Remove TypeType exception for abstract instantiation

If A is abstract, it's weird to me that we have a difference in the
following two calls:
```
from abc import abstractmethod, ABCMeta
class A(metaclass=ABCMeta):
    @AbstractMethod
    def __init__(self, a: int) -> None:
        pass

def test_a(A_t: type[A]) -> None:
    A_t(1)
    A(1)
```

Mypy tries to then enforce soundness by preventing you from passing `A`
to a parameter of `type[A]`. But this is very unpopular, since there
are legitimate uses of `A` that have nothing to do with instantiation.
See #4717

As mentioned in
https://discuss.python.org/t/compatibility-of-protocol-class-object-with-type-t-and-type-any/48442/2
I think we should switch to disallowing instantiation of `type[Proto]` and
`type[Abstract]`.

This also makes tackling `__init__` unsoundness more tractable. If
people want unsound `__init__`, they can use `Callable[..., P]`.

Author: hauntsaninja

mypy/checkexpr.py

@@ -1668,21 +1668,14 @@ def check_callable_call(
             # An Enum() call that failed SemanticAnalyzerPass2.check_enum_call().
             return callee.ret_type, callee
 
-        if (
-            callee.is_type_obj()
-            and callee.type_object().is_protocol
-            # Exception for Type[...]
-            and not callee.from_type_type
-        ):
+        if callee.is_type_obj() and callee.type_object().is_protocol:
             self.chk.fail(
                 message_registry.CANNOT_INSTANTIATE_PROTOCOL.format(callee.type_object().name),
                 context,
             )
         elif (
             callee.is_type_obj()
             and callee.type_object().is_abstract
-            # Exception for Type[...]
-            and not callee.from_type_type
             and not callee.type_object().fallback_to_any
         ):
             type = callee.type_object()

test-data/unit/check-abstract.test

@@ -187,7 +187,7 @@ class C(B):
         pass
 
 def f(cls: Type[A]) -> A:
-    return cls()  # OK
+    return cls()  # E: Cannot instantiate abstract class "A" with abstract attribute "m"
 def g() -> A:
     return A()  # E: Cannot instantiate abstract class "A" with abstract attribute "m"
 
@@ -196,7 +196,6 @@ f(B)  # E: Only concrete class can be given where "Type[A]" is expected
 f(C)  # OK
 x: Type[B]
 f(x)  # OK
-[out]
 
 [case testAbstractTypeInADict]
 from typing import Dict, Type
@@ -229,15 +228,14 @@ class C(B):
         pass
 
 def f(cls: Type[A]) -> A:
-    return cls()  # OK
+    return cls()  # E: Cannot instantiate abstract class "A" with abstract attribute "m"
 
 Alias = A
 GoodAlias = C
 Alias()  # E: Cannot instantiate abstract class "A" with abstract attribute "m"
 GoodAlias()
 f(Alias)  # E: Only concrete class can be given where "Type[A]" is expected
 f(GoodAlias)
-[out]
 
 [case testInstantiationAbstractsInTypeForVariables]
 # flags: --no-strict-optional
@@ -253,7 +251,7 @@ class C(B):
         pass
 
 var: Type[A]
-var()
+var()  # E: Cannot instantiate abstract class "A" with abstract attribute "m"
 if int():
     var = A # E: Can only assign concrete classes to a variable of type "Type[A]"
 if int():
@@ -262,7 +260,7 @@ if int():
     var = C # OK
 
 var_old = None # type: Type[A] # Old syntax for variable annotations
-var_old()
+var_old()  # E: Cannot instantiate abstract class "A" with abstract attribute "m"
 if int():
     var_old = A # E: Can only assign concrete classes to a variable of type "Type[A]"
 if int():
@@ -278,7 +276,7 @@ class D(A):
     def __new__(cls, a=None) -> "D": ...
 if int():
     var = D # E: Can only assign concrete classes to a variable of type "Type[A]"
-[out]
+
 
 [case testInstantiationAbstractsInTypeForClassMethods]
 from typing import Type
@@ -291,13 +289,12 @@ class Logger:
 class C:
     @classmethod
     def action(cls) -> None:
-        cls() #OK for classmethods
+        cls() # E: Cannot instantiate abstract class "C" with abstract attribute "m"
         Logger.log(cls)  #OK for classmethods
     @abstractmethod
     def m(self) -> None:
         pass
 [builtins fixtures/classmethod.pyi]
-[out]
 
 [case testInstantiatingClassWithInheritedAbstractMethodAndSuppression]
 from abc import abstractmethod, ABCMeta
@@ -324,7 +321,6 @@ class A(metaclass=ABCMeta):
     @abstractmethod
     def j(self): pass
 a = A() # E: Cannot instantiate abstract class "A" with abstract attributes "a", "b", ... and "j" (7 methods suppressed)
-[out]
 
 
 -- Implementing abstract methods
@@ -1085,9 +1081,9 @@ my_abstract_types = {
 reveal_type(my_concrete_types)  # N: Revealed type is "builtins.dict[builtins.str, def () -> __main__.MyAbstractType]"
 reveal_type(my_abstract_types)  # N: Revealed type is "builtins.dict[builtins.str, def () -> __main__.MyAbstractType]"
 
-a = my_concrete_types['A']()
+a = my_concrete_types['A']()  # E: Cannot instantiate abstract class "MyAbstractType" with abstract attribute "do"
 a.do()
-b = my_concrete_types['B']()
+b = my_concrete_types['B']()  # E: Cannot instantiate abstract class "MyAbstractType" with abstract attribute "do"
 b.do()
 
 c = my_abstract_types['A']()  # E: Cannot instantiate abstract class "MyAbstractType" with abstract attribute "do"

test-data/unit/check-classes.test

@@ -1526,7 +1526,8 @@ import typing
 class C:
   @classmethod
   def foo(cls) -> None:
-      cls().bar()
+      c = cls()  # E: Cannot instantiate abstract class "C" with abstract attribute "bar"
+      c.bar()
   @abstractmethod
   def bar(self) -> None:
       pass

test-data/unit/check-functools.test

@@ -586,9 +586,9 @@ class A(ABC):
     def method(self) -> None: ...
 
 def f1(cls: type[A]) -> None:
-    cls()
-    partial_cls = partial(cls)
-    partial_cls()
+    cls()  # E: Cannot instantiate abstract class "A" with abstract attribute "method"
+    partial_cls = partial(cls)  # E: Cannot instantiate abstract class "A" with abstract attribute "method"
+    partial_cls()  # E: Cannot instantiate abstract class "A" with abstract attribute "method"
 
 def f2() -> None:
     A()  # E: Cannot instantiate abstract class "A" with abstract attribute "method"

test-data/unit/check-protocols.test

@@ -1603,7 +1603,7 @@ class C:
         pass
 
 def f(cls: Type[P]) -> P:
-    return cls()  # OK
+    return cls()  # E: Cannot instantiate protocol class "P"
 def g() -> P:
     return P()  # E: Cannot instantiate protocol class "P"
 
@@ -1625,7 +1625,7 @@ class C:
         pass
 
 def f(cls: Type[P]) -> P:
-    return cls()  # OK
+    return cls()  # E: Cannot instantiate protocol class "P"
 
 Alias = P
 GoodAlias = C
@@ -1646,14 +1646,14 @@ class C:
         pass
 
 var: Type[P]
-var()
+var()  # E: Cannot instantiate protocol class "P"
 if int():
     var = P # E: Can only assign concrete classes to a variable of type "Type[P]"
     var = B # OK
     var = C # OK
 
 var_old = None # type: Type[P] # Old syntax for variable annotations
-var_old()
+var_old()  # E: Cannot instantiate protocol class "P"
 if int():
     var_old = P # E: Can only assign concrete classes to a variable of type "Type[P]"
     var_old = B # OK
@@ -1669,7 +1669,7 @@ class Logger:
 class C(Protocol):
     @classmethod
     def action(cls) -> None:
-        cls() #OK for classmethods
+        cls() # E: Cannot instantiate protocol class "C"
         Logger.log(cls)  #OK for classmethods
 [builtins fixtures/classmethod.pyi]
 

test-data/unit/check-selftype.test

@@ -1023,7 +1023,7 @@ T = TypeVar('T', bound=HasX)
 class Meta(type):
     def do_x(cls: Type[T]) -> T:
         cls.x
-        return cls()
+        return cls()  # E: Cannot instantiate protocol class "HasX"
 
 class Good(metaclass=Meta):
     x: int