Make output placeholders like json.output index-able by name.

recipe_engine/util.py

 # Copyright 2013-2015 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 contextlib
 import functools
 import os
 import sys
 import traceback
 import urllib
@@ skipping 16 matching lines @@
     if self.owner_module is None:
       raise ModuleInjectionError(
         "RecipeApi has no dependency %r. (Add it to DEPS?)" % (key,))
     else:
       raise ModuleInjectionError(
         "Recipe Module %r has no dependency %r. (Add it to __init__.py:DEPS?)"
         % (self.owner_module.name, key))
 
 
 class Placeholder(object):
+  DEFAULT_ID = object()
+
   """Base class for json placeholders. Do not use directly."""
-  def __init__(self):
+  def __init__(self, id=None):

[iannucci, 2016/03/10 03:17:42]

I think you can do

  id=DEFAULT_ID

or maybe
  
  id=Placeholder.DEFAULT_ID

?

[stgao, 2016/03/10 20:34:23]

No. We can't do that, because subclasses will call this with id=None and
id=DEFAULT_ID here won't work in that case.

     self.name_pieces = None
+    self.id = id or Placeholder.DEFAULT_ID
 
   @property
   def backing_file(self):  # pragma: no cover
     """Return path to a temp file that holds or receives the data.
 
     Valid only after 'render' has been called.
     """
     raise NotImplementedError
 
   def render(self, test):  # pragma: no cover
@@ skipping 11 matching lines @@
 
     May optionally modify presentation as a side-effect.
     """
     pass
 
   @property
   def name(self):
     assert self.name_pieces
     return "%s.%s" % self.name_pieces
 
+  @property
+  def id_name(self):
+    if self.id == self.DEFAULT_ID:

[iannucci, 2016/03/10 03:17:42]

use the `is` keyword for comparison (compares pointer)

[stgao, 2016/03/10 20:34:23]

Done.

+      return self.name
+    else:
+      return "%s.%s" % (self.id, self.name)
 
 def static_wraps(func):
   wrapped_fn = func
   if isinstance(func, staticmethod):
     # __get__(obj) is the way to get the function contained in the staticmethod.
     # python 2.7+ has a __func__ member, but previous to this the attribute
     # doesn't exist. It doesn't matter what the obj is, as long as it's not
     # None.
     wrapped_fn = func.__get__(object)
   return functools.wraps(wrapped_fn)
@@ skipping 83 matching lines @@
         self.lines[-1].write(s)
         break
       self.lines[-1].write(s[:i])
       self.lines[-1] = self.lines[-1].getvalue()
       self.lines.append(StringIO())
       s = s[i+1:]
 
   def close(self):
     if not isinstance(self.lines[-1], basestring):
       self.lines[-1] = self.lines[-1].getvalue()