Automatically discover the mojoconfig file.

mojo/devtools/common/devtoolslib/shell_config.py

 # 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.
 
 """Configuration for the shell abstraction.
 
 This module declares ShellConfig and knows how to compute it from command-line
 arguments, applying any default paths inferred from the checkout, configuration
 file, etc.
 """
@@ skipping 72 matching lines @@
       'These arguments apply only when running on desktop.')
   desktop_group.add_argument('--use-osmesa', action='store_true',
                              help='Configure the native viewport service '
                              'for off-screen rendering.')
 
   config_file_group = parser.add_argument_group('Configuration file',
       'These arguments allow to modify the behavior regarding the mojoconfig '
       'file.')
   config_file_group.add_argument('--config-file', type=file,
                                  help='Path of the configuration file to use.')
+  config_file_group.add_argument('--no-config-file', action='store_true',
+                                 help='Pass to skip automatic discovery of the '
+                                 'mojoconfig file.')
 
   # Arguments allowing to indicate the build directory we are targeting when
   # running within a Chromium-like checkout (e.g. Mojo checkout). These will go
   # away once we have devtools config files, see
   # https://github.com/domokit/devtools/issues/28.
   chromium_checkout_group = parser.add_argument_group(
       'Chromium-like checkout configuration',
       'These arguments allow to infer paths to tools and build results '
       'when running within a Chromium-like checkout')
   debug_group = chromium_checkout_group.add_mutually_exclusive_group()
   debug_group.add_argument('--debug', help='Debug build (default)',
                            default=True, action='store_true')
   debug_group.add_argument('--release', help='Release build', default=False,
                            dest='debug', action='store_false')
   chromium_checkout_group.add_argument('--target-cpu',
                                      help='CPU architecture to run for.',
                                      choices=['x64', 'x86', 'arm'])
 
 
+def _discover_config_file():
+  config_file_path = paths.find_within_ancestors('mojoconfig')
+  if not config_file_path:
+    return None
+  return open(config_file_path)
+
+
 def _read_config_file(config_file, aliases):
   spec = config_file.read()
   for alias_pattern, alias_value in aliases:
     spec = spec.replace(alias_pattern, alias_value)
   return ast.literal_eval(spec)
 
 
 def get_shell_config(script_args):
   """Processes command-line options defined in add_shell_arguments(), applying
   any inferred default paths and produces an instance of ShellConfig.
@@ skipping 22 matching lines @@
   shell_config.logcat_tags = script_args.logcat_tags
 
   # Desktop-only.
   shell_config.use_osmesa = script_args.use_osmesa
 
   if (shell_config.android and not shell_config.origin and
       inferred_paths['build_dir_path']):
     shell_config.origin = inferred_paths['build_dir_path']
 
   # Read the mojoconfig file.
-  if script_args.config_file:
+  config_file = script_args.config_file
+  if not script_args.no_config_file:
+    config_file = config_file or _discover_config_file()
+
+  if config_file:

[qsr, 2015/08/05 11:50:59]

Can you use:
with config_file:
inside the if (to not have to worry about closing... Or won't it work with
argparse file object?

[ppi, 2015/08/05 11:55:44]

Seems to be working fine, done.

     config_file_aliases = []
     if inferred_paths['build_dir_path']:
       config_file_aliases.append(('@{BUILD_DIR}',
                                   inferred_paths['build_dir_path']))
 
-    mojoconfig = None
+    config = None
     try:
-      mojoconfig = _read_config_file(script_args.config_file,
-                                     config_file_aliases)
+      if script_args.verbose:
+        print 'Reading config file from: ' + config_file.name
+      config = _read_config_file(config_file, config_file_aliases)
+      config_file.close()
     except SyntaxError:
       raise ShellConfigurationException('Failed to parse the mojoconfig file.')
 
-    if 'dev_servers' in mojoconfig:
+    if 'dev_servers' in config:
       try:
-        for dev_server_spec in mojoconfig['dev_servers']:
+        for dev_server_spec in config['dev_servers']:
           dev_server_config = DevServerConfig()
           dev_server_config.host = dev_server_spec['host']
           dev_server_config.mappings = []
           for prefix, path in dev_server_spec['mappings']:
             dev_server_config.mappings.append((prefix, path))
           shell_config.dev_servers.append(dev_server_config)
       except (ValueError, KeyError):
         raise ShellConfigurationException('Failed to parse dev_servers in '
                                           'the mojoconfig file.')
   return shell_config