From df349df9577432e3652312bd6f6a1c7ab184b453 Mon Sep 17 00:00:00 2001
From: wolfgang-aura <169568318+wolfgang-aura@users.noreply.github.com>
Date: Wed, 9 Sep 2026 07:01:39 +0800
Subject: [PATCH 1/2] Fix invalid Self in type parameter bounds (#21960)

---
 mypy/semanal.py                    | 12 ++++++++++--
 test-data/unit/check-selftype.test |  8 ++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/mypy/semanal.py b/mypy/semanal.py
index bceade1b1ac12..877903f1ec1bf 100644
--- a/mypy/semanal.py
+++ b/mypy/semanal.py
@@ -1888,7 +1888,11 @@ def analyze_type_param(
     ) -> TypeVarLikeExpr | None:
         fullname = self.qualified_name(type_param.name)
         if type_param.upper_bound:
-            upper_bound = self.anal_type(type_param.upper_bound, allow_placeholder=True)
+            upper_bound = self.anal_type(
+                type_param.upper_bound,
+                allow_placeholder=True,
+                prohibit_self_type="a type parameter bound",
+            )
             # TODO: we should validate the upper bound is valid for a given kind.
             if upper_bound is None:
                 # This and below copies special-casing for old-style type variables, that
@@ -1929,7 +1933,11 @@ def analyze_type_param(
             values: list[Type] = []
             if type_param.values:
                 for value in type_param.values:
-                    analyzed = self.anal_type(value, allow_placeholder=True)
+                    analyzed = self.anal_type(
+                        value,
+                        allow_placeholder=True,
+                        prohibit_self_type="a type parameter constraint",
+                    )
                     if analyzed is None:
                         analyzed = PlaceholderType(None, [], context.line)
                     if has_type_vars(analyzed):
diff --git a/test-data/unit/check-selftype.test b/test-data/unit/check-selftype.test
index c157200352562..49d3c228d3b27 100644
--- a/test-data/unit/check-selftype.test
+++ b/test-data/unit/check-selftype.test
@@ -1494,6 +1494,14 @@ def func() -> None:
 
 class C(Self): ...  # E: Self type is only allowed in annotations within class definition
 
+[case testTypingSelfInvalidLocationsTypeParams]
+# flags: --python-version 3.12
+from typing import Self
+
+class C:
+    def bounded[T: Self](self: T) -> None: ...  # E: Self type cannot be used in a type parameter bound
+    def constrained[T: (C, Self)](self: T) -> None: ...  # E: Self type cannot be used in a type parameter constraint
+
 [case testTypingSelfInvalidArgs]
 from typing import Self, List
 

From b1f235a13e02e11ec9bcc861992a559007e81ee4 Mon Sep 17 00:00:00 2001
From: wolfgang-aura <169568318+wolfgang-aura@users.noreply.github.com>
Date: Wed, 9 Sep 2026 10:49:34 +0800
Subject: [PATCH 2/2] wip: keep PEP 695 Self test on supported runtimes

---
 test-data/unit/check-python312.test | 8 ++++++++
 test-data/unit/check-selftype.test  | 8 --------
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/test-data/unit/check-python312.test b/test-data/unit/check-python312.test
index 9d612109d5452..bb770a9f09176 100644
--- a/test-data/unit/check-python312.test
+++ b/test-data/unit/check-python312.test
@@ -1446,6 +1446,14 @@ reveal_type(F[str]().m())  # N: Revealed type is "__main__.F[builtins.str]"
 reveal_type(F[str]().mm(b'x'))  # N: Revealed type is "tuple[__main__.F[builtins.str], builtins.bytes]"
 [builtins fixtures/tuple.pyi]
 
+[case testTypingSelfInvalidLocationsTypeParams]
+# flags: --python-version 3.12
+from typing import Self
+
+class C:
+    def bounded[T: Self](self: T) -> None: ...  # E: Self type cannot be used in a type parameter bound
+    def constrained[T: (C, Self)](self: T) -> None: ...  # E: Self type cannot be used in a type parameter constraint
+
 [case testPEP695CallAlias]
 class C:
     def __init__(self, x: str) -> None: ...
diff --git a/test-data/unit/check-selftype.test b/test-data/unit/check-selftype.test
index 49d3c228d3b27..c157200352562 100644
--- a/test-data/unit/check-selftype.test
+++ b/test-data/unit/check-selftype.test
@@ -1494,14 +1494,6 @@ def func() -> None:
 
 class C(Self): ...  # E: Self type is only allowed in annotations within class definition
 
-[case testTypingSelfInvalidLocationsTypeParams]
-# flags: --python-version 3.12
-from typing import Self
-
-class C:
-    def bounded[T: Self](self: T) -> None: ...  # E: Self type cannot be used in a type parameter bound
-    def constrained[T: (C, Self)](self: T) -> None: ...  # E: Self type cannot be used in a type parameter constraint
-
 [case testTypingSelfInvalidArgs]
 from typing import Self, List