Better validation of project links

We should properly report errors in project links, not fail on
incomplete ones.

Closes #379

trans/tests/models.py

@@ -422,6 +422,26 @@ class SubProjectTest(RepoTestCase):
             project.full_clean
         )
 
+        # Bad link
+        project.repo = 'weblate://foo'
+        project.push = ''
+        self.assertRaisesMessage(
+            ValidationError,
+            'Invalid link to Weblate project, '
+            'use weblate://project/subproject.',
+            project.full_clean
+        )
+
+        # Bad link
+        project.repo = 'weblate://foo/bar'
+        project.push = ''
+        self.assertRaisesMessage(
+            ValidationError,
+            'Invalid link to Weblate project, '
+            'use weblate://project/subproject.',
+            project.full_clean
+        )
+
         # Translation validation
         translation = project.translation_set.get(language_code='cs')
         translation.full_clean()

trans/validators.py

@@ -85,8 +85,13 @@ def validate_repo(val):
         repo = SubProject.objects.get_linked(val)
         if repo is not None and repo.is_repo_link():
             raise ValidationError(_('Can not link to linked repository!'))
-    except SubProject.DoesNotExist:
-        raise ValidationError(_('Invalid link to repository!'))
+    except (SubProject.DoesNotExist, ValueError):
+        raise ValidationError(
+            _(
+                'Invalid link to Weblate project, '
+                'use weblate://project/subproject.'
+            )
+        )
 
 
 def validate_autoaccept(val):