From e8b0554b2ba0bad884d619084b2561aaaae048a2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?B=C3=A9n=C3=A9dikt=20Tran?=
 <10796600+picnixz@users.noreply.github.com>
Date: Thu, 1 Feb 2024 15:34:06 +0100
Subject: [PATCH 1/2] Fix type comments crash inside generic definitions

---
 mypy/expandtype.py                       | 12 +++++-
 test-data/unit/check-typevar-values.test | 52 ++++++++++++++++++++++++
 2 files changed, 63 insertions(+), 1 deletion(-)

diff --git a/mypy/expandtype.py b/mypy/expandtype.py
index f6aa74add9d8..160b1011fef5 100644
--- a/mypy/expandtype.py
+++ b/mypy/expandtype.py
@@ -2,7 +2,7 @@
 
 from typing import Final, Iterable, Mapping, Sequence, TypeVar, cast, overload
 
-from mypy.nodes import ARG_STAR, Var
+from mypy.nodes import ARG_STAR, FakeInfo, Var
 from mypy.state import state
 from mypy.types import (
     ANY_STRATEGY,
@@ -212,6 +212,16 @@ def visit_erased_type(self, t: ErasedType) -> Type:
 
     def visit_instance(self, t: Instance) -> Type:
         args = self.expand_types_with_unpack(list(t.args))
+
+        if isinstance(t.type, FakeInfo):
+            # The type checker expands function definitions and bodies
+            # if they depend on constrained type variables but the body
+            # might contain a tuple type comment (e.g., # type: (int, float)),
+            # in which case 't.type' is not yet available.
+            #
+            # See: https://github.com/python/mypy/issues/16649
+            return t.copy_modified(args=args)
+
         if t.type.fullname == "builtins.tuple":
             # Normalize Tuple[*Tuple[X, ...], ...] -> Tuple[X, ...]
             arg = args[0]
diff --git a/test-data/unit/check-typevar-values.test b/test-data/unit/check-typevar-values.test
index effaf620f1f0..4ab65f1522e1 100644
--- a/test-data/unit/check-typevar-values.test
+++ b/test-data/unit/check-typevar-values.test
@@ -706,3 +706,55 @@ Func = Callable[[], T]
 
 class A: ...
 class B: ...
+
+[case testTypeCommentInGenericTypeWithConstrainedTypeVar]
+from typing import Generic, TypeVar
+
+NT = TypeVar("NT", int, float)
+
+class Foo1(Generic[NT]):
+    p = 1  # type: int
+
+class Foo2(Generic[NT]):
+    p, q = 1, 2.0  # type: (int, float)
+
+class Foo3(Generic[NT]):
+    def bar(self) -> None:
+        p = 1  # type: int
+
+class Foo4(Generic[NT]):
+    def bar(self) -> None:
+        p, q = 1, 2.0  # type: (int, float)
+
+def foo3(x: NT) -> None:
+    p = 1  # type: int
+
+def foo4(x: NT) -> None:
+    p, q = 1, 2.0  # type: (int, float)
+[builtins fixtures/tuple.pyi]
+
+[case testTypeCommentInGenericTypeWithBoundedTypeVar]
+from typing import Generic, TypeVar
+
+NT = TypeVar("NT", bound=int)
+
+class Foo1(Generic[NT]):
+    p = 1  # type: int
+
+class Foo2(Generic[NT]):
+    p, q = 1, 2.0  # type: (int, float)
+
+class Foo3(Generic[NT]):
+    def bar(self) -> None:
+        p = 1  # type: int
+
+class Foo4(Generic[NT]):
+    def bar(self) -> None:
+        p, q = 1, 2.0  # type: (int, float)
+
+def foo3(x: NT) -> None:
+    p = 1  # type: int
+
+def foo4(x: NT) -> None:
+    p, q = 1, 2.0  # type: (int, float)
+[builtins fixtures/tuple.pyi]

From 472fcf100d7272573865cfae4478fe2af8988808 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?B=C3=A9n=C3=A9dikt=20Tran?=
 <10796600+picnixz@users.noreply.github.com>
Date: Thu, 1 Feb 2024 15:44:13 +0100
Subject: [PATCH 2/2] remove unnecessary test

---
 test-data/unit/check-typevar-values.test | 26 ------------------------
 1 file changed, 26 deletions(-)

diff --git a/test-data/unit/check-typevar-values.test b/test-data/unit/check-typevar-values.test
index 4ab65f1522e1..8b961d88d23d 100644
--- a/test-data/unit/check-typevar-values.test
+++ b/test-data/unit/check-typevar-values.test
@@ -732,29 +732,3 @@ def foo3(x: NT) -> None:
 def foo4(x: NT) -> None:
     p, q = 1, 2.0  # type: (int, float)
 [builtins fixtures/tuple.pyi]
-
-[case testTypeCommentInGenericTypeWithBoundedTypeVar]
-from typing import Generic, TypeVar
-
-NT = TypeVar("NT", bound=int)
-
-class Foo1(Generic[NT]):
-    p = 1  # type: int
-
-class Foo2(Generic[NT]):
-    p, q = 1, 2.0  # type: (int, float)
-
-class Foo3(Generic[NT]):
-    def bar(self) -> None:
-        p = 1  # type: int
-
-class Foo4(Generic[NT]):
-    def bar(self) -> None:
-        p, q = 1, 2.0  # type: (int, float)
-
-def foo3(x: NT) -> None:
-    p = 1  # type: int
-
-def foo4(x: NT) -> None:
-    p, q = 1, 2.0  # type: (int, float)
-[builtins fixtures/tuple.pyi]