[PATCH v2] rebase: ignore non-branch update-refs

[mail@abhinavg.net]

From: Abhinav Gupta <mail@abhinavg.net>

The following Git configuration breaks git rebase --update-refs:

    [rebase]
        instructionFormat = %s%d

The '%d' format requests all available decorations for a commit,
filling the global decoration table with all of them,
which --update-refs then uses to populate 'update-ref' instructions
in the rebase todo list.

Specifically, this results in the following instruction:

    update-ref HEAD

The todo parser then rejects the instruction:

    error: update-ref requires a fully qualified refname e.g. refs/heads/HEAD
    error: invalid line 3: update-ref HEAD

To fix, ignore decorations that are not local branches
when scanning through the table.

This matches the documented contract:
it moves branch refs under refs/heads/
and leaves display-only decorations (HEAD, tags, etc.) alone.

Verification:
A regression test that fails without this fix is included.

Signed-off-by: Abhinav Gupta <mail@abhinavg.net>
---
Updates:
    v2: incorporate suggestions to simplify the test

 sequencer.c                   | 10 ++++++++++
 t/t3404-rebase-interactive.sh | 18 ++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/sequencer.c b/sequencer.c
index b7d8dca47f..25bcfc5da0 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -6428,6 +6428,16 @@ static int add_decorations_to_list(const struct commit *commit,
 		const char *path;
 		size_t base_offset = ctx->buf->len;
 
+		/*
+		 * The global decoration table may contain names loaded by
+		 * a previous pretty format such as "%d".
+		 * This will result in refs such as "HEAD" being present.
+		 */
+		if (decoration->type != DECORATION_REF_LOCAL) {
+			decoration = decoration->next;
+			continue;
+		}
+
 		/*
 		 * If the branch is the current HEAD, then it will be
 		 * updated by the default rebase behavior.
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 3e44562afa..58b3bb0c27 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1960,6 +1960,24 @@ test_expect_success '--update-refs adds commands with --rebase-merges' '
 	)
 '
 
+test_expect_success '--update-refs ignores non-branch decorations' '
+	test_when_finished "git branch -D update-refs" &&
+	test_when_finished "git checkout primary" &&
+	git checkout -B update-refs no-conflict-branch &&
+	(
+		set_cat_todo_editor &&
+
+		# rebase.instructionFormat=%d loads normal log decorations before
+		# --update-refs adds its branch placeholders so we must ignore
+		# all non-local decorations.
+		test_must_fail git -c rebase.instructionFormat="%s%d" \
+			rebase -i --update-refs HEAD^ >todo
+	) &&
+	grep ^update-ref todo >actual &&
+	test_write_lines "update-ref refs/heads/no-conflict-branch" >expect &&
+	test_cmp expect actual
+'
+
 test_expect_success '--update-refs updates refs correctly' '
 	git checkout -B update-refs no-conflict-branch &&
 	git branch -f base HEAD~4 &&

base-commit: 94f057755b7941b321fd11fec1b2e3ca5313a4e0
-- 
2.54.0