Return an exception to the user if no dependency combination is determined

module_build_service/utils/submit.py

@@ -523,6 +523,9 @@ def submit_module_build(username, url, mmd, optional_params=None):
 
     validate_mmd(mmd)
     mmds = generate_expanded_mmds(db.session, mmd, raise_if_stream_ambigous, default_streams)
+    if not mmds:
+        raise ValidationError('No dependency combination was satisfied. Please verify the '
+                              'buildrequires in your modulemd have previously been built.')
     modules = []
 
     # True if all module builds are skipped so MBS will actually not rebuild

tests/test_views/test_views.py

@@ -1275,6 +1275,29 @@ class TestViews:
         assert set(dep.get_buildrequires()['platform'].get()) == expected_br
         assert set(dep.get_requires()['platform'].get()) == expected_req
 
+    @patch('module_build_service.auth.get_user', return_value=user)
+    @patch('module_build_service.scm.SCM')
+    def test_submit_build_invalid_basemodule_stream(self, mocked_scm, mocked_get_user):
+        FakeSCM(mocked_scm, 'testmodule', 'testmodule.yaml',
+                '620ec77321b2ea7b0d67d82992dda3e1d67055b4')
+
+        data = {
+            'branch': 'master',
+            'scmurl': 'https://src.stg.fedoraproject.org/modules/'
+                      'testmodule.git?#68931c90de214d9d13feefbd35246a81b6cb8d49',
+            'buildrequire_overrides': {'platform': ['28.0.0']},
+            'require_overrides': {'platform': ['f28.0.0']}
+        }
+        rv = self.client.post('/module-build-service/1/module-builds/', data=json.dumps(data))
+        result = json.loads(rv.data)
+        assert result == {
+            'error': 'Bad Request',
+            'status': 400,
+            'message': ('No dependency combination was satisfied. Please verify the '
+                        'buildrequires in your modulemd have previously been built.')
+        }
+        assert rv.status_code == 400
+
     @pytest.mark.parametrize('dep_type', ('buildrequire', 'require'))
     @patch('module_build_service.auth.get_user', return_value=user)
     @patch('module_build_service.scm.SCM')