Ignore dataclass.__replace__ LSP violations (#18464)

Refining dataclass attributes with a narrower type has historically been
accepted. Mypy shouldn't emit an LSP warning for the synthesized
`__replace__` method added in Python 3.13 either.

Users are instead encouraged to enable `--enable-error-code
mutable-override` to highlight potential issues.

Fixes #18216

Author: cdce8p

mypy/checker.py

@@ -1980,12 +1980,15 @@ def check_method_override(
         Return a list of base classes which contain an attribute with the method name.
         """
         # Check against definitions in base classes.
-        check_override_compatibility = defn.name not in (
-            "__init__",
-            "__new__",
-            "__init_subclass__",
-            "__post_init__",
-        ) and (self.options.check_untyped_defs or not defn.is_dynamic())
+        check_override_compatibility = (
+            defn.name not in ("__init__", "__new__", "__init_subclass__", "__post_init__")
+            and (self.options.check_untyped_defs or not defn.is_dynamic())
+            and (
+                # don't check override for synthesized __replace__ methods from dataclasses
+                defn.name != "__replace__"
+                or defn.info.metadata.get("dataclass_tag") is None
+            )
+        )
         found_method_base_classes: list[TypeInfo] = []
         for base in defn.info.mro[1:]:
             result = self.check_method_or_accessor_override_for_base(

test-data/unit/check-classes.test

@@ -687,6 +687,20 @@ class B(A):
     def h(cls) -> int: pass
 [builtins fixtures/classmethod.pyi]
 
+[case testOverrideReplaceMethod]
+# flags: --show-error-codes
+from typing import Optional
+from typing_extensions import Self
+class A:
+    def __replace__(self, x: Optional[str]) -> Self: pass
+
+class B(A):
+    def __replace__(self, x: str) -> Self: pass # E: \
+        # E: Argument 1 of "__replace__" is incompatible with supertype "A"; supertype defines the argument type as "Optional[str]"  [override] \
+        # 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 testAllowCovarianceInReadOnlyAttributes]
 from typing import Callable, TypeVar
 

test-data/unit/check-dataclasses.test

@@ -2527,16 +2527,29 @@ Gen(2).__replace__(x="not an int")  # E: Argument "x" to "__replace__" of "Gen"
 [builtins fixtures/tuple.pyi]
 
 [case testDunderReplaceCovariantOverride]
-# flags: --python-version 3.13
+# flags: --python-version 3.13  --enable-error-code mutable-override
 from dataclasses import dataclass
+from typing import Optional
+from typing_extensions import dataclass_transform
 
 @dataclass
 class Base:
-    a: object
+    a: Optional[int]
 
 @dataclass
-class Child(Base):  # E: Argument 1 of "__replace__" is incompatible with supertype "Base"; supertype defines the argument type as "object" \
-                    # N: This violates the Liskov substitution principle \
-                    # N: See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides
-    a: int
+class Child(Base):
+    a: int  # E: Covariant override of a mutable attribute (base class "Base" defined the type as "Optional[int]", expression has type "int")
+
+@dataclass
+class Other(Base):
+    a: str  # E: Incompatible types in assignment (expression has type "str", base class "Base" defined the type as "Optional[int]")
+
+@dataclass_transform(kw_only_default=True)
+class DCMeta(type): ...
+
+class X(metaclass=DCMeta):
+    a: Optional[int]
+
+class Y(X):
+    a: int  # E: Covariant override of a mutable attribute (base class "X" defined the type as "Optional[int]", expression has type "int")
 [builtins fixtures/tuple.pyi]