Re: [QUESTION] Tracking HEAD changes?

Thank you all!

I'd like to make sure I understand the way things are right now:

1. The reference-transaction hook as it's today doesn't intercept
symbolic-references changes. It means that when HEAD changes due to
branch-switching the hook won't
get called.

Are there any other cases that today the transaction won't execute? (I
couldn't think of one)

2. The mechanisms that handle the changes to index and working-dir are
isolated from the one that manages the refs updates.

A side-effect to that is the post-index-change hook running before the
reference-transaction one.
Future code changes to the way git operates could result in the
reference-transaction hook running before the post-index-change one.

Is that correct?

  Thank you!
      Yaron

On Fri, Feb 26, 2021 at 7:59 AM Jeff King [off-list ref] wrote:

On Thu, Feb 25, 2021 at 06:36:54AM +0100, Patrick Steinhardt wrote:

quoted

quoted

Hmm, I would have thought that the branch switch would trigger the hooks
because they're updating HEAD. I wonder if that is a bug (or lack of
feature :) ) in the transaction hooks, or something Patrick did
intentionally.

It was done semi-intentionally, or at least with the knowledge that
symrefs aren't covered. This is mostly because they're not covered by
the reference transaction mechanism itself.

Ah, right, I forgot about that. That might be something that we'd want
to fix if anybody wanted to use the transaction hooks to track the
complete state of refs.

At GitHub, our repository replication does track symbolic ref updates,
but we handle it outside of Git. Our normal ref updates use a few custom
bits of code similar to your transaction hooks in order to implement a
3-phase commit. But our symref updates don't; they just take a lock, run
git-symbolic-ref on each, and then vote on the result. This is slower
and less robust, but symbolic ref updates are relatively rare, so it
hasn't been a big deal.

-Peff