Merge branch 'tc/replay-down-to-root' into seen

git replay now supports replaying down to the root commit.

* tc/replay-down-to-root:
  replay: support replaying down from root commit

Author: gitster

replay.c

@@ -271,12 +271,18 @@ static struct commit *pick_regular_commit(struct repository *repo,
 	struct commit *base, *replayed_base;
 	struct tree *pickme_tree, *base_tree, *replayed_base_tree;
 
-	base = pickme->parents->item;
-	replayed_base = mapped_commit(replayed_commits, base, onto);
+	if (pickme->parents) {
+		base = pickme->parents->item;
+		replayed_base = mapped_commit(replayed_commits, base, onto);
+		base_tree = repo_get_commit_tree(repo, base);
+	} else {
+		base = NULL;
+		replayed_base = onto;
+		base_tree = lookup_tree(repo, repo->hash_algo->empty_tree);
+	}
 
 	replayed_base_tree = repo_get_commit_tree(repo, replayed_base);
 	pickme_tree = repo_get_commit_tree(repo, pickme);
-	base_tree = repo_get_commit_tree(repo, base);
 
 	if (mode == REPLAY_MODE_PICK) {
 		/* Cherry-pick: normal order */
@@ -364,8 +370,6 @@ int replay_revisions(struct rev_info *revs,
 	set_up_replay_mode(revs->repo, &revs->cmdline, opts->onto,
 			   &detached_head, &advance, &revert, &onto, &update_refs);
 
-	/* FIXME: Should allow replaying commits with the first as a root commit */
-
 	if (prepare_revision_walk(revs) < 0) {
 		ret = error(_("error preparing revisions"));
 		goto out;
@@ -380,9 +384,7 @@ int replay_revisions(struct rev_info *revs,
 		khint_t pos;
 		int hr;
 
-		if (!commit->parents)
-			die(_("replaying down from root commit is not supported yet!"));
-		if (commit->parents->next)
+		if (commit->parents && commit->parents->next)
 			die(_("replaying merge commits is not supported yet!"));
 
 		last_commit = pick_regular_commit(revs->repo, commit, replayed_commits,

t/t3650-replay-basics.sh

@@ -81,9 +81,13 @@ test_expect_success 'exactly one of --onto, --advance, or --revert is required'
 	test_cmp expect actual
 '
 
-test_expect_success 'no base or negative ref gives no-replaying down to root error' '
-	echo "fatal: replaying down from root commit is not supported yet!" >expect &&
-	test_must_fail git replay --onto=topic1 topic2 2>actual &&
+test_expect_success 'replay down to root onto another branch' '
+	git replay --ref-action=print --onto main topic2 >result &&
+
+	test_line_count = 1 result &&
+
+	git log --format=%s $(cut -f 3 -d " " result) >actual &&
+	test_write_lines E D C M L B A >expect &&
 	test_cmp expect actual
 '