Add initial prototype for the GN meta-buildsystem.

tools/gn/settings.h

Index: tools/gn/settings.h
diff --git a/tools/gn/settings.h b/tools/gn/settings.h
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+// 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.
+
+#ifndef TOOLS_GN_SETTINGS_H_
+#define TOOLS_GN_SETTINGS_H_
+
+#include "base/files/file_path.h"
+#include "tools/gn/build_settings.h"
+#include "tools/gn/import_manager.h"
+#include "tools/gn/output_file.h"
+#include "tools/gn/scope.h"
+#include "tools/gn/source_dir.h"
+#include "tools/gn/toolchain.h"
+
+// Holds the settings for one toolchain invocation. There will be one
+// Settings object for each toolchain type, each referring to the same
+// BuildSettings object for shared stuff.
+//
+// The Settings object is const once it is constructed, which allows us to
+// use it from multiple threads during target generation without locking (which
+// is important, because it gets used a lot).
+//
+// The Toolchain object holds the set of stuff that is set by the toolchain
+// declaration, which obviously needs to be set later when we actually parse
+// the file with the toolchain declaration in it.
+class Settings {
+ public:
+  enum TargetOS {
+    UNKNOWN,
+    LINUX,
+    MAC,
+    WIN
+  };
+
+  // Constructs a toolchain settings. The output_subdir_name is the name we
+  // should use for the subdirectory in the build output directory for this
+  // toolchain's outputs. It should have no slashes in it. The default
+  // toolchain should use an empty string.
+  Settings(const BuildSettings* build_settings,
+           const Toolchain* toolchain,
+           const std::string& output_subdir_name);
+  ~Settings();
+
+  const BuildSettings* build_settings() const { return build_settings_; }
+
+  // Danger: this must only be used for getting the toolchain label until the
+  // toolchain has been resolved. Otherwise, it will be modified on an
+  // arbitrary thread when the toolchain invocation is found. Generally, you
+  // will only read this from the target generation where we know everything
+  // has been resolved and won't change.
+  const Toolchain* toolchain() const { return toolchain_; }
+
+  bool IsMac() const { return target_os_ == MAC; }
+  bool IsWin() const { return target_os_ == WIN; }
+
+  TargetOS target_os() const { return target_os_; }
+  void set_target_os(TargetOS t) { target_os_ = t; }
+
+  const OutputFile& toolchain_output_subdir() const {
+    return toolchain_output_subdir_;
+  }
+  const SourceDir& toolchain_output_dir() const {
+    return toolchain_output_dir_;
+  }
+
+  // Directory for generated files.
+  const SourceDir& toolchain_gen_dir() const {
+    return toolchain_gen_dir_;
+  }
+
+  // The import manager caches the result of executing imported files in the
+  // context of a given settings object.
+  //
+  // See the ItemTree getter in GlobalSettings for why this doesn't return a
+  // const pointer.
+  ImportManager& import_manager() const { return import_manager_; }
+
+  const Scope* base_config() const { return &base_config_; }
+  Scope* base_config() { return &base_config_; }
+
+ private:
+  const BuildSettings* build_settings_;
+
+  const Toolchain* toolchain_;
+
+  TargetOS target_os_;
+
+  mutable ImportManager import_manager_;
+
+  // The subdirectory inside the build output for this toolchain. For the
+  // default toolchain, this will be empty (since the deafult toolchain's
+  // output directory is the same as the build directory). When nonempty, this
+  // is guaranteed to end in a slash.
+  OutputFile toolchain_output_subdir_;
+
+  // Full source file path to the toolchain output directory.
+  SourceDir toolchain_output_dir_;
+
+  SourceDir toolchain_gen_dir_;
+
+  Scope base_config_;
+
+  DISALLOW_COPY_AND_ASSIGN(Settings);
+};
+
+#endif  // TOOLS_GN_SETTINGS_H_