Fix __new__ and __init__ precedence

Fixes python#5647

See also python#5642

Author: hauntsaninja

mypy/checkmember.py

@@ -1329,15 +1329,18 @@ def type_object_type(info: TypeInfo, named_type: Callable[[str], Instance]) -> P
     """
 
     # We take the type from whichever of __init__ and __new__ is first
-    # in the MRO, preferring __init__ if there is a tie.
+    # in the MRO, preferring __new__ if there is a tie.
     init_method = info.get("__init__")
     new_method = info.get("__new__")
     if not init_method or not is_valid_constructor(init_method.node):
         # Must be an invalid class definition.
         return AnyType(TypeOfAny.from_error)
     # There *should* always be a __new__ method except the test stubs
-    # lack it, so just copy init_method in that situation
-    new_method = new_method or init_method
+    # lack it, so just copy builtin's init in that situation
+    if new_method is None:
+        new_method = named_type("builtins.object").type.get("__init__")
+        if not new_method:
+            return AnyType(TypeOfAny.from_error)
     if not is_valid_constructor(new_method.node):
         # Must be an invalid class definition.
         return AnyType(TypeOfAny.from_error)
@@ -1371,12 +1374,13 @@ def type_object_type(info: TypeInfo, named_type: Callable[[str], Instance]) -> P
                     fallback=named_type("builtins.function"),
                 )
                 return class_callable(sig, info, fallback, None, is_new=False)
-
-        # Otherwise prefer __init__ in a tie. It isn't clear that this
-        # is the right thing, but __new__ caused problems with
-        # typeshed (#5647).
-        method = init_method.node
-        is_new = False
+        if init_method.node.info.fullname == "builtins.dict":
+            # dict.__new__ in typeshed is pretty unhelpful
+            method = init_method.node
+            is_new = False
+        else:
+            method = new_method.node
+            is_new = True
     # Construct callable type based on signature of __init__. Adjust
     # return type and insert type arguments.
     if isinstance(method, FuncBase):

test-data/unit/check-classes.test

@@ -6324,7 +6324,7 @@ class A:
     def __init__(self, x: int) -> None:
         pass
 
-reveal_type(A)  # N: Revealed type is "def (x: builtins.int) -> __main__.A"
+reveal_type(A)  # N: Revealed type is "def (*args: Any) -> __main__.A"
 [builtins fixtures/tuple.pyi]
 
 [case testCyclicDecorator]
@@ -7883,7 +7883,7 @@ if object():
 if object():
     reveal_type(B())  # N: Revealed type is "Never"
 if object():
-    reveal_type(C())  # N: Revealed type is "Never"
+    reveal_type(C())  # N: Revealed type is "__main__.C"
 if object():
     reveal_type(D())  # N: Revealed type is "Never"
 
@@ -7933,7 +7933,7 @@ if object():
 reveal_type(B(1))  # N: Revealed type is "__main__.B"
 
 if object():
-    reveal_type(C())  # N: Revealed type is "Never"
+    reveal_type(C())  # N: Revealed type is "__main__.C"
 reveal_type(C(1))  # N: Revealed type is "__main__.C"
 
 if object():

test-data/unit/fixtures/object_hashable.pyi

@@ -1,4 +1,5 @@
 class object:
+    def __init__(self) -> None: ...
     def __hash__(self) -> int: ...
 
 class type: ...