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>
Johannes Schindelin committed
Apr 25, 2018 at 14:28 UTC
d1e8b0114bef98e8efe3f8d35430300ff9e00443
1 file changed
+32
-1
sequencer.c
+32
-1
@@ -2687,7 +2687,7 @@ static int do_merge(struct commit *commit, const char *arg, int arg_len,
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struct commit *head_commit, *merge_commit, *i;
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struct commit_list *bases, *j, *reversed = NULL;
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struct merge_options o;
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- int merge_arg_len, oneline_offset, ret;
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+ int merge_arg_len, oneline_offset, can_fast_forward, ret;
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static struct lock_file lock;
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const char *p;
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@@ -2772,6 +2772,37 @@ static int do_merge(struct commit *commit, const char *arg, int arg_len,
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}
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}
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+ /*
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+ * If HEAD is not identical to the first parent of the original merge
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+ * commit, we cannot fast-forward.
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+ */
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+ can_fast_forward = opts->allow_ff && commit && commit->parents &&
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+ !oidcmp(&commit->parents->item->object.oid,
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+ &head_commit->object.oid);
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+
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+ /*
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+ * If the merge head is different from the original one, we cannot
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+ * fast-forward.
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+ */
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+ if (can_fast_forward) {
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+ struct commit_list *second_parent = commit->parents->next;
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+
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+ if (second_parent && !second_parent->next &&
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+ oidcmp(&merge_commit->object.oid,
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+ &second_parent->item->object.oid))
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+ can_fast_forward = 0;
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+ }
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+
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+ if (can_fast_forward && commit->parents->next &&
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+ !commit->parents->next->next &&
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+ !oidcmp(&commit->parents->next->item->object.oid,
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+ &merge_commit->object.oid)) {
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+ rollback_lock_file(&lock);
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+ ret = fast_forward_to(&commit->object.oid,
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+ &head_commit->object.oid, 0, opts);
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+ goto leave_merge;
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+ }
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+
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write_message(oid_to_hex(&merge_commit->object.oid), GIT_SHA1_HEXSZ,
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git_path_merge_head(), 0);
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write_message("no-ff", 5, git_path_merge_mode(), 0);