🔧: Depend on typing_extensions only on Python <3.8 (#642)

myst_parser/_compat.py

@@ -1,8 +1,14 @@
 """Helpers for cross compatibility across dependency versions."""
+import sys
 from typing import Callable, Iterable
 
 from docutils.nodes import Element
 
+if sys.version_info >= (3, 8):
+    from typing import Literal, Protocol, get_args, get_origin  # noqa: F401
+else:
+    from typing_extensions import Literal, Protocol, get_args, get_origin  # noqa: F401
+
 
 def findall(node: Element) -> Callable[..., Iterable[Element]]:
     """Iterate through"""

myst_parser/_docs.py

@@ -10,8 +10,8 @@
 from sphinx.directives import other
 from sphinx.util import logging
 from sphinx.util.docutils import SphinxDirective
-from typing_extensions import get_args, get_origin
 
+from ._compat import get_args, get_origin
 from .config.main import MdParserConfig
 from .parsers.docutils_ import Parser as DocutilsParser
 

myst_parser/config/dc_validators.py

@@ -4,7 +4,7 @@
 import dataclasses as dc
 from typing import Any, Sequence
 
-from typing_extensions import Protocol
+from myst_parser._compat import Protocol
 
 
 def validate_field(inst: Any, field: dc.Field, value: Any) -> None:

myst_parser/parsers/docutils_.py

@@ -5,8 +5,8 @@
 from docutils import frontend, nodes
 from docutils.core import default_description, publish_cmdline
 from docutils.parsers.rst import Parser as RstParser
-from typing_extensions import Literal, get_args, get_origin
 
+from myst_parser._compat import Literal, get_args, get_origin
 from myst_parser.config.main import (
     MdParserConfig,
     TopmatterReadError,

pyproject.toml

@@ -40,7 +40,7 @@ dependencies = [
     "mdit-py-plugins~=0.3.1",
     "pyyaml",
     "sphinx>=4,<6",
-    "typing-extensions",
+    'typing-extensions; python_version < "3.8"',
 ]
 
 [project.urls]

tests/test_docutils.py

@@ -4,8 +4,8 @@
 
 import pytest
 from docutils import VersionInfo, __version_info__
-from typing_extensions import Literal
 
+from myst_parser._compat import Literal
 from myst_parser.mdit_to_docutils.base import make_document
 from myst_parser.parsers.docutils_ import (
     Parser,