Track step nesting in StreamEngine (Reland).

recipe_modules/step/api.py

Index: recipe_modules/step/api.py
diff --git a/recipe_modules/step/api.py b/recipe_modules/step/api.py
index b60124c1b1b4e04c08cee64985c9ca7fa15f4158..8154e2fc5888df63e0375da26e667b9f58589d90 100644
--- a/recipe_modules/step/api.py
+++ b/recipe_modules/step/api.py
@@ -13,6 +13,7 @@ class StepApi(recipe_api.RecipeApiPlain):
   def __init__(self, **kwargs):
     super(StepApi, self).__init__(**kwargs)
     self._step_names = {}
+    self._seen_steps = set()
 
   EXCEPTION = 'EXCEPTION'
   FAILURE = 'FAILURE'
@@ -135,20 +136,30 @@ class StepApi(recipe_api.RecipeApiPlain):
 
     # Obtain information from composite step parent.
     compositor = recipe_api._STEP_CONTEXT
-    name = compositor.get_with_context('name', name)
+
+    # Calculate our full step name. If a step already has that name, add an
+    # index to the end of it.
+    #
+    # Note that another step could exist with that index already added to it
+    # by the user. If this happens, we'll continue appending indexes until we
+    # have a unique step name.
+    while True:
+      full_name = compositor.get_with_context('name', name)
+      if full_name not in self._seen_steps:
+        break
+
+      step_count = self._step_names.setdefault(full_name, 1) + 1
+      self._step_names[full_name] = step_count
+      name = "%s (%d)" % (name, step_count)
+    self._seen_steps.add(full_name)
+
     if 'cwd' not in kwargs:
       kwargs['cwd'] = compositor.get('cwd')
     kwargs['env'] = compositor.get_with_context('env', kwargs.get('env', {}))
     kwargs['infra_step'] = compositor.get_with_context(
         'infra_step', bool(infra_step))
     kwargs['step_nest_level'] = compositor.get_with_context('nest_level', 0)
-
-    # Disambiguate repeated names
-    step_count = self._step_names.setdefault(name, 0) + 1
-    self._step_names[name] = step_count
-    if step_count > 1:
-      name = "%s (%d)" % (name, step_count)
-    kwargs['name'] = name
+    kwargs['name'] = full_name
 
     schema = self.make_config()
     schema.set_val(kwargs)