Minor loader improvements.

recipe_engine/loader.py

 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 import collections
 import imp
 import inspect
 import os
 import sys
 
 from . import env
 
 from .config import ConfigContext, ConfigGroupSchema
 from .config_types import Path, ModuleBasePath, PackageRepoBasePath
 from .config_types import RecipeScriptBasePath
 from .config_types import RECIPE_MODULE_PREFIX
-from .recipe_api import RecipeApiPlain, RecipeScriptApi
+from .recipe_api import RecipeApi, RecipeApiPlain, RecipeScriptApi
 from .recipe_api import _UnresolvedRequirement
 from .recipe_api import BoundProperty
 from .recipe_api import UndefinedPropertyException, PROPERTY_SENTINEL
 from .recipe_test_api import RecipeTestApi, DisabledTestData
 
 
 class LoaderError(Exception):
   """Raised when something goes wrong loading recipes or modules."""
 
 
+class MalformedRecipeError(LoaderError):
+  """Raised when a recipe doesn't conform to the expected interface."""
+
+
 class NoSuchRecipe(LoaderError):
   """Raised by load_recipe is recipe is not found."""
   def __init__(self, recipe):
     super(NoSuchRecipe, self).__init__('No such recipe: %s' % recipe)
 
 
 class RecipeScript(object):
   """Holds dict of an evaluated recipe script."""
 
   def __init__(self, name, recipe_globals, package_name, path):
     self._path = path
     self._name = name
     self._recipe_globals = recipe_globals
 
     self.run_steps, self.gen_tests = [
         recipe_globals.get(k) for k in ('RunSteps', 'GenTests')]
 
+    if not self.run_steps:
+      raise MalformedRecipeError('Missing or misspelled RunSteps function.')
+
+    if not self.gen_tests:
+      raise MalformedRecipeError('Missing or misspelled GenTests function.')
+
     # Let each property object know about the property name.
     full_decl_name = '%s::%s' % (package_name, name)
     recipe_globals['PROPERTIES'] = {
         name: value.bind(
           name, BoundProperty.RECIPE_PROPERTY, full_decl_name)
         for name, value in recipe_globals.get('PROPERTIES', {}).items()}
 
     return_schema = recipe_globals.get('RETURN_SCHEMA')
     if return_schema and not isinstance(return_schema, ConfigGroupSchema):
-      raise ValueError('Invalid RETURN_SCHEMA; must be an instance of '
-                       'ConfigGroupSchema')
+      raise MalformedRecipeError(
+        'Invalid RETURN_SCHEMA; must be an instance of ConfigGroupSchema')
+
 
   @property
   def path(self):
     return self._path
 
   @property
   def name(self):
     return self._name
 
   @property
@@ skipping 381 matching lines @@
         assert not submod.CONFIG_CTX, (
           'More than one configuration context: %s, %s' %
           (submod.config, submod.CONFIG_CTX))
         submod.CONFIG_CTX = v
     assert submod.CONFIG_CTX, 'Config file, but no config context?'
 
   # Identify the RecipeApiPlain subclass as this module's API.
   submod.API = getattr(submod, 'API', None)
   assert hasattr(submod, 'api'), '%s is missing api.py' % (name,)
   for v in submod.api.__dict__.itervalues():
+    # If the recipe has literally imported the RecipeApi, we don't wan't
+    # to consider that to be the real RecipeApi :)
+    if v is RecipeApiPlain or v is RecipeApi:
+      continue
     if inspect.isclass(v) and issubclass(v, RecipeApiPlain):
       assert not submod.API, (
         '%s has more than one RecipeApi subclass: %s, %s' % (
             name, v, submod.API))
       submod.API = v
   assert submod.API, 'Submodule has no api? %s' % (submod)
 
   # Identify the (optional) RecipeTestApi subclass as this module's test API.
   submod.TEST_API = getattr(submod, 'TEST_API', None)
   if hasattr(submod, 'test_api'):
     for v in submod.test_api.__dict__.itervalues():
+      # If the recipe has literally imported the RecipeTestApi, we don't wan't
+      # to consider that to be the real RecipeTestApi :)
+      if v is RecipeTestApi:
+        continue
       if inspect.isclass(v) and issubclass(v, RecipeTestApi):
         assert not submod.TEST_API, (
           'More than one TestApi subclass: %s' % submod.api)
         submod.TEST_API = v
     assert submod.API, (
       'Submodule has test_api.py but no TestApi subclass? %s'
       % (submod)
     )
 
   # Let each property object know about the property name.
@@ skipping 200 matching lines @@
   for k,v in toplevel_deps.iteritems():
     setattr(api, k, mapper.instantiate(v))
   return api
 
 
 def _resolve_requirement(req, engine):
   if req._typ == 'client':
     return engine._get_client(req._name)
   else:
     raise ValueError('Unknown requirement type [%s]' % (req._typ,))