Re: Syncing HEAD

[Jeff King <peff@peff.net>]

On Tue, Aug 14, 2018 at 10:09:37PM +0200, Christian Couder wrote:

> When cloning with --mirror, the clone gets its HEAD initialized with
> the value HEAD has in its origin remote. After that if HEAD changes in
> origin there is no simple way to sync HEAD at the same time as the
> refs are synced.
> 
> It looks like the simplest way to sync HEAD is:
> 
> 1) git remote show origin
> 2) parse "HEAD branch: XXX" from the output of the above command
> 3) git symbolic-ref HEAD refs/heads/XXX

How about:

  git remote set-head origin -a

?

> It looks like it would be quite easy to add an option to `fetch` to
> sync HEAD at the same time as regular refs are synced because every
> fetch from an origin that uses a recent Git contains something like:

I think the "remote set-head" option is not very discoverable, since
people are used to working with "fetch", making it the natural place to
look. Just like we ported "remote update" over to "fetch --all", I think
it would be sensible to have "fetch --update-head" or similar.

One tricky thing is that the name "refs/remotes/<remote>/HEAD" is only
special by convention, and that convention is known on the writing side
only by git-clone and git-remote. So obviously:

  git fetch --update-head https://example.com/

is nonsense. We don't even have a ref. What should:

  git config remote.origin.fetch refs/heads/*:refs/remotes/foo/*
  git fetch --update-head origin

do? Should it update based no the remote name, or based on the refspec?
What happens if there are several refspecs? Etc.

99% of the time those questions won't come up. But we should design so
that we do the obvious thing in those 99%, and something sane in the
other 1%.

-Peff