The `git merge` command does not allow merging commits that are already
reachable from HEAD: `git merge HEAD^`, for example, will report that we
are already up to date and not change a thing.
In an interactive rebase, such a merge could occur previously, e.g. when
competing (or slightly modified) versions of a patch series were applied
upstream, and the user had to `git rebase --skip` all of the local
commits, and the topic branch becomes "empty" as a consequence.
Let's teach the todo command `merge` to behave the same as `git merge`.
Seeing as it requires some low-level trickery to create such merges with
Git's commands in the first place, we do not even have to bother to
introduce an option to force `merge` to create such merge commits.
Signed-off-by: Johannes Schindelin <johannes.schindelin@xxxxxx>
---
sequencer.c | 7 +++++++
t/t3430-rebase-merges.sh | 8 ++++++++
2 files changed, 15 insertions(+)
diff --git a/sequencer.c b/sequencer.c
index f3b4fe4d75f..443a0a0ee87 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2803,6 +2803,13 @@ static int do_merge(struct commit *commit, const char *arg, int arg_len,
write_message("no-ff", 5, git_path_merge_mode(), 0);
bases = get_merge_bases(head_commit, merge_commit);
+ if (bases && !oidcmp(&merge_commit->object.oid,
+ &bases->item->object.oid)) {
+ ret = 0;
+ /* skip merging an ancestor of HEAD */
+ goto leave_merge;
+ }
+
for (j = bases; j; j = j->next)
commit_list_insert(j->item, &reversed);
free_commit_list(bases);
diff --git a/t/t3430-rebase-merges.sh b/t/t3430-rebase-merges.sh
index e9c5dc1cd95..1628c8dcc20 100755
--- a/t/t3430-rebase-merges.sh
+++ b/t/t3430-rebase-merges.sh
@@ -215,4 +215,12 @@ test_expect_success 'post-rewrite hook and fixups work for merges' '
test_cmp expect actual
'
+test_expect_success 'refuse to merge ancestors of HEAD' '
+ echo "merge HEAD^" >script-from-scratch &&
+ test_config -C wt sequence.editor \""$PWD"/replace-editor.sh\" &&
+ before="$(git rev-parse HEAD)" &&
+ git rebase -i HEAD &&
+ test_cmp_rev HEAD $before
+'
+
test_done
--
2.17.0.windows.1.15.gaa56ade3205
