From a688d17c7b33ca0cc6205a87dd350bd4927db27c Mon Sep 17 00:00:00 2001
From: STerliakov <terlya.stas@gmail.com>
Date: Fri, 7 Nov 2025 18:33:55 +0100
Subject: [PATCH 1/2] Handle decorated overrides

---
 mypy/checker.py                   |  7 ++++-
 test-data/unit/check-classes.test | 52 +++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/mypy/checker.py b/mypy/checker.py
index 9f8299e6805d..4a40ef5f9138 100644
--- a/mypy/checker.py
+++ b/mypy/checker.py
@@ -2578,7 +2578,12 @@ def erase_override(t: Type) -> Type:
                         continue
                     if not is_subtype(original_arg_type, erase_override(override_arg_type)):
                         context: Context = node
-                        if isinstance(node, FuncDef) and not node.is_property:
+                        if (
+                            isinstance(node, FuncDef)
+                            and not node.is_property
+                            and not node.is_decorated
+                        ):
+                            # If there's any decorator, we can no longer map arguments 1:1 reliably.
                             arg_node = node.arguments[i + override.bound()]
                             if arg_node.line != -1:
                                 context = arg_node
diff --git a/test-data/unit/check-classes.test b/test-data/unit/check-classes.test
index c0b1114db512..0e9d6357af1a 100644
--- a/test-data/unit/check-classes.test
+++ b/test-data/unit/check-classes.test
@@ -585,6 +585,58 @@ class B(A):
     @dec
     def f(self) -> int: pass
 
+[case testOverrideWithDecoratorReturningCallable]
+from typing import Any, Callable, TypeVar
+
+class Base:
+    def get(self, a: str) -> None: ...
+
+def dec(fn: Any) -> Callable[[Any, int], None]: ...
+
+class Derived(Base):
+    @dec
+    def get(self) -> None: ...  # E: Argument 1 of "get" is incompatible with supertype "Base"; supertype defines the argument type as "str" \
+                                # N: This violates the Liskov substitution principle \
+                                # N: See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides
+[builtins fixtures/tuple.pyi]
+
+[case testOverrideWithDecoratorReturningCallable2]
+# flags: --pretty
+from typing import Any, Callable, TypeVar
+
+_C = TypeVar("_C", bound=Callable[..., Any])
+
+def infer_signature(f: _C) -> Callable[[Any], _C]: ...
+
+class Base:
+    def get(self, a: str, b: str, c: str) -> None: ...
+    def post(self, a: str, b: str) -> None: ...
+
+# Third argument incompatible
+def get(self, a: str, b: str, c: int) -> None: ...
+
+# Second argument incompatible - still should not map to **kwargs
+def post(self, a: str, b: int) -> None: ...
+
+class Derived(Base):
+    @infer_signature(get)
+    def get(self, *args: Any, **kwargs: Any) -> None: ...
+
+    @infer_signature(post)
+    def post(self, *args: Any, **kwargs: Any) -> None: ...
+[builtins fixtures/tuple.pyi]
+[out]
+main:20: error: Argument 3 of "get" is incompatible with supertype "Base"; supertype defines the argument type as "str"
+        def get(self, *args: Any, **kwargs: Any) -> None: ...
+        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+main:20: note: This violates the Liskov substitution principle
+main:20: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides
+main:23: error: Argument 2 of "post" is incompatible with supertype "Base"; supertype defines the argument type as "str"
+        def post(self, *args: Any, **kwargs: Any) -> None: ...
+        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+main:23: note: This violates the Liskov substitution principle
+main:23: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides
+
 [case testOverrideWithDecoratorReturningInstance]
 def dec(f) -> str: pass
 

From 93f53dad74b00d24d243515018324fb7f10ecd5b Mon Sep 17 00:00:00 2001
From: STerliakov <terlya.stas@gmail.com>
Date: Fri, 7 Nov 2025 18:51:28 +0100
Subject: [PATCH 2/2] Allow trivial decorators

---
 mypy/checker.py | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mypy/checker.py b/mypy/checker.py
index 4a40ef5f9138..07f5c520de95 100644
--- a/mypy/checker.py
+++ b/mypy/checker.py
@@ -2581,7 +2581,13 @@ def erase_override(t: Type) -> Type:
                         if (
                             isinstance(node, FuncDef)
                             and not node.is_property
-                            and not node.is_decorated
+                            and (
+                                not node.is_decorated  # fast path
+                                # allow trivial decorators like @classmethod and @override
+                                or not (sym := node.info.get(node.name))
+                                or not isinstance(sym.node, Decorator)
+                                or not sym.node.decorators
+                            )
                         ):
                             # If there's any decorator, we can no longer map arguments 1:1 reliably.
                             arg_node = node.arguments[i + override.bound()]