From f0fcbcec373a8eaab9cce08f6ce4eb128c13cb44 Mon Sep 17 00:00:00 2001
From: EmmanuelNiyonshuti <nemmy0257@gmail.com>
Date: Thu, 10 Sep 2026 22:04:57 +0200
Subject: [PATCH] Reject type variable whose upper bound is Self

---
 mypy/message_registry.py            | 4 ++++
 mypy/semanal.py                     | 2 ++
 test-data/unit/check-python312.test | 7 +++++++
 3 files changed, 13 insertions(+)

diff --git a/mypy/message_registry.py b/mypy/message_registry.py
index 2e40048cbb58b..25530fb9a5dee 100644
--- a/mypy/message_registry.py
+++ b/mypy/message_registry.py
@@ -361,6 +361,10 @@ def with_additional_msg(self, info: str) -> ErrorMessage:
     "TypeVar constraint type cannot be parametrized by type variables", codes.MISC
 )
 
+TYPE_VAR_GENERIC_BOUND_TYPE: Final = ErrorMessage(
+    "TypeVar upper bound can not be parametrized by type variables", codes.MISC
+)
+
 TYPE_VAR_REDECLARED_IN_NESTED_CLASS: Final = ErrorMessage(
     'Type variable "{}" is bound by an outer class', codes.VALID_TYPE
 )
diff --git a/mypy/semanal.py b/mypy/semanal.py
index 8d9b001ae7750..ce545838d5afe 100644
--- a/mypy/semanal.py
+++ b/mypy/semanal.py
@@ -1899,6 +1899,8 @@ def analyze_type_param(
                 # This and below copies special-casing for old-style type variables, that
                 # is equally necessary for new-style classes to break a vicious circle.
                 upper_bound = PlaceholderType(None, [], context.line)
+            elif has_type_vars(upper_bound):
+                self.fail(message_registry.TYPE_VAR_GENERIC_BOUND_TYPE, context)
         else:
             if type_param.kind == TYPE_VAR_TUPLE_KIND:
                 upper_bound = self.named_type("builtins.tuple", [self.object_type()])
diff --git a/test-data/unit/check-python312.test b/test-data/unit/check-python312.test
index 9d612109d5452..d42ab4c3286ad 100644
--- a/test-data/unit/check-python312.test
+++ b/test-data/unit/check-python312.test
@@ -1446,6 +1446,13 @@ 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 testPEP695TypeVariableBoundSelfType]
+from typing import Self
+
+class C:
+    def foo[T: Self](self: T) -> None: pass # E: TypeVar upper bound can not be parametrized by type variables
+[builtins fixtures/tuple.pyi]
+
 [case testPEP695CallAlias]
 class C:
     def __init__(self, x: str) -> None: ...