[PATCH 2/2] patch-ids: skip merge commits
- From
Jeff King <peff@peff.net>
- Date
- Sep 7, 2016, 07:54 UTC
- Message-ID
- <20160907075425.6jgamuwm66xbklu3@sigill.intra.peff.net>
- In-Reply-To
- <20160907075346.z6wtmqnfc6bsunjb@sigill.intra.peff.net>
The patch-ids code which powers "log --cherry-pick" doesn't look at whether each commit is a merge or not. It just feeds the commit's first parent to the diff, and ignores any additional parents.
In theory, this might be useful if you wanted to find equivalence between, say, a merge commit and a squash-merge that does the same thing. But that may also be the wrong thing; the diffs may be the same, but the meaning of the two commits is definitely not identical. We should err on the side of _not_ matching such commits.
Moreover, we may spend a lot of extra time computing these merge diffs. In the case that inspired this patch, a "git format-patch --cherry-pick" dropped from over 3 minutes to less than 4 seconds. This seems pretty drastic, but is easily explained. The command was invoked by a "git rebase" of an older topic branch; there had been tens of thousands of commits on the upstream branch in the meantime. In addition, this project used a topic-branch workflow with occasional "back-merges" from "master" to each topic (to resolve conflicts on the topics rather than in the merge commits). So there were not only extra merges, but the diffs for these back-merges were generally quite large (because they represented _everything_ that had been merged to master since the topic branched).
This patch just ignores merge commits entirely when generating patch-ids, meaning they will never be matched (from either side of a symmetric-diff traversal).
Signed-off-by: Jeff King <peff@peff.net> --- patch-ids.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/patch-ids.c b/patch-ids.c index 77e4663..b1f8514 100644 --- a/patch-ids.c +++ b/patch-ids.c @@ -7,10 +7,12 @@ int commit_patch_id(struct commit *commit, struct diff_options *options, unsigned char *sha1, int diff_header_only) { - if (commit->parents) + if (commit->parents) { + if (commit->parents->next) + return 0; diff_tree_sha1(commit->parents->item->object.oid.hash, commit->object.oid.hash, "", options); - else + } else diff_root_tree_sha1(commit->object.oid.hash, "", options); diffcore_std(options); return diff_flush_patch_id(options, sha1, diff_header_only);
-- 2.10.0.rc2.154.gb4a4b8b