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

recipe_engine/step_runner.py

Index: recipe_engine/step_runner.py
diff --git a/recipe_engine/step_runner.py b/recipe_engine/step_runner.py
index 2cd05d3576c4bacd0c501c2156d871dbcdeecd83..f9a9e71ebf1fb7ecf415fbcd7dacd8ee472b087a 100644
--- a/recipe_engine/step_runner.py
+++ b/recipe_engine/step_runner.py
@@ -448,14 +448,20 @@ def render_step(step, step_test):
   rendered_step = dict(step)
 
   # Process 'cmd', rendering placeholders there.
-  placeholders = collections.defaultdict(lambda: collections.defaultdict(list))
+  placeholders = collections.defaultdict(
+      lambda: collections.defaultdict(collections.OrderedDict))
   new_cmd = []
   for item in step.get('cmd', []):
     if isinstance(item, util.Placeholder):
       module_name, placeholder_name = item.name_pieces
-      tdata = step_test.pop_placeholder(item.name_pieces)
+      tdata = step_test.pop_placeholder(module_name, placeholder_name, item.id)
       new_cmd.extend(item.render(tdata))
-      placeholders[module_name][placeholder_name].append((item, tdata))
+      # TODO(http://crbug.com/593198): enable this assert when all recipes and
+      # recipe modules are updated.
+      #assert item.id not in placeholders[module_name][placeholder_name], (
+      #    'You have multiple place holders of %s.%s, please specify different '
+      #    'ids for them.' % (module_name, placeholder_name))
+      placeholders[module_name][placeholder_name][item.id] = (item, tdata)
     else:
       new_cmd.append(item)
   rendered_step['cmd'] = new_cmd
@@ -495,8 +501,14 @@ def construct_step_result(step, retcode, placeholders):
     setattr(step_result, module_name, o)
 
     for placeholder_name, items in pholders.iteritems():
-      lst = [ph.result(step_result.presentation, td) for ph, td in items]
-      setattr(o, placeholder_name+"_all", lst)
+      named_results = {}
+      lst = []
+      for _, (ph, td) in items.iteritems():
+        result = ph.result(step_result.presentation, td)
+        lst.append(result)
+        named_results[ph.id] = result
+      setattr(o, placeholder_name + "s", named_results)
+      setattr(o, placeholder_name + "_all", lst)

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

so, actually, because of the way the recipe pinning works, you don't need to
support both:
  * prepare this CL to be the new world (e.g. foos instead of foo_all)
  * simulate it's roll into build and build_internal (I can show you how this is
done, I don't have a great document to point you at right now)
  * prepare CLs for build and build_internal as the result of that simulation
(i.e. rewrite them to use foos instead of foo_all), we'll +1 those
  * we'll +1 this
  * land this
  * update the downstream CLs to include the committed version of this in their
recipe.cfg pins
  * land the downstream CLs

We have a bug on file to automate the majority of this process, but we've done
this manually 1-2 times now and it works pretty well. It allows you to see the
full effect of the change downstream, and doesn't leave you in a weird
intermediate state where both interfaces are supported.

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

Sounds good. Let's go with this approach then.

       setattr(o, placeholder_name, lst[0])
 
   # Placeholders that are used with IO redirection.