Better msg when gitpython fails

Currently we show a generic message.

Related: readthedocs#4371

This can be removed when gitpython-developers/GitPython#818
gets merged.

Author: stsewd

readthedocs/projects/exceptions.py

@@ -38,7 +38,11 @@ class RepositoryError(BuildEnvironmentError):
         'Private repositories are not supported.',
     )
 
-    INVALID_SUBMODULES = _('One or more submodule URLs are not valid: {}.',)
+    INVALID_SUBMODULES = _('One or more submodule URLs are not valid: {}.')
+    INVALID_SUBMODULES_PATH = _(
+        'One or more submodule paths are not valid. '
+        'Check that all your submodules in .gitmodules are used.'
+    )
 
     DUPLICATED_RESERVED_VERSIONS = _(
         'You can not have two versions with the name latest or stable.',

readthedocs/rtd_tests/tests/test_backend.py

@@ -189,6 +189,21 @@ def test_check_invalid_submodule_urls(self):
             RepositoryError.INVALID_SUBMODULES.format(['invalid']),
         )
 
+    def test_invalid_submodule_path(self):
+        repo_path = self.project.repo
+        gitmodules_path = os.path.join(repo_path, '.gitmodules')
+
+        with open(gitmodules_path, 'w+') as f:
+            content = textwrap.dedent("""
+                [submodule "not-valid-path"]
+                    path = not-valid-path
+                    url = https://github.com/readthedocs/readthedocs.org
+            """)
+            f.write(content)
+
+        with self.assertRaises(RepositoryError, msg=RepositoryError.INVALID_SUBMODULES_PATH):
+            repo.update_submodules(self.dummy_conf)
+
     @patch('readthedocs.projects.models.Project.checkout_path')
     def test_fetch_clean_tags_and_branches(self, checkout_path):
         upstream_repo = self.project.repo

readthedocs/vcs_support/backends/git.py

@@ -105,7 +105,12 @@ def validate_submodules(self, config):
         Returns the list of invalid submodules.
         """
         repo = git.Repo(self.working_dir)
-        submodules = {sub.path: sub for sub in repo.submodules}
+        try:
+            submodules = {sub.path: sub for sub in repo.submodules}
+        except InvalidGitRepositoryError:
+            raise RepositoryError(
+                RepositoryError.INVALID_SUBMODULES_PATH,
+            )
 
         for sub_path in config.submodules.exclude:
             path = sub_path.rstrip('/')