From 82766b29611aea7c3fb42a99debfba1436852d38 Mon Sep 17 00:00:00 2001
From: Phillip Wood <phillip.wood@dunelm.org.uk>
Date: Thu, 10 Nov 2022 16:43:40 +0000
Subject: [PATCH 1/2] sequencer: unify label lookup

The arguments to the `reset` and `merge` commands may be a label created
with a `label` command or an arbitrary commit name. The `merge` command
uses the lookup_label() function to lookup its arguments but `reset` has
a slightly different version of that function in do_reset(). Reduce this
code duplication by calling lookup_label() from do_reset() as well.

This change improves the behavior of `reset` when the argument is a
tree.  Previously `reset` would accept a tree only for the rebase to
fail with

       update_ref failed for ref 'HEAD': cannot update ref 'HEAD': trying to write non-commit object da5497437fd67ca928333aab79c4b4b55036ea66 to branch 'HEAD'

Using lookup_label() means do_reset() will now error out straight away
if its argument is not a commit.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 sequencer.c              | 49 ++++++++++++++++++++--------------------
 t/t3430-rebase-merges.sh |  8 +++++++
 2 files changed, 33 insertions(+), 24 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index f0f1af4d47..f2d0667b57 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -3694,6 +3694,26 @@ static const char *reflog_message(struct replay_opts *opts,
 	return buf.buf;
 }
 
+static struct commit *lookup_label(const char *label, int len,
+				   struct strbuf *buf)
+{
+	struct commit *commit;
+
+	strbuf_reset(buf);
+	strbuf_addf(buf, "refs/rewritten/%.*s", len, label);
+	commit = lookup_commit_reference_by_name(buf->buf);
+	if (!commit) {
+		/* fall back to non-rewritten ref or commit */
+		strbuf_splice(buf, 0, strlen("refs/rewritten/"), "", 0);
+		commit = lookup_commit_reference_by_name(buf->buf);
+	}
+
+	if (!commit)
+		error(_("could not resolve '%s'"), buf->buf);
+
+	return commit;
+}
+
 static int do_reset(struct repository *r,
 		    const char *name, int len,
 		    struct replay_opts *opts)
@@ -3725,6 +3745,7 @@ static int do_reset(struct repository *r,
 		oidcpy(&oid, &opts->squash_onto);
 	} else {
 		int i;
+		struct commit *commit;
 
 		/* Determine the length of the label */
 		for (i = 0; i < len; i++)
@@ -3732,12 +3753,12 @@ static int do_reset(struct repository *r,
 				break;
 		len = i;
 
-		strbuf_addf(&ref_name, "refs/rewritten/%.*s", len, name);
-		if (get_oid(ref_name.buf, &oid) &&
-		    get_oid(ref_name.buf + strlen("refs/rewritten/"), &oid)) {
-			ret = error(_("could not read '%s'"), ref_name.buf);
+		commit = lookup_label(name, len, &ref_name);
+		if (!commit) {
+			ret = -1;
 			goto cleanup;
 		}
+		oid = commit->object.oid;
 	}
 
 	setup_unpack_trees_porcelain(&unpack_tree_opts, "reset");
@@ -3784,26 +3805,6 @@ static int do_reset(struct repository *r,
 	return ret;
 }
 
-static struct commit *lookup_label(const char *label, int len,
-				   struct strbuf *buf)
-{
-	struct commit *commit;
-
-	strbuf_reset(buf);
-	strbuf_addf(buf, "refs/rewritten/%.*s", len, label);
-	commit = lookup_commit_reference_by_name(buf->buf);
-	if (!commit) {
-		/* fall back to non-rewritten ref or commit */
-		strbuf_splice(buf, 0, strlen("refs/rewritten/"), "", 0);
-		commit = lookup_commit_reference_by_name(buf->buf);
-	}
-
-	if (!commit)
-		error(_("could not resolve '%s'"), buf->buf);
-
-	return commit;
-}
-
 static int do_merge(struct repository *r,
 		    struct commit *commit,
 		    const char *arg, int arg_len,
diff --git a/t/t3430-rebase-merges.sh b/t/t3430-rebase-merges.sh
index f351701fec..fbbc4439bf 100755
--- a/t/t3430-rebase-merges.sh
+++ b/t/t3430-rebase-merges.sh
@@ -138,6 +138,14 @@ test_expect_success '`reset` refuses to overwrite untracked files' '
 	git rebase --abort
 '
 
+test_expect_success '`reset` rejects trees' '
+	test_when_finished "test_might_fail git rebase --abort" &&
+	test_must_fail env GIT_SEQUENCE_EDITOR="echo reset A^{tree} >" \
+		git rebase -i B C >out 2>err &&
+	grep "object .* is a tree" err &&
+	test_must_be_empty out
+'
+
 test_expect_success 'failed `merge -C` writes patch (may be rescheduled, too)' '
 	test_when_finished "test_might_fail git rebase --abort" &&
 	git checkout -b conflicting-merge A &&

From 688d82f254f8fc5da019fc4962e6e8646767aba0 Mon Sep 17 00:00:00 2001
From: Phillip Wood <phillip.wood@dunelm.org.uk>
Date: Thu, 10 Nov 2022 16:43:41 +0000
Subject: [PATCH 2/2] sequencer: tighten label lookups

The `label` command creates a ref refs/rewritten/<label> that the
`reset` and `merge` commands resolve by calling lookup_label(). That
uses lookup_commit_reference_by_name() to look up the label ref. As
lookup_commit_reference_by_name() uses the dwim rules when looking up
the label it will look for a branch named
refs/heads/refs/rewritten/<label> and return that instead of an error if
the branch exists and the label does not. Fix this by using read_ref()
followed by lookup_commit_object() when looking up labels.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 sequencer.c              | 14 ++++++++------
 t/t3430-rebase-merges.sh |  9 +++++++++
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index f2d0667b57..7eec231234 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -3694,15 +3694,17 @@ static const char *reflog_message(struct replay_opts *opts,
 	return buf.buf;
 }
 
-static struct commit *lookup_label(const char *label, int len,
-				   struct strbuf *buf)
+static struct commit *lookup_label(struct repository *r, const char *label,
+				   int len, struct strbuf *buf)
 {
 	struct commit *commit;
+	struct object_id oid;
 
 	strbuf_reset(buf);
 	strbuf_addf(buf, "refs/rewritten/%.*s", len, label);
-	commit = lookup_commit_reference_by_name(buf->buf);
-	if (!commit) {
+	if (!read_ref(buf->buf, &oid)) {
+		commit = lookup_commit_object(r, &oid);
+	} else {
 		/* fall back to non-rewritten ref or commit */
 		strbuf_splice(buf, 0, strlen("refs/rewritten/"), "", 0);
 		commit = lookup_commit_reference_by_name(buf->buf);
@@ -3753,7 +3755,7 @@ static int do_reset(struct repository *r,
 				break;
 		len = i;
 
-		commit = lookup_label(name, len, &ref_name);
+		commit = lookup_label(r, name, len, &ref_name);
 		if (!commit) {
 			ret = -1;
 			goto cleanup;
@@ -3852,7 +3854,7 @@ static int do_merge(struct repository *r,
 		k = strcspn(p, " \t\n");
 		if (!k)
 			continue;
-		merge_commit = lookup_label(p, k, &ref_name);
+		merge_commit = lookup_label(r, p, k, &ref_name);
 		if (!merge_commit) {
 			ret = error(_("unable to parse '%.*s'"), k, p);
 			goto leave_merge;
diff --git a/t/t3430-rebase-merges.sh b/t/t3430-rebase-merges.sh
index fbbc4439bf..fa2a06c19f 100755
--- a/t/t3430-rebase-merges.sh
+++ b/t/t3430-rebase-merges.sh
@@ -146,6 +146,15 @@ test_expect_success '`reset` rejects trees' '
 	test_must_be_empty out
 '
 
+test_expect_success '`reset` only looks for labels under refs/rewritten/' '
+	test_when_finished "test_might_fail git rebase --abort" &&
+	git branch refs/rewritten/my-label A &&
+	test_must_fail env GIT_SEQUENCE_EDITOR="echo reset my-label >" \
+		git rebase -i B C >out 2>err &&
+	grep "could not resolve ${SQ}my-label${SQ}" err &&
+	test_must_be_empty out
+'
+
 test_expect_success 'failed `merge -C` writes patch (may be rescheduled, too)' '
 	test_when_finished "test_might_fail git rebase --abort" &&
 	git checkout -b conflicting-merge A &&