Re: linux-next: unnecessary merge in the v4l-dvb tree
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Feb 14, 2018, 18:12 UTC
- Message-ID
- <xmqqfu63o2xv.fsf@gitster-ct.c.googlers.com>
- In-Reply-To
- <CA+55aFxkYTeY9h=VHFXi=gbXsnsHCRMAVZ9=1_EsFGSqr0sj9g@mail.gmail.com>
Linus Torvalds <torvalds@linux-foundation.org> writes:
Show 23 quoted lines
> On Tue, Feb 13, 2018 at 9:18 AM, Junio C Hamano <gitster@pobox.com> wrote:
>>
>> That makes me wonder if another heuristic I floated earlier is more
>> appropriate. When merging a tag object T, if refs/tags/T exists and
>> it is that tag object, then an updated "merge" would default to "--ff";
>> otherwise, it would keep the current default of creating a merge even
>> when we could fast-forward, in order to record that tag T in the
>> resulting history.
>
> Oooh. Yes, that sounds like the right thing to do.
>
> So the "no fast-forward" logic would trigger only if the name we used
> for merging is one of the temporary ones (ie .git/{FETCH,MERGE}_HEAD),
> not if the mentioned tag is already a normal tag reference.
>
> Then it's very explicitly about "don't lose the signing information".
>
> I'd still have to teach people to use "--only-ff" if they don't do the
> "fetch and merge" model but literally just do "git pull upstream
> vX.Y", but at least the case Mauro describes would automatically just
> DTRT.
>
> Me likey.The implementation cannot exactly be "did the user give FETCH_HEAD or v4.16-rc1 from the command line?", because we'd want to catch it when Mauro says "git fetch linus && git merge v4.16-rc1" and behave identically as "git pull linus v4.16-rc1" (and the latter internally gets turned into "git merge FETCH_HEAD").
So, instead, we read the "tag" line from the tag object to learn the tagname T, see if refs/tags/T exists and points at that object, to see if we are Mauro who follows your tags, or if we are you who fetch and merge contributors' "for-linus" signed tag (which I am assuming you won't contaminate your refs/tags/ hierarchy with).
There are a few fallouts in the testsuite if we go this route. I am not quite decided if I like the approach.
builtin/merge.c | 42 ++++++++++++++++++++++++++++++++++++++---- t/t6200-fmt-merge-msg.sh | 2 +- t/t7600-merge.sh | 2 +- 3 files changed, 40 insertions(+), 6 deletions(-)
diff --git a/builtin/merge.c b/builtin/merge.c index 30264cfd7c..45c7916505 100644 --- a/builtin/merge.c +++ b/builtin/merge.c @@ -33,6 +33,7 @@ #include "sequencer.h" #include "string-list.h" #include "packfile.h" +#include "tag.h" #define DEFAULT_TWOHEAD (1<<0) #define DEFAULT_OCTOPUS (1<<1) @@ -1125,6 +1126,42 @@ static struct commit_list *collect_parents(struct commit *head_commit, return remoteheads; } +static int merging_a_throwaway_tag(struct commit *commit) +{ + const char *tag_ref; + struct object_id oid; + + /* Are we merging a tag? */ + if (!merge_remote_util(commit) || + !merge_remote_util(commit)->obj || + merge_remote_util(commit)->obj->type != OBJ_TAG) + return 0; + + /* + * Now we know we are merging a tag object. Are we downstream + * and following the tags from upstream? If so, we must have + * the tag object pointed at by "refs/tags/$T" where $T is the + * tagname recorded in the tag object. We want to allow such + * a "just to catch up" merge to fast-forward. + */ + tag_ref = xstrfmt("refs/tags/%s", + ((struct tag *)merge_remote_util(commit)->obj)->tag); + + if (!read_ref(tag_ref, &oid) && + !oidcmp(&oid, &merge_remote_util(commit)->obj->oid)) + return 0; + + /* + * Otherwise, we are playing an integrator's role, making a + * merge with a throw-away tag from a contributor with + * something like "git pull $contributor $signed_tag". + * We want to forbid such a merge from fast-forwarding + * by default; otherwise we would not keep the signature + * anywhere. + */ + return 1; +} + int cmd_merge(int argc, const char **argv, const char *prefix) { struct object_id result_tree, stash, head_oid; @@ -1322,10 +1359,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix) oid_to_hex(&commit->object.oid)); setenv(buf.buf, merge_remote_util(commit)->name, 1); strbuf_reset(&buf); - if (fast_forward != FF_ONLY && - merge_remote_util(commit) && - merge_remote_util(commit)->obj && - merge_remote_util(commit)->obj->type == OBJ_TAG) + if (fast_forward != FF_ONLY && merging_a_throwaway_tag(commit)) fast_forward = FF_NO; } diff --git a/t/t6200-fmt-merge-msg.sh b/t/t6200-fmt-merge-msg.sh index 2e2fb0e957..a54a52aaa4 100755 --- a/t/t6200-fmt-merge-msg.sh +++ b/t/t6200-fmt-merge-msg.sh @@ -512,7 +512,7 @@ test_expect_success 'merge-msg with "merging" an annotated tag' ' test_when_finished "git reset --hard" && annote=$(git rev-parse annote) && - git merge --no-commit $annote && + git merge --no-commit --no-ff $annote && { cat <<-EOF Merge tag '\''$annote'\'' diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh index dfde6a675a..28a1c43ca7 100755 --- a/t/t7600-merge.sh +++ b/t/t7600-merge.sh @@ -718,7 +718,7 @@ test_expect_success GPG 'merge --no-edit tag should skip editor' ' git tag -f -s -m "A newer commit" signed && git reset --hard c0 && - EDITOR=false git merge --no-edit signed && + EDITOR=false git merge --no-edit --no-ff signed && git rev-parse signed^0 >expect && git rev-parse HEAD^2 >actual && test_cmp expect actual