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fetch: stop clobbering existing tags without --force

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Change "fetch" to treat "+" in refspecs (aka --force) to mean we
should clobber a local tag of the same name.

This changes the long-standing behavior of "fetch" added in
853a3697dc ("[PATCH] Multi-head fetch.", 2005-08-20). Before this
change, all tag fetches effectively had --force enabled. See the
git-fetch-script code in fast_forward_local() with the comment:

    > Tags need not be pointing at commits so there is no way to
    > guarantee "fast-forward" anyway.

That commit and the rest of the history of "fetch" shows that the
"+" (--force) part of refpecs was only conceived for branch updates,
while tags have accepted any changes from upstream unconditionally and
clobbered the local tag object. Changing this behavior has been
discussed as early as 2011[1].

The current behavior doesn't make sense to me, it easily results in
local tags accidentally being clobbered. We could namespace our tags
per-remote and not locally populate refs/tags/*, but as with my
97716d217c ("fetch: add a --prune-tags option and fetch.pruneTags
config", 2018-02-09) it's easier to work around the current
implementation than to fix the root cause.

So this change implements suggestion #1 from Jeff's 2011 E-Mail[1],
"fetch" now only clobbers the tag if either "+" is provided as part of
the refspec, or if "--force" is provided on the command-line.

This also makes it nicely symmetrical with how "tag" itself works when
creating tags. I.e. we refuse to clobber any existing tags unless
"--force" is supplied. Now we can refuse all such clobbering, whether
it would happen by clobbering a local tag with "tag", or by fetching
it from the remote with "fetch".

Ref updates outside refs/{tags,heads/* are still still not symmetrical
with how "git push" works, as discussed in the recently changed
pull-fetch-param.txt documentation. This change brings the two
divergent behaviors more into line with one another. I don't think
there's any reason "fetch" couldn't fully converge with the behavior
used by "push", but that's a topic for another change.

One of the tests added in 31b808a032 ("clone --single: limit the fetch
refspec to fetched branch", 2012-09-20) is being changed to use
--force where a clone would clobber a tag. This changes nothing about
the existing behavior of the test.

1. https://public-inbox.org/git/20111123221658.GA22313@sigill.intra.peff.net/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Ævar Arnfjörð Bjarmason
2018-08-31 20:10:04 +00:00
committed by Junio C Hamano
parent ae6a470334
commit 0bc8d71b99
4 changed files with 28 additions and 14 deletions
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18
builtin/fetch.c
View File

@ -664,12 +664,18 @@ static int update_local_ref(struct ref *ref,
if (!is_null_oid(&ref->old_oid) &&
starts_with(ref->name, "refs/tags/")) {
int r;
r = s_update_ref("updating tag", ref, 0);
format_display(display, r ? '!' : 't', _("[tag update]"),
r ? _("unable to update local ref") : NULL,
remote, pretty_ref, summary_width);
return r;
if (force || ref->force) {
int r;
r = s_update_ref("updating tag", ref, 0);
format_display(display, r ? '!' : 't', _("[tag update]"),
r ? _("unable to update local ref") : NULL,
remote, pretty_ref, summary_width);
return r;
} else {
format_display(display, '!', _("[rejected]"), _("would clobber existing tag"),
remote, pretty_ref, summary_width);
return 1;
}
}
current = lookup_commit_reference_gently(&ref->old_oid, 1);