[PATCH 6/8] sequencer: handle autosquash and post-rewrite for merge commands

[Johannes Schindelin <johannes.schindelin@gmx.de>]

In the previous patches, we implemented the basic functionality of the
`git rebase -i --recreate-merges` command, in particular the `merge`
command to create merge commits in the sequencer.

The interactive rebase is a lot more these days, though, than a simple
cherry-pick in a loop. For example, it calls the post-rewrite hook (if
any) after rebasing with a mapping of the old->new commits. And the
interactive rebase also supports the autosquash mode, where commits
whose oneline is of the form `fixup! <oneline>` or `squash! <oneline>`
are rearranged to amend commits whose oneline they match.

This patch implements the post-rewrite and autosquash handling for the
`merge` command we just introduced. The other commands that were added
recently (`label`, `reset` and `bud`) do not create new commits,
therefore post-rewrite & autosquash do not need to handle them.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 refs.c                            |  3 ++-
 sequencer.c                       | 10 +++++++---
 t/t3430-rebase-recreate-merges.sh | 39 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 48 insertions(+), 4 deletions(-)

diff --git a/refs.c b/refs.c
index 20ba82b4343..e8b84c189ff 100644
--- a/refs.c
+++ b/refs.c
@@ -600,7 +600,8 @@ int dwim_log(const char *str, int len, struct object_id *oid, char **log)
 static int is_per_worktree_ref(const char *refname)
 {
 	return !strcmp(refname, "HEAD") ||
-		starts_with(refname, "refs/bisect/");
+		starts_with(refname, "refs/bisect/") ||
+		starts_with(refname, "refs/rewritten/");
 }
 
 static int is_pseudoref_syntax(const char *refname)
diff --git a/sequencer.c b/sequencer.c
index 1bef16647b4..b63bfb9a141 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2413,10 +2413,13 @@ static int pick_commits(struct todo_list *todo_list, struct replay_opts *opts)
 			res = do_reset(item->arg, item->arg_len);
 		else if (item->command == TODO_BUD)
 			res = do_reset("onto", 4);
-		else if (item->command == TODO_MERGE)
+		else if (item->command == TODO_MERGE) {
 			res = do_merge(item->commit,
 				       item->arg, item->arg_len, opts);
-		else if (!is_noop(item->command))
+			if (item->commit)
+				record_in_rewritten(&item->commit->object.oid,
+						    peek_command(todo_list, 1));
+		} else if (!is_noop(item->command))
 			return error(_("unknown command %d"), item->command);
 
 		todo_list->current++;
@@ -3556,7 +3559,8 @@ int rearrange_squash(void)
 		struct subject2item_entry *entry;
 
 		next[i] = tail[i] = -1;
-		if (item->command >= TODO_EXEC) {
+		if (item->command >= TODO_EXEC &&
+		    (item->command != TODO_MERGE || !item->commit)) {
 			subjects[i] = NULL;
 			continue;
 		}
diff --git a/t/t3430-rebase-recreate-merges.sh b/t/t3430-rebase-recreate-merges.sh
index 46ae52f88b3..76e615bd7c1 100755
--- a/t/t3430-rebase-recreate-merges.sh
+++ b/t/t3430-rebase-recreate-merges.sh
@@ -143,4 +143,43 @@ test_expect_success 'with a branch tip that was cherry-picked already' '
 	EOF
 '
 
+test_expect_success 'refs/rewritten/* is worktree-local' '
+	git worktree add wt &&
+	cat >wt/script-from-scratch <<-\EOF &&
+	label xyz
+	exec GIT_DIR=../.git git rev-parse --verify refs/rewritten/xyz >a || :
+	exec git rev-parse --verify refs/rewritten/xyz >b
+	EOF
+
+	test_config -C wt sequence.editor \""$PWD"/replace-editor.sh\" &&
+	git -C wt rebase -i HEAD &&
+	test_must_be_empty wt/a &&
+	test_cmp_rev HEAD "$(cat wt/b)"
+'
+
+test_expect_success 'post-rewrite hook and fixups work for merges' '
+	git checkout -b post-rewrite &&
+	test_commit same1 &&
+	git reset --hard HEAD^ &&
+	test_commit same2 &&
+	git merge -m "to fix up" same1 &&
+	echo same old same old >same2.t &&
+	test_tick &&
+	git commit --fixup HEAD same2.t &&
+	fixup="$(git rev-parse HEAD)" &&
+
+	mkdir -p .git/hooks &&
+	test_when_finished "rm .git/hooks/post-rewrite" &&
+	echo "cat >actual" | write_script .git/hooks/post-rewrite &&
+
+	test_tick &&
+	git rebase -i --autosquash --recreate-merges HEAD^^^ &&
+	printf "%s %s\n%s %s\n%s %s\n%s %s\n" >expect $(git rev-parse \
+		$fixup^^2 HEAD^2 \
+		$fixup^^ HEAD^ \
+		$fixup^ HEAD \
+		$fixup HEAD) &&
+	test_cmp expect actual
+'
+
 test_done
-- 
2.15.1.windows.2.1430.ga56c4f9e2a9