Raise an error if a stratum build-depends on itself

If a stratum build-depends on itself, the build graph calculation
gets stuck in an infinite loop as it adds the same stratum to the
queue of morphologies to inspect over and over again.

This commit causes MorphologyLoader.validate_stratum to raise an
error if a stratum contains itself in it's build-depends, as
depending on itself makes no sense and will cause the above problem.

Change-Id: I76df5b7d63d010ae3b17f72bfa39b273e74279dd

2 files changed, 25 insertions, 0 deletions

diff --git a/morphlib/morphloader.py b/morphlib/morphloader.py
index 47cb03d7..0c69baac 100644
--- a/morphlib/morphloader.py
+++ b/morphlib/morphloader.py
@@ -195,6 +195,14 @@ class EmptySystemError(MorphologyValidationError):
             self, 'System %(system_name)s has no strata.' % locals())
 
 
+class DependsOnSelfError(MorphologyValidationError):
+
+    def __init__(self, name, filename):
+        msg = ("Stratum %(name)s build-depends on itself (%(filename)s)"
+               % locals())
+        MorphologyValidationError.__init__(self, msg)
+
+
 class MultipleValidationErrors(MorphologyValidationError):
 
     def __init__(self, name, errors):
@@ -536,6 +544,9 @@ class MorphologyLoader(object):
                 raise InvalidTypeError(
                     'build-depends', list, type(morph['build-depends']),
                     morph['name'])
+            for dep in morph['build-depends']:
+                if dep['morph'] == morph.filename:
+                    raise DependsOnSelfError(morph['name'], morph.filename)
         else:
             for spec in morph['chunks']:
                 if spec.get('build-mode') in ['bootstrap', 'test']:
diff --git a/morphlib/morphloader_tests.py b/morphlib/morphloader_tests.py
index f9fa2a34..db1872a8 100644
--- a/morphlib/morphloader_tests.py
+++ b/morphlib/morphloader_tests.py
@@ -225,6 +225,20 @@ build-system: dummy
                 morphlib.morphloader.EmptyRefError):
             self.loader.validate(m)
 
+    def test_fails_to_validate_stratum_which_build_depends_on_self(self):
+        text = '''\
+name: bad-stratum
+kind: stratum
+build-depends:
+- morph: strata/bad-stratum.morph
+chunks:
+- name: chunk
+  repo: test:repo
+  ref: foo'''
+        self.assertRaises(
+            morphlib.morphloader.DependsOnSelfError,
+            self.loader.load_from_string, text, 'strata/bad-stratum.morph')
+
     def test_fails_to_validate_system_with_obsolete_system_kind_field(self):
         m = morphlib.morphology.Morphology({
             'kind': 'system',