[step_runner] run _merge_envs in simulation too.

recipe_modules/context/api.py

Index: recipe_modules/context/api.py
diff --git a/recipe_modules/context/api.py b/recipe_modules/context/api.py
index de7075670061fff5f591ada696c4515c01121531..33556301a8b156b43ce092068f5f8fa7a9acfbfe 100644
--- a/recipe_modules/context/api.py
+++ b/recipe_modules/context/api.py
@@ -25,6 +25,7 @@ Example:
 """
 
 
+import collections
 import copy
 
 from contextlib import contextmanager
@@ -137,8 +138,18 @@ class ContextApi(RecipeApi):
       check_type('env', env, dict)
       # strify everything except None in the env to allow for ints, Paths, etc.
       # None has special meaning (i.e. "delete this env key")
-      kwargs['env'] = {str(k): (str(v) if v is not None else None)
-                       for k, v in env.iteritems()}
+      new_env = {}
+      for k, v in env.iteritems():
+        k = str(k)
+        if v is not None:
+          v = str(v)
+          try:
+            v % collections.defaultdict(str)

[nodir, 2017/05/31 21:49:03]

it does not fail for v==`%s'

[iannucci, 2017/05/31 22:07:55]

Done.

+          except Exception:
+            raise ValueError(('Invalid %%-formatting parameter in envvar, '
+                              'only %%(ENVVAR)s allowed: %r') % (v,))
+        new_env[k] = v
+      kwargs['env'] = new_env
 
     if not kwargs:
       yield