On 18/01/18 15:35, Johannes Schindelin wrote:
>
> Just like with regular `pick` commands, if we are trying to recreate 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.
I might have missed something but shouldn't this be checking opts->allow_ff?
Another possible optimization is that if the parent branches have only
reworded commits or some commits that have been squashed but no other
changes then their trees will be the same as in the original merge
commit and so could be reused without calling merge_recursive().
> Signed-off-by: Johannes Schindelin <johannes.schindelin@xxxxxx>
> ---
> sequencer.c | 21 ++++++++++++++++++++-
> 1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/sequencer.c b/sequencer.c
> index 567cfcbbe8b..a96255426e7 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -2085,7 +2085,7 @@ static int do_merge(struct commit *commit, const char *arg, int arg_len,
> struct commit *head_commit, *merge_commit, *i;
> struct commit_list *common, *j, *reversed = NULL;
> struct merge_options o;
> - int ret;
> + int can_fast_forward, ret;
> static struct lock_file lock;
>
> for (merge_arg_len = 0; merge_arg_len < arg_len; merge_arg_len++)
> @@ -2151,6 +2151,14 @@ static int do_merge(struct commit *commit, const char *arg, int arg_len,
> return error(_("Cannot merge without a current revision"));
> }
>
> + /*
> + * If HEAD is not identical to the parent of the original merge commit,
> + * we cannot fast-forward.
> + */
> + can_fast_forward = commit && commit->parents &&
> + !oidcmp(&commit->parents->item->object.oid,
> + &head_commit->object.oid);
> +
> strbuf_addf(&ref_name, "refs/rewritten/%.*s", merge_arg_len, arg);
> merge_commit = lookup_commit_reference_by_name(ref_name.buf);
> if (!merge_commit) {
> @@ -2164,6 +2172,17 @@ static int do_merge(struct commit *commit, const char *arg, int arg_len,
> rollback_lock_file(&lock);
> return -1;
> }
> +
> + if (can_fast_forward && commit->parents->next &&
> + !commit->parents->next->next &&
> + !oidcmp(&commit->parents->next->item->object.oid,
> + &merge_commit->object.oid)) {
> + strbuf_release(&ref_name);
> + rollback_lock_file(&lock);
> + return fast_forward_to(&commit->object.oid,
> + &head_commit->object.oid, 0, opts);
> + }
> +
> 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);
>
