'recipes.py isolate' command to build an isolate of the current package's toolchain

recipes.py

Index: recipes.py
diff --git a/recipes.py b/recipes.py
index 5f6a2091752e774da566aa7db97a8df0e558ab6b..c8a6d1ebdb5980173689f28a8111c0fe0de83953 100755
--- a/recipes.py
+++ b/recipes.py
@@ -218,6 +218,34 @@ def info(args):
     print package_spec.recipes_path
 
 
+def isolate(package_deps, args):
+  from recipe_engine import package
+
+  repo_root, config_file = get_package_config(args)
+  context = package.PackageContext.from_proto_file(repo_root, config_file)
+  base_path = package_deps.root_package.recipes_dir
+  def norm(p):
+    return os.path.relpath(p, base_path)
+  recipes_tool = norm(os.path.join(
+      package_deps.get_package('recipe_engine').recipes_dir,
+      'recipes.py'))
+
+  overrides = [ '-O %s=%s' % (k, norm(v))
+                for k,v in args.project_override.iteritems() ]
+
+  print json.dumps({
+    'variables': {
+      'files': [norm(f) for f in package_deps.root_package.all_files(context)],
+      'command': [
+        'python',
+        recipes_tool,
+        '--package', norm(
+            package_deps.root_package.repo_spec.proto_file(context).path),
+        '--no-fetch',
+      ] + overrides,
+    },
+  }, indent=2, separators=(',', ': '))
+
 def main():
   from recipe_engine import package
 
@@ -244,6 +272,7 @@ def main():
       help='Path to the script used to bootstrap this tool (internal use only)')
   parser.add_argument('-O', '--project-override', metavar='ID=PATH',
       action=ProjectOverrideAction,
+      default={},
       help='Override a project repository path with a local one.')
 
   subp = parser.add_subparsers()
@@ -315,6 +344,12 @@ def main():
       '--recipes-dir', action='store_true',
       help='Get the subpath where the recipes live relative to repository root')
 
+  isolate_p = subp.add_parser(
+      'isolate',
+      help='Write an isolate file to stdout for the recipe toolchain of the '
+           'current project')
+  isolate_p.set_defaults(command='isolate')
+
   args = parser.parse_args()
 
   if args.verbose:
@@ -343,6 +378,8 @@ def main():
     return doc(package_deps, args)
   elif args.command == 'info':
     return info(args)
+  elif args.command == 'isolate':
+    return isolate(package_deps, args)
   else:
     print """Dear sir or madam,
         It has come to my attention that a quite impossible condition has come