Recognise LiteralString as str (#12559)

Linking #12554

Co-authored-by: hauntsaninja <>

Author: hauntsaninja

mypy/nodes.py

@@ -123,6 +123,8 @@ def get_column(self) -> int:
     'typing.DefaultDict': 'collections.defaultdict',
     'typing.Deque': 'collections.deque',
     'typing.OrderedDict': 'collections.OrderedDict',
+    # HACK: a lie in lieu of actual support for PEP 675
+    'typing.LiteralString': 'builtins.str',
 }
 
 # This keeps track of the oldest supported Python version where the corresponding
@@ -137,12 +139,15 @@ def get_column(self) -> int:
     'typing.DefaultDict': (2, 7),
     'typing.Deque': (2, 7),
     'typing.OrderedDict': (3, 7),
+    'typing.LiteralString': (3, 11),
 }
 
 # This keeps track of aliases in `typing_extensions`, which we treat specially.
 typing_extensions_aliases: Final = {
     # See: https://github.com/python/mypy/issues/11528
     'typing_extensions.OrderedDict': 'collections.OrderedDict',
+    # HACK: a lie in lieu of actual support for PEP 675
+    'typing_extensions.LiteralString': 'builtins.str',
 }
 
 reverse_builtin_aliases: Final = {
@@ -156,6 +161,8 @@ def get_column(self) -> int:
 _nongen_builtins.update((name, alias) for alias, name in type_aliases.items())
 # Drop OrderedDict from this for backward compatibility
 del _nongen_builtins['collections.OrderedDict']
+# HACK: consequence of hackily treating LiteralString as an alias for str
+del _nongen_builtins['builtins.str']
 
 
 def get_nongen_builtins(python_version: Tuple[int, int]) -> Dict[str, str]:

test-data/unit/check-type-aliases.test

@@ -752,3 +752,21 @@ from typing_extensions import TypeAlias
 A: TypeAlias = str
 [builtins fixtures/bool.pyi]
 [out]
+
+
+[case testLiteralStringPep675]
+# flags: --python-version 3.11
+from typing import LiteralString as tpLS
+from typing_extensions import LiteralString as tpxLS
+
+def f(a: tpLS, b: tpxLS) -> None:
+    reveal_type(a)  # N: Revealed type is "builtins.str"
+    reveal_type(b)  # N: Revealed type is "builtins.str"
+
+# This isn't the correct behaviour, but should unblock use of LiteralString in typeshed
+f("asdf", "asdf")
+string: str
+f(string, string)
+
+[builtins fixtures/tuple.pyi]
+[typing fixtures/typing-medium.pyi]

test-data/unit/fixtures/typing-medium.pyi

@@ -27,6 +27,7 @@ TypedDict = 0
 NoReturn = 0
 NewType = 0
 TypeAlias = 0
+LiteralString = 0
 
 T = TypeVar('T')
 T_co = TypeVar('T_co', covariant=True)