Ensure updating HEAD updates reflog

src/refdb_fs.c

@@ -1434,12 +1434,12 @@ success:
 static int reflog_append(refdb_fs_backend *backend, const git_reference *ref, const git_signature *who, const char *message)
 {
 	int error;
-	git_oid old_id, new_id;
+	git_oid old_id, new_id = {{0}};
 	git_buf buf = GIT_BUF_INIT, path = GIT_BUF_INIT;
 	git_repository *repo = backend->repo;
 
 	/* Creation of symbolic references doesn't get a reflog entry */
-	if (ref->type == GIT_REF_SYMBOLIC)
+	if (ref->type == GIT_REF_SYMBOLIC && strcmp(ref->name, GIT_HEAD_FILE))
 		return 0;
 
 	error = git_reference_name_to_id(&old_id, repo, ref->name);
@@ -1450,7 +1450,8 @@ static int reflog_append(refdb_fs_backend *backend, const git_reference *ref, co
 	if (error < 0)
 		return error;
 
-	git_oid_cpy(&new_id, git_reference_target(ref));
+	if (git_reference_target(ref) != NULL)
+		git_oid_cpy(&new_id, git_reference_target(ref));
 
 	if ((error = serialize_reflog_entry(&buf, &old_id, &new_id, who, message)) < 0)
 		goto cleanup;

tests/repo/head.c

@@ -194,3 +194,26 @@ void test_repo_head__can_tell_if_an_unborn_head_is_detached(void)
 
 	cl_assert_equal_i(false, git_repository_head_detached(repo));
 }
+
+void test_repo_head__setting_head_updates_reflog(void)
+{
+	git_reflog *log;
+	const git_reflog_entry *entry1, *entry2, *entry3;
+	git_object *tag;
+
+	cl_git_pass(git_repository_set_head(repo, "refs/heads/haacked", NULL, "message1"));
+	cl_git_pass(git_repository_set_head(repo, "refs/heads/unborn", NULL, "message2"));
+	cl_git_pass(git_revparse_single(&tag, repo, "tags/test"));
+	cl_git_pass(git_repository_set_head_detached(repo, git_object_id(tag), NULL, "message3"));
+
+	cl_git_pass(git_reflog_read(&log, repo, "HEAD"));
+	entry1 = git_reflog_entry_byindex(log, 2);
+	entry2 = git_reflog_entry_byindex(log, 1);
+	entry3 = git_reflog_entry_byindex(log, 0);
+	cl_assert_equal_s("message1", git_reflog_entry_message(entry1));
+	cl_assert_equal_s("message2", git_reflog_entry_message(entry2));
+	cl_assert_equal_s("message3", git_reflog_entry_message(entry3));
+
+	git_reflog_free(log);
+	git_object_free(tag);
+}