From 30850455b96a804094bfba99b71119c989976280 Mon Sep 17 00:00:00 2001
From: Marc Mueller <30130371+cdce8p@users.noreply.github.com>
Date: Mon, 19 Dec 2022 11:41:56 +0100
Subject: [PATCH] Add basic support for typing_extensions.TypeVar

---
 mypy/semanal.py                               |  2 +-
 test-data/unit/check-generics.test            | 33 +++++++++++++++++++
 test-data/unit/lib-stub/typing_extensions.pyi |  7 ++--
 3 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/mypy/semanal.py b/mypy/semanal.py
index fee66ae9b2ccf..9160097028305 100644
--- a/mypy/semanal.py
+++ b/mypy/semanal.py
@@ -3847,7 +3847,7 @@ def process_typevar_declaration(self, s: AssignmentStmt) -> bool:
         Return True if this looks like a type variable declaration (but maybe
         with errors), otherwise return False.
         """
-        call = self.get_typevarlike_declaration(s, ("typing.TypeVar",))
+        call = self.get_typevarlike_declaration(s, ("typing.TypeVar", "typing_extensions.TypeVar"))
         if not call:
             return False
 
diff --git a/test-data/unit/check-generics.test b/test-data/unit/check-generics.test
index dd7e31528a4fe..27441ce908fe8 100644
--- a/test-data/unit/check-generics.test
+++ b/test-data/unit/check-generics.test
@@ -2663,3 +2663,36 @@ def foo(x: A) -> A:
                 # N: (Hint: Use "B" in function signature to bind "B" inside a function)
         return y.x
     return bar()[0]
+
+
+-- TypeVar imported from typing_extensions
+-- ---------------------------------------
+
+[case testTypeVarTypingExtensionsSimpleGeneric]
+from typing import Generic
+from typing_extensions import TypeVar
+
+T = TypeVar("T")
+
+class A(Generic[T]):
+    def __init__(self, value: T) -> None:
+        self.value = value
+
+a: A = A(8)
+b: A[str] = A("")
+
+reveal_type(A(1.23))  # N: Revealed type is "__main__.A[builtins.float]"
+
+[builtins fixtures/tuple.pyi]
+
+[case testTypeVarTypingExtensionsSimpleBound]
+from typing_extensions import TypeVar
+
+T= TypeVar("T")
+
+def func(var: T) -> T:
+    return var
+
+reveal_type(func(1))  # N: Revealed type is "builtins.int"
+
+[builtins fixtures/tuple.pyi]
diff --git a/test-data/unit/lib-stub/typing_extensions.pyi b/test-data/unit/lib-stub/typing_extensions.pyi
index e92f7e9135027..cbf692fc71111 100644
--- a/test-data/unit/lib-stub/typing_extensions.pyi
+++ b/test-data/unit/lib-stub/typing_extensions.pyi
@@ -1,10 +1,11 @@
-from typing import TypeVar, Any, Mapping, Iterator, NoReturn as NoReturn, Dict, Type
+import typing
+from typing import Any, Mapping, Iterator, NoReturn as NoReturn, Dict, Type
 from typing import TYPE_CHECKING as TYPE_CHECKING
 from typing import NewType as NewType, overload as overload
 
 import sys
 
-_T = TypeVar('_T')
+_T = typing.TypeVar('_T')
 
 class _SpecialForm:
     def __getitem__(self, typeargs: Any) -> Any:
@@ -25,6 +26,8 @@ Literal: _SpecialForm = ...
 
 Annotated: _SpecialForm = ...
 
+TypeVar: _SpecialForm
+
 ParamSpec: _SpecialForm
 Concatenate: _SpecialForm