smudge filters during checkout & crash consistency

I have a case where I would like to smudge files according to the reflog information of the switching-to branch.

This is difficult to achieve because updating HEAD to the new switched-to refname or commit hash is the last step performed in a checkout prior to calling the post-checkout hook, and smudge filters process content during the rewriting of the index and work-tree before HEAD is updated.

I believe this weakness of checkout & filters also exposes a crash consistency concern. Suppose power is lost during a long-running checkout while the index/worktree is being updated but before the new HEAD file is written.

Upon coming back up, your git status will show edits against your switching-from branch, and possibilities of recovery would rely on your memory of what you were doing (instead of git-status reporting "Incomplete checkout to {branch,commit}, 'git checkout --continue' to continue").

Maybe git could record a CHECKOUT_HEAD at the start of a checkout, then at the end of the commit update_refs_for_switch() would move CHECKOUT_HEAD over top HEAD instead of rewriting HEAD (but, presumably, a lot of logic in update_refs_for_switch() would have to be relocated to when CHECKOUT_HEAD is written, other implications notwithstanding).

Crash consistency aside, my workaround for filtering will probably be to use a fake smudge filter that records the file paths of all to-be-smudged files to a file under .git/, and then use a post-commit hook that will process those files from within the newly checked-out branch (where I'll be using git-archive to overwrite files).

Seems git could fix these two concerns in one fell swoop.

Thanks,

Derek