input: introduce failUnstableCheckouts policy

We are about to fail unstable checkouts of deterministic recipes. Some
old projects could rely on the previous behaviour to transparently
handle such situations, though.

Author: jkloetzke

pym/bob/input.py

@@ -3160,6 +3160,7 @@ class RecipeSet:
                 schema.Optional('substituteMetaEnv') : bool,
                 schema.Optional('managedLayers') : bool,
                 schema.Optional('urlScmSeparateDownload') : bool,
+                schema.Optional('failUnstableCheckouts') : bool,
             },
             error="Invalid policy specified! Are you using an appropriate version of Bob?"
         ),
@@ -3218,7 +3219,12 @@ class RecipeSet:
             "0.25.1.dev27",
             InfoOnce("urlScmSeparateDownload policy is not set. Extracted archives of the 'url' SCM are retained in the workspace.",
                 help="See http://bob-build-tool.readthedocs.io/en/latest/manual/policies.html#urlscmseparatedownload for more information.")
-        )
+        ),
+        "failUnstableCheckouts" : (
+            "0.25.1.dev88",
+            InfoOnce("failUnstableCheckouts policy is not set. Unexpected indeterministic checkouts are not flagged as error.",
+                help="See http://bob-build-tool.readthedocs.io/en/latest/manual/policies.html#failunstablecheckouts for more information.")
+        ),
     }
 
     _ignoreCmdConfig = False

pym/bob/intermediate.py

@@ -554,6 +554,7 @@ def fromRecipeSet(cls, recipeSet):
             'fixImportScmVariant' : recipeSet.getPolicy('fixImportScmVariant'),
             'defaultFileMode' : recipeSet.getPolicy('defaultFileMode'),
             'urlScmSeparateDownload' : recipeSet.getPolicy('urlScmSeparateDownload'),
+            'failUnstableCheckouts' : recipeSet.getPolicy('failUnstableCheckouts'),
         }
         self.__data['archiveSpec'] = recipeSet.archiveSpec()
         self.__data['envWhiteList'] = sorted(recipeSet.envWhiteList())