ENH: orchestrators: Make head_at() helper abort on submodule changes

head_at() already aborts with a dirty repository to avoid losing any
changes.  But, if a submodule changed between the current and target
commit, the repository may become dirty after checking out the target.
In that case, the submodule is carrying an undefined set of changes
that could cause confusion (e.g., if the submodule change came in with
a save).

Author: kyleam

reproman/support/jobs/orchestrators.py

@@ -895,6 +895,13 @@ def head_at(dataset, commit):
         lgr.info("Checking out %s", commit)
         try:
             dataset.repo.checkout(commit)
+            # Note: It's tempting try to use --recurse-submodules here, but
+            # that will absorb submodule's .git/ directories, and DataLad
+            # relies on plain .git/ directories.
+            if dataset.repo.dirty:
+                raise OrchestratorError(
+                    "Refusing to move HEAD due to submodule state change "
+                    "within {}".format(dataset.path))
             yield moved
         finally:
             lgr.info("Restoring checkout of %s", to_restore)