morphologyfactory: move empty stratum check here

It is better to test whether a straum is empty here, since it will be
noticed earlier in the build, as soon as the morphologies are loaded,
rather than after they have all been parsed.

It is also conceptually nicer to put it here, since the morphologyfactory
was written to perform this kind of validation.

On a more practical note, the validation is moved here so that the test
for this error isn't masked by the test for no build dependencies.

To ensure tests still pass, we alter the stratum morphology used by
other unit tests to no longer be empty, and add an empty one to test.

3 files changed, 28 insertions, 10 deletions

diff --git a/morphlib/builder2.py b/morphlib/builder2.py
index daf50b56..e1eaaa86 100644
--- a/morphlib/builder2.py
+++ b/morphlib/builder2.py
@@ -469,8 +469,6 @@ class StratumBuilder(BuilderBase):
         with self.build_watch('overall-build'):
             constituents = [d for d in self.artifact.dependencies
                             if self.is_constituent(d)]
-            if len(constituents) == 0:
-                raise EmptyStratumError(self.artifact.name)
 
             # the only reason the StratumBuilder has to download chunks is to
             # check for overlap now that strata are lists of chunks
@@ -707,10 +705,3 @@ class Builder(object):  # pragma: no cover
         built_artifacts = o.build_and_cache()
         logging.debug('Builder.build: done')
         return built_artifacts
-
-
-class EmptyStratumError(cliapp.AppException):
-
-    def __init__(self, stratum_name): # pragma: no cover
-        cliapp.AppException.__init__(self,
-            "Stratum %s is empty (has no dependencies)" % stratum_name)
diff --git a/morphlib/morphologyfactory.py b/morphlib/morphologyfactory.py
index 394d186a..fa71e820 100644
--- a/morphlib/morphologyfactory.py
+++ b/morphlib/morphologyfactory.py
@@ -47,6 +47,13 @@ class NoChunkBuildDependsError(StratumError):
                   '(build-depends is a mandatory field)' % (stratum, chunk))
 
 
+class EmptyStratumError(StratumError):
+
+    def __init__(self, stratum):
+        cliapp.AppException.__init__(self,
+            "Stratum %s is empty (has no dependencies)" % stratum)
+
+
 class MorphologyFactory(object):
 
     '''An way of creating morphologies which will provide a default'''
@@ -147,6 +154,9 @@ class MorphologyFactory(object):
     def _check_and_tweak_stratum(self, morphology, reponame, sha1, filename):
         '''Check and tweak a stratum morphology.'''
 
+        if len(morphology['chunks']) == 0:
+            raise EmptyStratumError(morphology['name'])
+
         for source in morphology['chunks']:
             if source.get('build-depends', None) is None:
                 name = source.get('name', source.get('repo', 'unknown'))
diff --git a/morphlib/morphologyfactory_tests.py b/morphlib/morphologyfactory_tests.py
index 7a3dc343..de1be017 100644
--- a/morphlib/morphologyfactory_tests.py
+++ b/morphlib/morphologyfactory_tests.py
@@ -57,7 +57,15 @@ class FakeLocalRepo(object):
             }''',
         'stratum.morph': '''{
                 "name": "stratum",
-                "kind": "stratum"
+                "kind": "stratum",
+                "chunks": [
+                    {
+                        "name": "chunk",
+                        "repo": "test:repo",
+                        "ref": "sha1",
+                        "build-depends": []
+                    }
+                ]
             }''',
         'stratum-no-chunk-bdeps.morph': '''{
                 "name": "stratum-no-chunk-bdeps",
@@ -71,6 +79,10 @@ class FakeLocalRepo(object):
                     }
                 ]
             }''',
+        'stratum-empty.morph': '''{
+                "name": "stratum-empty",
+                "kind": "stratum"
+            }''',
         'system.morph': '''{
                 "name": "system",
                 "kind": "system",
@@ -278,3 +290,8 @@ class MorphologyFactoryTests(unittest.TestCase):
                           self.mf.get_morphology, 'reponame', 'sha1',
                           'stratum-no-chunk-bdeps.morph')
 
+    def test_fails_on_empty_stratum(self):
+        self.assertRaises(
+            morphlib.morphologyfactory.EmptyStratumError,
+            self.mf.get_morphology, 'reponame', 'sha1', 'stratum-empty.morph')
+