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 ae127e99692fabda3d9545dc8ff4cd0eaac94dc0..bfa10f6eee24e527a58554ed3046f6f1f36efe5f 100644
--- a/recipe_engine/step_runner.py
+++ b/recipe_engine/step_runner.py
@@ -449,19 +449,26 @@ def render_step(step, step_test):
 
   # Process 'cmd', rendering placeholders there.
   input_phs = collections.defaultdict(lambda: collections.defaultdict(list))
-  output_phs = collections.defaultdict(lambda: collections.defaultdict(list))
+  output_phs = 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
+      module_name, placeholder_name = item.namespaces
       if isinstance(item, util.InputPlaceholder):
-        tdata = step_test.pop_input_placeholder(item.name_pieces)
+        tdata = step_test.pop_input_placeholder(module_name, placeholder_name)
         input_phs[module_name][placeholder_name].append((item, tdata))
       else:
         assert isinstance(item, util.OutputPlaceholder), (
             'Not an OutputPlaceholder: %r' % item)
-        tdata = step_test.pop_output_placeholder(item.name_pieces)
-        output_phs[module_name][placeholder_name].append((item, tdata))
+        # This assert also ensures at most one placeholder has the default name.
+        assert item.name not in output_phs[module_name][placeholder_name], (
+            'Step "%s" has multiple output placeholders of %s.%s. Please '
+            'specify explicit and different names for them.' % (
+              step['name'], module_name, placeholder_name))
+        tdata = step_test.pop_output_placeholder(
+            module_name, placeholder_name, item.name)
+        output_phs[module_name][placeholder_name][item.name] = (item, tdata)
       new_cmd.extend(item.render(tdata))
     else:
       new_cmd.append(item)
@@ -512,10 +519,22 @@ def construct_step_result(step, retcode, placeholders):
     o = BlankObject()
     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)
-      setattr(o, placeholder_name, lst[0])
+    for placeholder_name, instances in pholders.iteritems():
+      named_results = {}
+      for _, (ph, td) in instances.iteritems():
+        named_results[ph.name] = ph.result(step_result.presentation, td)
+      setattr(o, placeholder_name + "s", named_results)
+
+      default_result = None
+      if len(named_results) == 1:  # Only 1 output placeholder.
+        default_result = named_results.values()[0]
+      else:
+        # 2+ output placeholder, check for the one without an explicit name.
+        for ph, _ in instances.values():
+          if ph.name is None:
+            default_result = named_results[ph.name]
+            break
+      setattr(o, placeholder_name, default_result)
 
   # Placeholders that are used with IO redirection.
   for key in ('stdout', 'stderr', 'stdin'):