile>& object_files,
    const std::vector<SourceFile>& other_files,
    const OutputFile& input_dep) {
  std::vector<OutputFile> output_files;
  SubstitutionWriter::ApplyListToLinkerAsOutputFile(
      target_, tool_, tool_->outputs(), &output_files);

  out_ << "build";
  path_output_.WriteFiles(out_, output_files);

  out_ << ": " << rule_prefix_
       << Tool::GetToolTypeForTargetFinalOutput(target_);

  UniqueVector<OutputFile> extra_object_files;
  UniqueVector<const Target*> linkable_deps;
  UniqueVector<const Target*> non_linkable_deps;
  GetDeps(&extra_object_files, &linkable_deps, &non_linkable_deps);

  // Object files.
  path_output_.WriteFiles(out_, object_files);
  path_output_.WriteFiles(out_, extra_object_files);

  // Dependencies.
  std::vector<OutputFile> implicit_deps;
  std::vector<OutputFile> solibs;
  for (const Target* cur : linkable_deps) {
    // All linkable deps should have a link output file.
    DCHECK(!cur->link_output_file().value().empty())
        << "No link output file for "
        << target_->label().GetUserVisibleName(false);

    if (cur->dependency_output_file().value() !=
        cur->link_output_file().value()) {
      // This is a shared library with separate link and deps files. Save for
      // later.
      implicit_deps.push_back(cur->dependency_output_file());
      solibs.push_back(cur->link_output_file());
    } else {
      // Normal case, just link to this target.
      out_ << " ";
      path_output_.WriteFile(out_, cur->link_output_file());
    }
  }

  const SourceFile* optional_def_file = nullptr;
  if (!other_files.empty()) {
    for (const SourceFile& src_file : other_files) {
      if (src_file.type() == SourceFile::SOURCE_DEF) {
        optional_def_file = &src_file;
        implicit_deps.push_back(
            OutputFile(settings_->build_settings(), src_file));
        break;  // Only one def file is allowed.
      }
    }
  }

  // Libraries specified by paths.
  const OrderedSet<LibFile>& libs = target_->all_libs();
  for (size_t i = 0; i < libs.size(); i++) {
    if (libs[i].is_source_file()) {
      implicit_deps.push_back(
          OutputFile(settings_->build_settings(), libs[i].source_file()));
    }
  }

  // The input dependency is only needed if there are no object files, as the
  // dependency is normally provided transitively by the source files.
  if (!input_dep.value().empty() && object_files.empty())
    implicit_deps.push_back(input_dep);

  // Append implicit dependencies collected above.
  if (!implicit_deps.empty()) {
    out_ << " |";
    path_output_.WriteFiles(out_, implicit_deps);
  }

  // Append data dependencies as order-only dependencies.
  //
  // This will include data dependencies and input dependencies (like when
  // this target depends on an action). Having the data dependencies in this
  // list ensures that the data is available at runtime when the user builds
  // this target.
  //
  // The action dependencies are not strictly necessary in this case. They
  // should also have been collected via the input deps stamp that each source
  // file has for an order-only dependency, and since this target depends on
  // the sources, there is already an implicit order-only dependency. However,
  // it's extra work to separate these out and there's no disadvantage to
  // listing them again.
  WriteOrderOnlyDependencies(non_linkable_deps);

  // End of the link "build" line.
  out_ << std::endl;

  // The remaining things go in the inner scope of the link line.
  if (target_->output_type() == Target::EXECUTABLE ||
      target_->output_type() == Target::SHARED_LIBRARY ||
      target_->output_type() == Target::LOADABLE_MODULE) {
    WriteLinkerFlags(optional_def_file);
    WriteLibs();
  } else if (target_->output_type() == Target::STATIC_LIBRARY) {
    out_ << "  arflags =";
    RecursiveTargetConfigStringsToStream(target_, &ConfigValues::arflags,
                                         GetFlagOptions(), out_);
    out_ << std::endl;
  }
  WriteOutputSubstitutions();
  WriteSolibs(solibs);
}

void NinjaCBinaryTargetWriter::WriteLinkerFlags(
    const SourceFile* optional_def_file) {
  out_ << "  ldflags =";

  // First the ldflags from the target and its config.
  RecursiveTargetConfigStringsToStream(target_, &ConfigValues::ldflags,
                                       GetFlagOptions(), out_);

  // Followed by library search paths that have been recursively pushed
  // through the dependency tree.
  const OrderedSet<SourceDir> all_lib_dirs = target_->all_lib_dirs();
  if (!all_lib_dirs.empty()) {
    // Since we're passing these on the command line to the linker and not
    // to Ninja, we need to do shell escaping.
    PathOutput lib_path_output(path_output_.current_dir(),
                               settings_->build_settings()->root_path_utf8(),
                               ESCAPE_NINJA_COMMAND);
    for (size_t i = 0; i < all_lib_dirs.size(); i++) {
      out_ << " " << tool_->lib_dir_switch();
      lib_path_output.WriteDir(out_, all_lib_dirs[i],
                               PathOutput::DIR_NO_LAST_SLASH);
    }
  }

  if (optional_def_file) {
    out_ << " /DEF:";
    path_output_.WriteFile(out_, *optional_def_file);
  }

  out_ << std::endl;
}

void NinjaCBinaryTargetWriter::WriteLibs() {
  out_ << "  libs =";

  // Libraries that have been recursively pushed through the dependency tree.
  EscapeOptions lib_escape_opts;
  lib_escape_opts.mode = ESCAPE_NINJA_COMMAND;
  const OrderedSet<LibFile> all_libs = target_->all_libs();
  const std::string framework_ending(".framework");
  for (size_t i = 0; i < all_libs.size(); i++) {
    const LibFile& lib_file = all_libs[i];
    const std::string& lib_value = lib_file.value();
    if (lib_file.is_source_file()) {
      out_ << " ";
      path_output_.WriteFile(out_, lib_file.source_file());
    } else if (base::EndsWith(lib_value, framework_ending,
                              base::CompareCase::INSENSITIVE_ASCII)) {
      // Special-case libraries ending in ".framework" to support Mac: Add the
      // -framework switch and don't add the extension to the output.
      out_ << " -framework ";
      EscapeStringToStream(
          out_, lib_value.substr(0, lib_value.size() - framework_ending.size()),
          lib_escape_opts);
    } else {
      out_ << " " << tool_->lib_switch();
      EscapeStringToStream(out_, lib_value, lib_escape_opts);
    }
  }
  out_ << std::endl;
}

void NinjaCBinaryTargetWriter::WriteOutputSubstitutions() {
  out_ << "  output_extension = "
       << SubstitutionWriter::GetLinkerSubstitution(
              target_, tool_, &CSubstitutionOutputExtension);
  out_ << std::endl;
  out_ << "  output_dir = "
       << SubstitutionWriter::GetLinkerSubstitution(target_, tool_,
                                                    &CSubstitutionOutputDir);
  out_ << std::endl;
}

void NinjaCBinaryTargetWriter::WriteSolibs(
    const std::vector<OutputFile>& solibs) {
  if (solibs.empty())
    return;

  out_ << "  solibs =";
  path_output_.WriteFiles(out_, solibs);
  out_ << std::endl;
}

void NinjaCBinaryTargetWriter::WriteSourceSetStamp(
    const std::vector<OutputFile>& object_files) {
  // The stamp rule for source sets is generally not used, since targets that
  // depend on this will reference the object files directly. However, writing
  // this rule allows the user to type the name of the target and get a build
  // which can be convenient for development.
  UniqueVector<OutputFile> extra_object_files;
  UniqueVector<const Target*> linkable_deps;
  UniqueVector<const Target*> non_linkable_deps;
  GetDeps(&extra_object_files, &linkable_deps, &non_linkable_deps);

  // The classifier should never put extra object files in a source set:
  // any source sets that we depend on should appear in our non-linkable
  // deps instead.
  DCHECK(extra_object_files.empty());

  std::vector<OutputFile> order_only_deps;
  for (auto* dep : non_linkable_deps)
    order_only_deps.push_back(dep->dependency_output_file());

  WriteStampForTarget(object_files, order_only_deps);
}

void NinjaCBinaryTargetWriter::GetDeps(
    UniqueVector<OutputFile>* extra_object_files,
    UniqueVector<const Target*>* linkable_deps,
    UniqueVector<const Target*>* non_linkable_deps) const {
  // Normal public/private deps.
  for (const auto& pair : target_->GetDeps(Target::DEPS_LINKED)) {
    ClassifyDependency(pair.ptr, extra_object_files, linkable_deps,
                       non_linkable_deps);
  }

  // Inherited libraries.
  for (auto* inherited_target : target_->inherited_libraries().GetOrdered()) {
    ClassifyDependency(inherited_target, extra_object_files, linkable_deps,
                       non_linkable_deps);
  }

  // Data deps.
  for (const auto& data_dep_pair : target_->data_deps())
    non_linkable_deps->push_back(data_dep_pair.ptr);
}

void NinjaCBinaryTargetWriter::ClassifyDependency(
    const Target* dep,
    UniqueVector<OutputFile>* extra_object_files,
    UniqueVector<const Target*>* linkable_deps,
    UniqueVector<const Target*>* non_linkable_deps) const {
  // Only the following types of outputs have libraries linked into them:
  //  EXECUTABLE
  //  SHARED_LIBRARY
  //  _complete_ STATIC_LIBRARY
  //
  // Child deps of intermediate static libraries get pushed up the
  // dependency tree until one of these is reached, and source sets
  // don't link at all.
  bool can_link_libs = target_->IsFinal();

  if (dep->output_type() == Target::SOURCE_SET ||
      // If a complete static library depends on an incomplete static library,
      // manually link in the object files of the dependent library as if it
      // were a source set. This avoids problems with braindead tools such as
      // ar which don't properly link dependent static libraries.
      (target_->complete_static_lib() &&
       dep->output_type() == Target::STATIC_LIBRARY &&
       !dep->complete_static_lib())) {
    // Source sets have their object files linked into final targets
    // (shared libraries, executables, loadable modules, and complete static
    // libraries). Intermediate static libraries and other source sets
    // just forward the dependency, otherwise the files in the source
    // set can easily get linked more than once which will cause
    // multiple definition errors.
    if (can_link_libs)
      AddSourceSetObjectFiles(dep, extra_object_files);

    // Add the source set itself as a non-linkable dependency on the current
    // target. This will make sure that anything the source set's stamp file
    // depends on (like data deps) are also built before the current target
    // can be complete. Otherwise, these will be skipped since this target
    // will depend only on the source set's object files.
    non_linkable_deps->push_back(dep);
  } else if (target_->complete_static_lib() && dep->IsFinal()) {
    non_linkable_deps->push_back(dep);
  } else if (can_link_libs && dep->IsLinkable()) {
    linkable_deps->push_back(dep);
  } else {
    non_linkable_deps->push_back(dep);
  }
}

void NinjaCBinaryTargetWriter::WriteOrderOnlyDependencies(
    const UniqueVector<const Target*>& non_linkable_deps) {
  if (!non_linkable_deps.empty()) {
    out_ << " ||";

    // Non-linkable targets.
    for (auto* non_linkable_dep : non_linkable_deps) {
      out_ << " ";
      path_output_.WriteFile(out_, non_linkable_dep->dependency_output_file());
    }
  }
}

bool NinjaCBinaryTargetWriter::CheckForDuplicateObjectFiles(
    const std::vector<OutputFile>& files) const {
  std::unordered_set<std::string> set;
  for (const auto& file : files) {
    if (!set.insert(file.value()).second) {
      Err err(
          target_->defined_from(), "Duplicate object file",
          "The target " + target_->label().GetUserVisibleName(false) +
              "\ngenerates two object files with the same name:\n  " +
              file.value() +
              "\n"
              "\n"
              "It could be you accidentally have a file listed twice in the\n"
              "sources. Or, depending on how your toolchain maps sources to\n"
              "object files, two source files with the same name in different\n"
              "directories could map to the same object file.\n"
              "\n"
              "In the latter case, either rename one of the files or move one "
              "of\n"
              "the sources to a separate source_set to avoid them both being "
              "in\n"
              "the same target.");
      g_scheduler->FailWithError(err);
      return false;
    }
  }
  return true;
}