Fix multiple inheritance false positives in dataclasses and attrs classes

Multiple inheritance from dataclasses and attrs classes works at runtime,
so don't complain about `__match_args__` or `__attrs_attrs__` which tend
to have incompatible types in subclasses.

Fixes #12349. Fixes #12008. Fixes #12065.

Author: JukkaL

mypy/checker.py

@@ -2103,8 +2103,9 @@ class C(B, A[int]): ...  # this is unsafe because...
             self.msg.cant_override_final(name, base2.name, ctx)
         if is_final_node(first.node):
             self.check_if_final_var_override_writable(name, second.node, ctx)
-        # __slots__ and __deletable__ are special and the type can vary across class hierarchy.
-        if name in ('__slots__', '__deletable__'):
+        # Some attributes like __slots__ and __deletable__ are special, and the type can
+        # vary across class hierarchy.
+        if name in ('__slots__', '__deletable__', '__match_args__', '__attrs_attrs__'):
             ok = True
         if not ok:
             self.msg.base_class_definitions_incompatible(name, base1, base2,

mypy/plugins/attrs.py

@@ -778,7 +778,6 @@ def _add_match_args(ctx: 'mypy.plugin.ClassDefContext',
             cls=ctx.cls,
             name='__match_args__',
             typ=match_args,
-            final=True,
         )
 
 

mypy/plugins/dataclasses.py

@@ -227,7 +227,7 @@ def transform(self) -> None:
             literals: List[Type] = [LiteralType(attr.name, str_type)
                         for attr in attributes if attr.is_in_init]
             match_args_type = TupleType(literals, ctx.api.named_type("builtins.tuple"))
-            add_attribute_to_class(ctx.api, ctx.cls, "__match_args__", match_args_type, final=True)
+            add_attribute_to_class(ctx.api, ctx.cls, "__match_args__", match_args_type)
 
         self._add_dataclass_fields_magic_attribute()
 

test-data/unit/check-attr.test

@@ -1539,3 +1539,19 @@ n: NoMatchArgs
 reveal_type(n.__match_args__)  # E: "NoMatchArgs" has no attribute "__match_args__" \
                                # N: Revealed type is "Any"
 [builtins fixtures/attr.pyi]
+
+[case testAttrsMultipleInheritance]
+# flags: --python-version 3.10
+import attr
+
+@attr.s
+class A:
+    x = attr.ib(type=int)
+
+@attr.s
+class B:
+    y = attr.ib(type=int)
+
+class AB(A, B):
+    pass
+[builtins fixtures/attr.pyi]

test-data/unit/check-dataclasses.test

@@ -1536,3 +1536,19 @@ A(a=1, b=2)
 A(1)
 A(a="foo")  # E: Argument "a" to "A" has incompatible type "str"; expected "int"
 [builtins fixtures/dataclasses.pyi]
+
+[case testDataclassMultipleInheritance]
+# flags: --python-version 3.10
+from dataclasses import dataclass
+
+@dataclass
+class A:
+    prop_a: str
+
+@dataclass
+class B:
+    prop_b: bool
+
+class Derived(A, B):
+    pass
+[builtins fixtures/dataclasses.pyi]