Automatically generate externs.js for a format (idl, json) supported by tools/json_schema_compiler.

tools/json_schema_compiler/compiler.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 """Generator for C++ structs from api json files.
 
 The purpose of this tool is to remove the need for hand-written code that
 converts to and from base::Value types when receiving javascript api calls.
 Originally written for generating code for extension apis. Reference schemas
 are in chrome/common/extensions/api.
 
 Usage example:
   compiler.py --root /home/Work/src --namespace extensions windows.json
     tabs.json
   compiler.py --destdir gen --root /home/Work/src
     --namespace extensions windows.json tabs.json
 """
 
 import optparse
 import os
 import shlex
 import sys
 
 from cpp_bundle_generator import CppBundleGenerator
 from cpp_generator import CppGenerator
 from cpp_type_generator import CppTypeGenerator
 from dart_generator import DartGenerator
+from externs_js_generator import ExternsJsGenerator
 import json_schema
 from cpp_namespace_environment import CppNamespaceEnvironment
 from model import Model
 from schema_loader import SchemaLoader
 
 # Names of supported code generators, as specified on the command-line.
 # First is default.
-GENERATORS = ['cpp', 'cpp-bundle-registration', 'cpp-bundle-schema', 'dart']
+GENERATORS = [
+    'cpp', 'cpp-bundle-registration', 'cpp-bundle-schema', 'dart', 'externs-js']
 
 def GenerateSchema(generator_name,
                    file_paths,
                    root,
                    destdir,
                    cpp_namespace_pattern,
                    dart_overrides_dir,
                    impl_dir,
                    include_rules):
   # Merge the source files into a single list of schemas.
@@ skipping 69 matching lines @@
     cpp_generator = CppGenerator(type_generator)
     generators = [
       ('%s.h' % filename_base, cpp_generator.h_generator),
       ('%s.cc' % filename_base, cpp_generator.cc_generator)
     ]
   elif generator_name == 'dart':
     generators = [
       ('%s.dart' % namespace.unix_name, DartGenerator(
           dart_overrides_dir))
     ]
+  elif generator_name == 'externs-js':
+    generators = [('externs.js', ExternsJsGenerator())]
   else:
     raise Exception('Unrecognised generator %s' % generator)
 
   output_code = []
   for filename, generator in generators:
     code = generator.Generate(namespace).Render()
     if destdir:
       if generator_name == 'cpp-bundle-registration':
         # Function registrations must be output to impl_dir, since they link in
         # API implementations.
@@ skipping 54 matching lines @@
   include_rules = []
   if opts.include_rules:
     include_rules = map(split_path_and_namespace,
                         shlex.split(opts.include_rules))
 
   result = GenerateSchema(opts.generator, file_paths, opts.root, opts.destdir,
                           opts.namespace, opts.dart_overrides_dir,
                           opts.impl_dir, include_rules)
   if not opts.destdir:
     print result