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sequencer: fast-forward `merge` commands, if possible 

Just like with regular `pick` commands, if we are trying to rebase a
merge commit, we now test whether the parents of said commit match HEAD
and the commits to be merged, and fast-forward if possible.

This is not only faster, but also avoids unnecessary proliferation of
new objects.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Johannes Schindelin 2018-04-25 14:28:56 +02:00 committed by Junio C Hamano
parent 4c68e7ddb5
commit d1e8b0114b
1 changed files with 32 additions and 1 deletions
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33
sequencer.c
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@ -2687,7 +2687,7 @@ static int do_merge(struct commit *commit, const char *arg, int arg_len,
struct commit *head_commit, *merge_commit, *i;
struct commit_list *bases, *j, *reversed = NULL;
struct merge_options o;
int merge_arg_len, oneline_offset, ret;
int merge_arg_len, oneline_offset, can_fast_forward, ret;
static struct lock_file lock;
const char *p;
@ -2772,6 +2772,37 @@ static int do_merge(struct commit *commit, const char *arg, int arg_len,
}
}
/*
* If HEAD is not identical to the first parent of the original merge
* commit, we cannot fast-forward.
*/
can_fast_forward = opts->allow_ff && commit && commit->parents &&
!oidcmp(&commit->parents->item->object.oid,
&head_commit->object.oid);
/*
* If the merge head is different from the original one, we cannot
* fast-forward.
*/
if (can_fast_forward) {
struct commit_list *second_parent = commit->parents->next;
if (second_parent && !second_parent->next &&
oidcmp(&merge_commit->object.oid,
&second_parent->item->object.oid))
can_fast_forward = 0;
}
if (can_fast_forward && commit->parents->next &&
!commit->parents->next->next &&
!oidcmp(&commit->parents->next->item->object.oid,
&merge_commit->object.oid)) {
rollback_lock_file(&lock);
ret = fast_forward_to(&commit->object.oid,
&head_commit->object.oid, 0, opts);
goto leave_merge;
}
write_message(oid_to_hex(&merge_commit->object.oid), GIT_SHA1_HEXSZ,
git_path_merge_head(), 0);
write_message("no-ff", 5, git_path_merge_mode(), 0);