On 03/06/2026 11:27, Son Luong Ngoc via GitGitGadget wrote:

From: Son Luong Ngoc <redacted>

git rebase --update-refs can fail after the normal rebase path has
updated the current branch when another local branch is a symref to it.
This can happen during a default-branch rename where refs/heads/main
points at refs/heads/master while users migrate.

The sequencer queues update-ref commands from local branch decorations.
Commit 106b6885c7 (rebase: ignore non-branch update-refs) filters out
decorations that are not local branches, such as HEAD and tags. A branch
symref is different: it is still a local branch decoration, but if it
resolves to another branch then that target branch is itself present in
the decoration list and will be updated as a concrete branch.

Skip branch decorations whose symrefs resolve to refs/heads/*, because
those targets are already represented by concrete branch decorations.
This prevents aliases from scheduling a second update for the same
branch. Keep symrefs to non-branch targets on the existing path.

Makes sense

Preserve the existing checked-out branch handling before applying these
skips. Such refs still need a todo-list comment instead of an update-ref
command, even when the checked-out ref is the branch being rebased or a
branch symref alias. Use a copy of the resolved HEAD ref so later ref
resolution does not overwrite it.

I don't quite understand this. A symref that points to another branch 
should always be skipped. When we look up which branches are checked out 
(see worktree.c:add_head_info()) we use

  	refs_resolve_ref_unsafe(get_worktree_ref_store(wt),
				 "HEAD",
				 0,
				 &wt->head_oid, &flags);

so it will never report a symref as being checked out - it always 
resolves any symrefs first.

If we have a symref pointing somewhere outside of "refs/heads" then we 
need to check whether the target is checked out, not the symref itself. 
I'm not sure how likely that is to happen in practice.

This part and the test look good now

  	while (decoration) {
  		struct todo_item *item;
  		const char *path;
+		const char *resolved_ref;
+		int flags = 0;
  		size_t base_offset = ctx->buf->len;
  
  		/*
-		 * If the branch is the current HEAD, then it will be
-		 * updated by the default rebase behavior.
-		 * Exclude it from the list of refs to update,
-		 * as well as any non-branch decorations.
  		 * Non-branch decorations may be present if the pretty format
  		 * includes "%d", which would have loaded all refs
  		 * into the global decoration table.
  		 */
-		if ((head_ref && !strcmp(head_ref, decoration->name)) ||
-		    (decoration->type != DECORATION_REF_LOCAL)) {
+		if (decoration->type != DECORATION_REF_LOCAL) {
+			decoration = decoration->next;
+			continue;
+		}

If a decoration matches the current branch why don't we just skip it 
like we used to? (As an aside the existing code in wrong because if the 
user runs "git rebase --update-refs <upstream> <branch>" HEAD does not 
point to "<branch>" but lets not worry about that now)

+		path = branch_checked_out(decoration->name);

As I said above if the symref target is anther branch we should skip it 
and if the target is not a branch then we need to check if the target is 
checked out so we need to resolve the ref before calling 
branch_checked_out().

Thanks

Phillip