[GN] Add JSON project writer

tools/gn/json_project_writer.cc

Index: tools/gn/json_project_writer.cc
diff --git a/tools/gn/json_project_writer.cc b/tools/gn/json_project_writer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..00cee9a5229ada212547c9c66af7954e63b573bc
--- /dev/null
+++ b/tools/gn/json_project_writer.cc
@@ -0,0 +1,138 @@
+// Copyright (c) 2016 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/json_project_writer.h"
+
+#include <iostream>
+
+#include "base/command_line.h"
+#include "base/json/json_writer.h"
+#include "base/memory/ptr_util.h"
+#include "base/strings/string_number_conversions.h"
+#include "tools/gn/builder.h"
+#include "tools/gn/desc_builder.h"
+#include "tools/gn/exec_process.h"
+#include "tools/gn/filesystem_utils.h"
+#include "tools/gn/settings.h"
+
+namespace {
+
+std::string render_json(const BuildSettings* build_settings,
+                        const Builder* builder) {
+  std::vector<const Target*> all_targets = builder->GetAllResolvedTargets();
+
+  Label default_toolchain_label;
+
+  auto targets = base::WrapUnique(new base::DictionaryValue());
+  for (const auto* target : all_targets) {
+    if (default_toolchain_label.is_null())
+      default_toolchain_label = target->settings()->default_toolchain_label();
+    targets->Set(
+        target->label().GetUserVisibleName(default_toolchain_label),
+        DescBuilder::DescriptionForTarget(target, "", false, false, false));
+  }
+
+  auto settings = base::WrapUnique(new base::DictionaryValue());
+  settings->SetString("root_path", build_settings->root_path_utf8());
+  settings->SetString("build_dir", build_settings->build_dir().value());
+  settings->SetString("default_toolchain",
+                      default_toolchain_label.GetUserVisibleName(false));
+
+  auto output = base::WrapUnique(new base::DictionaryValue());
+  output->Set("targets", std::move(targets));
+  output->Set("build_settings", std::move(settings));
+
+  std::string s;
+  base::JSONWriter::WriteWithOptions(
+      *output.get(), base::JSONWriter::OPTIONS_PRETTY_PRINT, &s);
+  return s;
+}
+
+bool invoke_python(const BuildSettings* build_settings,
+                   const base::FilePath& python_script_path,
+                   const std::string& python_script_extra_args,
+                   const base::FilePath& output_path,
+                   bool quiet,
+                   Err* err) {
+  const base::FilePath& python_path = build_settings->python_path();
+  base::CommandLine cmdline(python_path);
+  cmdline.AppendArg("--");
+  cmdline.AppendArgPath(python_script_path);
+  cmdline.AppendArgPath(output_path);
+  if (!python_script_extra_args.empty()) {
+    cmdline.AppendArg(python_script_extra_args);
+  }
+  base::FilePath startup_dir =
+      build_settings->GetFullPath(build_settings->build_dir());
+
+  std::string output;
+  std::string stderr_output;
+
+  int exit_code = 0;
+  if (!internal::ExecProcess(cmdline, startup_dir, &output, &stderr_output,
+                             &exit_code)) {
+    *err =
+        Err(Location(), "Could not execute python.",
+            "I was trying to execute \"" + FilePathToUTF8(python_path) + "\".");
+    return false;
+  }
+
+  if (!quiet) {
+    std::cout << output;
+    std::cerr << stderr_output;
+  }
+
+  if (exit_code != 0) {
+    *err = Err(Location(), "Python has quit with exit code " +
+                               base::IntToString(exit_code) + ".");
+    return false;
+  }
+
+  return true;
+}
+
+}  // namespace
+
+bool JSONProjectWriter::RunAndWriteFiles(
+    const BuildSettings* build_settings,
+    const Builder* builder,
+    const std::string& file_name,
+    const std::string& exec_script,
+    const std::string& exec_script_extra_args,
+    bool quiet,
+    Err* err) {
+  SourceFile output_file = build_settings->build_dir().ResolveRelativeFile(
+      Value(nullptr, file_name), err);
+  if (output_file.is_null()) {
+    return false;
+  }
+
+  base::FilePath output_path = build_settings->GetFullPath(output_file);
+
+  std::string json = render_json(build_settings, builder);
+  if (!ContentsEqual(output_path, json)) {
+    if (!WriteFileIfChanged(output_path, json, err)) {
+      return false;
+    }
+
+    if (!exec_script.empty()) {
+      SourceFile script_file;
+      if (exec_script[0] != '/') {
+        // relative path, assume the base is in build_dir
+        script_file = build_settings->build_dir().ResolveRelativeFile(
+            Value(nullptr, exec_script), err);
+        if (script_file.is_null()) {
+          return false;
+        }
+      } else {
+        script_file = SourceFile(exec_script);
+      }
+      base::FilePath script_path = build_settings->GetFullPath(script_file);
+      return invoke_python(build_settings, script_path, exec_script_extra_args,
+                           output_path, quiet, err);
+    }
+  }
+
+  return true;
+}