rebase: skip branch symref aliases

git rebase --update-refs can fail after the normal rebase path has
updated the current branch when another local branch is a symref to it.
This can happen during a default-branch rename where refs/heads/main
points at refs/heads/master while users migrate.

The sequencer queues update-ref commands from local branch decorations.
Commit 106b688 (rebase: ignore non-branch update-refs) filters out
decorations that are not local branches, such as HEAD and tags. A branch
symref is different: it is still a local branch decoration, but if it
resolves to another branch then that target branch is itself present in
the decoration list and will be updated as a concrete branch.

Skip branch decorations whose symrefs resolve to refs/heads/*, because
those targets are already represented by concrete branch decorations.
This prevents aliases from scheduling a second update for the same
branch.

Resolve remaining local branch decorations before checking whether they
are checked out, but only skip the current branch when it is not
reported as checked out. This preserves the existing todo-list comment
for checked-out branches while still avoiding an update-ref command for
the current branch when no checked-out protection is needed.

Symrefs to other branches are skipped directly. Other symrefs stay on
the existing path, but checked-out protection is applied to the resolved
target rather than to the symref name.

Signed-off-by: Son Luong Ngoc <sluongng@gmail.com>

Author: sluongng

sequencer.c

@@ -6465,28 +6465,49 @@ static int add_decorations_to_list(const struct commit *commit,
 				   struct todo_add_branch_context *ctx)
 {
 	const struct name_decoration *decoration = get_name_decoration(&commit->object);
-	const char *head_ref = refs_resolve_ref_unsafe(get_main_ref_store(the_repository),
-						       "HEAD",
-						       RESOLVE_REF_READING,
-						       NULL,
-						       NULL);
+	struct ref_store *refs = get_main_ref_store(the_repository);
+	char *head_ref = refs_resolve_refdup(refs, "HEAD",
+					     RESOLVE_REF_READING,
+					     NULL, NULL);
 
 	while (decoration) {
 		struct todo_item *item;
 		const char *path;
+		const char *checked_ref;
+		char *resolved_ref;
+		int flags = 0;
 		size_t base_offset = ctx->buf->len;
 
 		/*
-		 * If the branch is the current HEAD, then it will be
-		 * updated by the default rebase behavior.
-		 * Exclude it from the list of refs to update,
-		 * as well as any non-branch decorations.
 		 * Non-branch decorations may be present if the pretty format
 		 * includes "%d", which would have loaded all refs
 		 * into the global decoration table.
 		 */
-		if ((head_ref && !strcmp(head_ref, decoration->name)) ||
-		    (decoration->type != DECORATION_REF_LOCAL)) {
+		if (decoration->type != DECORATION_REF_LOCAL) {
+			decoration = decoration->next;
+			continue;
+		}
+
+		resolved_ref = refs_resolve_refdup(refs, decoration->name,
+						      RESOLVE_REF_READING,
+						      NULL, &flags);
+		if (resolved_ref && (flags & REF_ISSYMREF) &&
+		    starts_with(resolved_ref, "refs/heads/")) {
+			free(resolved_ref);
+			decoration = decoration->next;
+			continue;
+		}
+
+		checked_ref = (resolved_ref && (flags & REF_ISSYMREF)) ?
+			resolved_ref : decoration->name;
+		path = branch_checked_out(checked_ref);
+
+		/*
+		 * If the branch is the current HEAD, then it will be
+		 * updated by the default rebase behavior.
+		 */
+		if (!path && head_ref && !strcmp(head_ref, decoration->name)) {
+			free(resolved_ref);
 			decoration = decoration->next;
 			continue;
 		}
@@ -6498,7 +6519,7 @@ static int add_decorations_to_list(const struct commit *commit,
 		memset(item, 0, sizeof(*item));
 
 		/* If the branch is checked out, then leave a comment instead. */
-		if ((path = branch_checked_out(decoration->name))) {
+		if (path) {
 			item->command = TODO_COMMENT;
 			strbuf_commented_addf(ctx->buf, comment_line_str,
 					      "Ref %s checked out at '%s'\n",
@@ -6518,9 +6539,11 @@ static int add_decorations_to_list(const struct commit *commit,
 		item->arg_len = ctx->buf->len - base_offset;
 		ctx->items_nr++;
 
+		free(resolved_ref);
 		decoration = decoration->next;
 	}
 
+	free(head_ref);
 	return 0;
 }
 

t/t3404-rebase-interactive.sh

@@ -1979,20 +1979,35 @@ test_expect_success '--update-refs ignores non-branch decorations' '
 '
 
 test_expect_success '--update-refs updates refs correctly' '
+	test_when_finished "
+		test_might_fail git symbolic-ref -d refs/heads/no-conflict-branch-alias &&
+		test_might_fail git symbolic-ref -d refs/heads/second-alias
+	" &&
 	git checkout -B update-refs no-conflict-branch &&
 	git branch -f base HEAD~4 &&
 	git branch -f first HEAD~3 &&
 	git branch -f second HEAD~3 &&
 	git branch -f third HEAD~1 &&
+	git symbolic-ref refs/heads/no-conflict-branch-alias \
+		refs/heads/no-conflict-branch &&
+	git symbolic-ref refs/heads/second-alias refs/heads/second &&
 	test_commit extra2 fileX &&
 	git commit --amend --fixup=L &&
 
 	git rebase -i --autosquash --update-refs primary 2>err &&
 
 	test_cmp_rev HEAD~3 refs/heads/first &&
 	test_cmp_rev HEAD~3 refs/heads/second &&
+	test_cmp_rev HEAD~3 refs/heads/second-alias &&
 	test_cmp_rev HEAD~1 refs/heads/third &&
 	test_cmp_rev HEAD refs/heads/no-conflict-branch &&
+	test_cmp_rev HEAD refs/heads/no-conflict-branch-alias &&
+	test_write_lines refs/heads/no-conflict-branch >expect &&
+	git symbolic-ref refs/heads/no-conflict-branch-alias >actual &&
+	test_cmp expect actual &&
+	test_write_lines refs/heads/second >expect &&
+	git symbolic-ref refs/heads/second-alias >actual &&
+	test_cmp expect actual &&
 
 	q_to_tab >expect <<-\EOF &&
 	Successfully rebased and updated refs/heads/update-refs.