Handle uninitialized submodule and commit streams

<!-- agent -->
RootModule.update could swallow setup failures with keep_going and then
iterate sms before assignment. Start with an empty submodule list so the
handled failure safely skips updates.

Commit iteration could likewise read stream before assignment for processes
without stdout or unsupported inputs. Raise explicit input errors instead.

Assisted-by: GPT 5.6
Co-authored-by: GPT 5.6 <codex@openai.com>

Author: Byron

git/objects/commit.py

@@ -575,11 +575,14 @@ def _iter_from_process_or_stream(cls, repo: "Repo", proc_or_stream: Union[Popen,
 
         if hasattr(proc_or_stream, "wait"):
             proc_or_stream = cast(Popen, proc_or_stream)
-            if proc_or_stream.stdout is not None:
-                stream = proc_or_stream.stdout
+            stream = proc_or_stream.stdout
+            if stream is None:
+                raise ValueError("Process has no stdout stream")
         elif hasattr(proc_or_stream, "readline"):
             proc_or_stream = cast(IO, proc_or_stream)  # type: ignore[redundant-cast]
             stream = proc_or_stream
+        else:
+            raise TypeError("Expected a process or stream")
 
         readline = stream.readline
         while True:

git/objects/submodule/root.py

@@ -7,6 +7,7 @@
 
 import git
 from git.exc import InvalidGitRepositoryError
+from git.util import IterableList
 
 from .base import Submodule, UpdateProgress
 from .util import find_first_remote_branch
@@ -19,7 +20,6 @@
 
 if TYPE_CHECKING:
     from git.repo import Repo
-    from git.util import IterableList
 
 # ----------------------------------------------------------------------------
 
@@ -162,6 +162,7 @@ def update(  # type: ignore[override]
             prefix = "DRY-RUN: "
 
         repo = self.repo
+        sms: "IterableList[Submodule]" = IterableList("name")
 
         try:
             # SETUP BASE COMMIT
@@ -182,7 +183,7 @@ def update(  # type: ignore[override]
             # END handle previous commit
 
             psms: "IterableList[Submodule]" = self.list_items(repo, parent_commit=previous_commit)
-            sms: "IterableList[Submodule]" = self.list_items(repo)
+            sms = self.list_items(repo)
             spsms = set(psms)
             ssms = set(sms)
 

test/test_commit.py

@@ -327,6 +327,11 @@ def test_rev_list_bisect_all(self):
         for sha1, commit in zip(expected_ids, commits):
             self.assertEqual(sha1, commit.hexsha)
 
+    def test_iter_from_invalid_process_or_stream(self):
+        for source, error in ((Mock(wait=Mock(), stdout=None), ValueError), (object(), TypeError)):
+            with self.assertRaises(error):
+                list(Commit._iter_from_process_or_stream(self.rorepo, source))
+
     @with_rw_directory
     def test_ambiguous_arg_iteration(self, rw_dir):
         rw_repo = Repo.init(osp.join(rw_dir, "test_ambiguous_arg"))

test/test_submodule.py

@@ -511,6 +511,9 @@ def test_root_module(self, rwrepo):
         # Cannot set the parent commit as root module's path didn't exist.
         self.assertRaises(ValueError, rm.set_parent_commit, "HEAD")
 
+        with mock.patch.object(RootModule, "list_items", side_effect=ValueError("boom")):
+            rm.update(keep_going=True)
+
         # TEST UPDATE
         #############
         # Set up a commit that removes existing, adds new and modifies existing