Re: [PATCH] remote: make prune work for mixed mirror/non-mirror repos

On Thu, Jun 20, 2013 at 03:46:20PM -0700, Junio C Hamano wrote:

Dennis Kaarsemaker [off-list ref] writes:

quoted

When cloning a repo with --mirror, and adding more remotes later,
get_stale_heads for origin would mark all refs from other repos as stale. In
this situation, with refs-src and refs->dst both equal to refs/*, we should
ignore refs/remotes/* when looking for stale refs to prevent this from
happening.

I do not think it is a right solution to single out refs/remotes/*.

Yeah, I agree.

Going back to your original example:

    [remote "origin"]
            url = git://github.com/git/git.git
            fetch = +refs/*:refs/*
            mirror = true
    [remote "peff"]
            url = git://github.com/peff/git.git
            fetch = +refs/heads/*:refs/remotes/peff/*

There is a fundamental namespace conflict here: one remote is claiming
the whole refs/* namespace, and another remote is claiming some subset.
"fetch --prune" is only one type of problem you can have; you might also
overwrite stuff from the "peff" remote with stuff from the "origin"
remote (if it happens to have "refs/remotes/peff/foo" itself).

I think this is an unsolvable problem, and I _think_ the root cause
of the issue is the configuration above that allows the RHS of
different fetch refspecs to overlap.  refs/* is more generic and
covers refs/remotes/peff/* and refs/remotes/github/*.  You cannot
even know, just by looking at "origin" and your local repository,
if refs/remotes/github/html you have should go away or it might have
come from somewhere else.

Exactly.

The best we _could_ do, without contacting all the defined remotes,
is probably to check each ref that we did not see from "origin" (for
example, you find "refs/remotes/peff/frotz" that your origin does
not have) and see if it could match RHS of fetch refspec of somebody
else (e.g. RHS of "refs/heads/*:refs/remotes/peff/*" matches that
ref).  Then we can conclude that refs/remotes/peff/frotz _might_
have come from Peff's repository and not from "origin", and then we
can optionally issue a warning and refrain from removing it.

I think this is just papering over the problem in one instance. What
happens when you _do_ have overlapping refs in the "origin" remote, and
you have a true conflict.

I wonder why Dennis wants to "refs/*:refs/*" in the first place. It
is not usually a useful thing to have in a non-bare repository, because
fetches will overwrite local work on branches. If he just wanted the
automatic "git push --mirror" setting, that does not depend on the fetch
refspec.

We made this distinction in "git remote --mirror={fetch,remote}", but I
don't think "git clone --mirror" ever learned about it.

-Peff