Add initial prototype for the GN meta-buildsystem.

tools/gn/scope_per_file_provider.h

Index: tools/gn/scope_per_file_provider.h
diff --git a/tools/gn/scope_per_file_provider.h b/tools/gn/scope_per_file_provider.h
new file mode 100644
index 0000000000000000000000000000000000000000..1edb7690aae062b7e57d3785191fd1dad2eea9dc
--- /dev/null
+++ b/tools/gn/scope_per_file_provider.h
@@ -0,0 +1,79 @@
+// 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_SCOPE_PER_FILE_PROVIDER_H_
+#define TOOLS_GN_SCOPE_PER_FILE_PROVIDER_H_
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "tools/gn/scope.h"
+#include "tools/gn/source_file.h"
+
+// ProgrammaticProvider for a scope to provide it with per-file built-in
+// variable support.
+class ScopePerFileProvider : public Scope::ProgrammaticProvider {
+ public:
+  ScopePerFileProvider(Scope* scope, const SourceFile& source_file);
+  virtual ~ScopePerFileProvider();
+
+  // ProgrammaticProvider implementation.
+  virtual const Value* GetProgrammaticValue(
+      const base::StringPiece& ident) OVERRIDE;
+
+  // Returns the value to expose to script for the given thing. These values
+  // are acually set globally, but are put here so we can keep all logic
+  // for converting paths to built-in values in this one file.
+  static Value GetRootOutputDir(const Settings* settings);
+  static Value GetRootGenDir(const Settings* settings);
+
+  // Variable names. These two should be set globally independent of the file
+  // being processed.
+  static const char* kRootOutputDirName;
+  static const char* kRootGenDirName;
+
+  // Variable names. These are provided by this class as needed.
+  static const char* kDefaultToolchain;
+  static const char* kPythonPath;
+  static const char* kToolchain;
+  static const char* kTargetOutputDirName;
+  static const char* kTargetGenDirName;
+  static const char* kRelativeRootOutputDirName;
+  static const char* kRelativeRootGenDirName;
+  static const char* kRelativeTargetOutputDirName;
+  static const char* kRelativeTargetGenDirName;
+
+ private:
+  const Value* GetDefaultToolchain();
+  const Value* GetPythonPath();
+  const Value* GetToolchain();
+  const Value* GetTargetOutputDir();
+  const Value* GetTargetGenDir();
+  const Value* GetRelativeRootOutputDir();
+  const Value* GetRelativeRootGenDir();
+  const Value* GetRelativeTargetOutputDir();
+  const Value* GetRelativeTargetGenDir();
+
+  static std::string GetRootOutputDirWithNoLastSlash(const Settings* settings);
+  static std::string GetRootGenDirWithNoLastSlash(const Settings* settings);
+
+  std::string GetFileDirWithNoLastSlash() const;
+  std::string GetRelativeRootWithNoLastSlash() const;
+
+  SourceFile source_file_;
+
+  // All values are lazily created.
+  scoped_ptr<Value> default_toolchain_;
+  scoped_ptr<Value> python_path_;
+  scoped_ptr<Value> toolchain_;
+  scoped_ptr<Value> target_output_dir_;
+  scoped_ptr<Value> target_gen_dir_;
+  scoped_ptr<Value> relative_root_output_dir_;
+  scoped_ptr<Value> relative_root_gen_dir_;
+  scoped_ptr<Value> relative_target_output_dir_;
+  scoped_ptr<Value> relative_target_gen_dir_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopePerFileProvider);
+};
+
+#endif  // TOOLS_GN_SCOPE_PER_FILE_PROVIDER_H_