Fix typos and error handling in setup_dart_analyzer

sky/tools/setup-dart-analyzer

-#!/usr/bin/env python
-# Copyright 2015 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.
-
-import argparse
-import subprocess
-import sys
-import os
-import yaml
-
-
-SKY_TOOLS_DIR = os.path.dirname(os.path.abspath(__file__))
-SRC_ROOT = os.path.dirname(os.path.dirname(SKY_TOOLS_DIR))
-SKY_SDK_DIR = os.path.join(SRC_ROOT, 'sky', 'sdk')
-SKY_PUBSPEC = os.path.join(SKY_SDK_DIR, 'pubspec.yaml')
-SKY_PUBSPEC_LOCK = os.path.join(SKY_SDK_DIR, 'pubspec.lock')
-SDK_EXT = os.path.join(SKY_SDK_DIR, 'lib', '_sdkext')
-
-SDK_EXT_TEMPLATE = '''{
-  "dart:sky": "%(build_dir)s/gen/dart-pkg/sky/sdk_ext/dart_sky.dart",
-  "dart:sky.internals": "%(build_dir)s/gen/dart-pkg/sky/sky_internals.dart",
-  "dart:sky_builtin_natvies": "%(build_dir)s../sdk_ext/builtin_natives.dart"
-}'''
-
-def version_for_pubspec(pubspec_path):
-    with open(pubspec_path, 'r') as stream:
-        dependency_spec = yaml.load(stream)
-        return dependency_spec['version']
-
-
-def entry_for_dependency(dart_pkg_dir, dependency):
-    dependency_path = os.path.join(dart_pkg_dir, dependency)
-    version = version_for_pubspec(os.path.join(dependency_path, 'pubspec.yaml'))
-    return {
-        'description': {
-            'path': os.path.relpath(dependency_path, SKY_SDK_DIR),
-            'relative': True,
-        },
-        'source': 'path',
-        'version': version,
-    }
-
-
-def main():
-    parser = argparse.ArgumentParser(description='Adds files to the source tree to make the dart analyzer happy')
-    parser.add_argument('build_dir', type=str, help='Path the build directory to use for build artifacts')
-    args = parser.parse_args()
-
-    dart_pkg_dir = os.path.join(args.build_dir, 'gen', 'dart-pkg')
-    packages = {}
-
-    with open(SKY_PUBSPEC, 'r') as stream:
-        spec = yaml.load(stream)
-        for dependency in spec['dependencies'].keys():
-            packages[dependency] = entry_for_dependency(dart_pkg_dir, dependency)
-
-    lock = { 'packages': packages }
-    with open(SKY_PUBSPEC_LOCK, 'w') as stream:
-        yaml.dump(lock, stream=stream, default_flow_style=False)
-
-    with open(SDK_EXT, 'w') as stream:
-        rebased_build_dir = os.path.relpath(args.build_dir, os.path.dirname(SDK_EXT))
-        stream.write(SDK_EXT_TEMPLATE % { 'build_dir': rebased_build_dir })
-
-
-if __name__ == '__main__':
-    sys.exit(main())