Add typing literals for older Python versions

Author: gnikit

fortls/parse_fortran.py

@@ -5,7 +5,12 @@
 import os
 import re
 import sys
-from typing import Literal
+
+# Python < 3.8 does not have typing.Literals
+try:
+    from typing import Literal
+except ImportError:
+    from typing_extensions import Literal
 
 from fortls.constants import (
     DO_TYPE_ID,

setup.cfg

@@ -33,6 +33,7 @@ packages = find:
 python_requires = >= 3.7
 install_requires =
     importlib-metadata; python_version < "3.8"
+    typing-extensions; python_version < "3.8"
 
 [options.package_data]
 fortls = *.json