refs: add git_reference_has_log()

include/git2/refs.h

@@ -353,6 +353,16 @@ GIT_EXTERN(int) git_reference_foreach_glob(
 		void *payload
 );
 
+/**
+ * Check if a reflog exists for the specified reference.
+ *
+ * @param ref A git reference
+ *
+ * @return 0 when no reflog can be found, 1 when it exists;
+ * otherwise an error code.
+ */
+GIT_EXTERN(int) git_reference_has_log(git_reference *ref);
+
 /** @} */
 GIT_END_DECL
 #endif

src/refs.c

@@ -1802,3 +1802,20 @@ int git_reference_foreach_glob(
 	return git_reference_foreach(
 			repo, list_flags, fromglob_cb, &data);
 }
+
+int git_reference_has_log(
+	git_reference *ref)
+{
+	git_buf path = GIT_BUF_INIT;
+	int result;
+
+	assert(ref);
+
+	if (git_buf_join_n(&path, '/', 3, ref->owner->path_repository, GIT_REFLOG_DIR, ref->name) < 0)
+		return -1;
+
+	result = git_path_isfile(git_buf_cstr(&path));
+	git_buf_free(&path);
+
+	return result;
+}

tests-clar/refs/reflog.c

@@ -145,3 +145,20 @@ void test_refs_reflog__renaming_the_reference_moves_the_reflog(void)
 	git_buf_free(&moved_log_path);
 	git_buf_free(&master_log_path);
 }
+static void assert_has_reflog(bool expected_result, const char *name)
+{
+	git_reference *ref;
+
+	cl_git_pass(git_reference_lookup(&ref, g_repo, name));
+
+	cl_assert_equal_i(expected_result, git_reference_has_log(ref));
+
+	git_reference_free(ref);
+}
+
+void test_refs_reflog__reference_has_reflog(void)
+{
+	assert_has_reflog(true, "HEAD");
+	assert_has_reflog(true, "refs/heads/master");
+	assert_has_reflog(false, "refs/heads/subtrees");
+}