From ab75a565b4c1de1bc2e94c35b118ed0ad1bdab12 Mon Sep 17 00:00:00 2001 From: Johannes Schindelin Date: Fri, 8 Nov 2024 11:35:34 +0100 Subject: [PATCH] log: --remerge-diff needs to keep around commit parents To show a remerge diff, the merge needs to be recreated. For that to work, the merge base(s) need to be found, which means that the commits' parents have to be traversed until common ancestors are found (if any). However, one optimization that hails all the way back to cb115748ec0d (Some more memory leak avoidance, 2006-06-17) is to release the commit's list of parents immediately after showing it _and to set that parent list to `NULL`_. This can break the merge base computation. This problem is most obvious when traversing the commits in reverse: In that instance, if a parent of a merge commit has been shown as part of the `git log` command, by the time the merge commit's diff needs to be computed, that parent commit's list of parent commits will have been set to `NULL` and as a result no merge base will be found (even if one should be found). Traversing commits in reverse is far from the only circumstance in which this problem occurs, though. There are many avenues to traversing at least one commit in the revision walk that will later be part of a merge base computation, for example when not even walking any revisions in `git show ` where `` is part of the commit graph between the parents of ``. Another way to force a scenario where a commit is traversed before it has to be traversed again as part of a merge base computation is to start with two revisions (where the first one is reachable from the second but not in a first-parent ancestry) and show the commit log with `--topo-order` and `--first-parent`. Let's fix this by special-casing the `remerge_diff` mode, similar to what we did with reflogs in f35650dff6a4 (log: do not free parents when walking reflog, 2017-07-07). Signed-off-by: Johannes Schindelin --- builtin/log.c | 8 ++++++-- t/t4069-remerge-diff.sh | 7 +++++++ 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/builtin/log.c b/builtin/log.c index c0a8bb95e9830b..2f88a3e607d14e 100644 --- a/builtin/log.c +++ b/builtin/log.c @@ -522,10 +522,14 @@ static int cmd_log_walk_no_free(struct rev_info *rev) * but we didn't actually show the commit. */ rev->max_count++; - if (!rev->reflog_info) { + if (!rev->reflog_info && !rev->remerge_diff) { /* * We may show a given commit multiple times when - * walking the reflogs. + * walking the reflogs. Therefore we still need it. + * + * Likewise, we potentially still need the parents + * of * already shown commits to determine merge + * bases when showing remerge diffs. */ free_commit_buffer(the_repository->parsed_objects, commit); diff --git a/t/t4069-remerge-diff.sh b/t/t4069-remerge-diff.sh index 07323ebafe0d0c..a68c6bfa0364d0 100755 --- a/t/t4069-remerge-diff.sh +++ b/t/t4069-remerge-diff.sh @@ -317,4 +317,11 @@ test_expect_success 'remerge-diff turns off history simplification' ' test_cmp expect actual ' +test_expect_success 'remerge-diff with --reverse' ' + git log -1 --remerge-diff --oneline ab_resolution^ >expect && + git log -1 --remerge-diff --oneline ab_resolution >>expect && + git log -2 --remerge-diff --oneline ab_resolution --reverse >actual && + test_cmp expect actual +' + test_done