fix: Support Literal imported from typing_extensions

Issue mkdocstrings/mkdocstrings#545: mkdocstrings/mkdocstrings#545

src/griffe/agents/nodes.py

@@ -675,7 +675,7 @@ def _get_name_annotation(node: NodeName, parent: Module | Class) -> Name:
 
 def _get_subscript_annotation(node: NodeSubscript, parent: Module | Class) -> Expression:
     left = _get_annotation(node.value, parent)
-    if left.full == "typing.Literal":  # type: ignore[union-attr]
+    if left.full in {"typing.Literal", "typing_extensions.Literal"}:  # type: ignore[union-attr]
         _node_annotation_map[NodeConstant] = _get_literal_annotation
         subscript = _get_annotation(node.slice, parent)
         _node_annotation_map[NodeConstant] = _get_constant_annotation

tests/test_nodes.py

@@ -95,6 +95,8 @@ def _flat(expression: str | Name | Expression) -> list[str | Name]:
     [
         ("import typing\nclass A: ...\na: typing.Literal['A']", False),
         ("from typing import Literal\nclass A: ...\na: Literal['A']", False),
+        ("import typing_extensions\nclass A: ...\na: typing.Literal['A']", False),
+        ("from typing_extensions import Literal\nclass A: ...\na: Literal['A']", False),
         ("from mod import A\na: 'A'", True),
         ("from mod import A\na: list['A']", True),
     ],