Patch update for more robust behavior with adjusted branches

changelog.d/20231025_202631_michael.hanke_bf_core_7522.md

@@ -0,0 +1,6 @@
+### 🐛 Bug Fixes
+
+- Add patch to fix `update`'s target detection for adjusted mode datasets
+  that can crash under some circumstances.
+  See https://github.com/datalad/datalad/issues/7507, fixed via
+  https://github.com/datalad/datalad-next/pull/509 (by @mih)

datalad_next/patches/enabled.py

@@ -13,4 +13,5 @@
     customremotes_main,
     create_sibling_gitlab,
     run,
+    update,
 )

datalad_next/patches/update.py

@@ -0,0 +1,58 @@
+"""Robustify ``update()`` target detection for adjusted mode datasets
+
+The true cause of the problem is not well understood.
+https://github.com/datalad/datalad/issues/7507 documents that it is not
+easy to capture the breakage in a test.
+"""
+
+from . import apply_patch
+
+
+# This function is taken from datalad-core@cdc0ceb30ae04265c5369186acf2ab2683a8ec96
+# datalad/distribution/update.py
+# The change has been proposed in https://github.com/datalad/datalad/pull/7522
+def _choose_update_target(repo, branch, remote, cfg_remote):
+    """Select a target to update `repo` from.
+
+    Note: This function is not concerned with _how_ the update is done (e.g.,
+    merge, reset, ...).
+
+    Parameters
+    ----------
+    repo : Repo instance
+    branch : str
+        The current branch.
+    remote : str
+        The remote which updates are coming from.
+    cfg_remote : str
+        The configured upstream remote.
+
+    Returns
+    -------
+    str (the target) or None if a choice wasn't made.
+    """
+    target = None
+    if cfg_remote and remote == cfg_remote:
+        # Use the configured cfg_remote branch as the target.
+        #
+        # In this scenario, it's tempting to use FETCH_HEAD as the target. For
+        # a merge, that would be the equivalent of 'git pull REMOTE'. But doing
+        # so would be problematic when the GitRepo.fetch() call was passed
+        # all_=True. Given we can't use FETCH_HEAD, it's tempting to use the
+        # branch.*.merge value, but that assumes a value for remote.*.fetch.
+        target = repo.call_git_oneline(
+            ["rev-parse", "--symbolic-full-name", "--abbrev-ref=strict",
+             # THIS IS THE PATCH: prefix @{upstream} with the branch name
+             # of the corresponding branch
+             f"{repo.get_corresponding_branch(branch) or ''}" "@{upstream}"],
+            read_only=True)
+    elif branch:
+        remote_branch = "{}/{}".format(remote, branch)
+        if repo.commit_exists(remote_branch):
+            target = remote_branch
+    return target
+
+
+apply_patch(
+    'datalad.distribution.update', None, '_choose_update_target',
+    _choose_update_target)