Allow arbitrary overriding of __init_subclass__ (#2883)

Author: miedzinski

mypy/checker.py

@@ -837,8 +837,9 @@ def check_method_or_accessor_override_for_base(self, defn: FuncBase,
         """Check if method definition is compatible with a base class."""
         if base:
             name = defn.name()
-            if name not in ('__init__', '__new__'):
-                # Check method override (__init__ and __new__ are special).
+            if name not in ('__init__', '__new__', '__init_subclass__'):
+                # Check method override
+                # (__init__, __new__, __init_subclass__ are special).
                 self.check_method_override_for_base_with_name(defn, name, base)
                 if name in nodes.inplace_operator_methods:
                     # Figure out the name of the corresponding operator method.

test-data/unit/check-classes.test

@@ -303,6 +303,12 @@ class B(A):
     def g(self) -> None:
         def f(self) -> str: pass
 
+[case testOverride__init_subclass__WithDifferentSignature]
+class A:
+    def __init_subclass__(cls, x: int) -> None: pass
+class B(A):
+    def __init_subclass__(cls) -> None: pass
+
 
 -- Constructors
 -- ------------