Revert "Fix callable instance variable support (#10548)" (#11571)

This reverts commit 6ab0efc.

Reverting the change since it causes a significant backward
compatibility break. Code like this previously worked as expected:

```
class C:
    def f(self, ...) -> None: pass

    g = f

C().g(...)  # Now sometimes generates an error
```

However, #10548 broke this in a subtle way (no error on definition,
it sometimes generates an error on call), and instead required the 
introduction of a ClassVar annotation for `g`, which is non-intuitive 
and error-prone. For example, some typeshed stubs use method 
aliases such as the above (e.g. stubs for `logging`), and the change 
broke those stubs. It's also arguably inconsistent, since normally 
ClassVar annotations are optional.

Any fix to the original issue should avoid breaking method aliases
such as the above. Hopefully the fix can be adjusted suitably.

The PR may have broken incremental mode somehow as well -- cached
and uncached runs sometimes produce different results. The root
cause is still unclear, however.

Author: JukkaL

Diff for: mypy/checkmember.py

@@ -532,17 +532,6 @@ def instance_alias_type(alias: TypeAlias,
     return expand_type_by_instance(tp, target)
 
 
-def is_instance_var(var: Var, info: TypeInfo) -> bool:
-    """Return if var is an instance variable according to PEP 526."""
-    return (
-        # check the type_info node is the var (not a decorated function, etc.)
-        var.name in info.names and info.names[var.name].node is var
-        and not var.is_classvar
-        # variables without annotations are treated as classvar
-        and not var.is_inferred
-    )
-
-
 def analyze_var(name: str,
                 var: Var,
                 itype: Instance,
@@ -571,12 +560,7 @@ def analyze_var(name: str,
         t = get_proper_type(expand_type_by_instance(typ, itype))
         result: Type = t
         typ = get_proper_type(typ)
-        if (
-            var.is_initialized_in_class
-            and not is_instance_var(var, info)
-            and isinstance(typ, FunctionLike)
-            and not typ.is_type_obj()
-        ):
+        if var.is_initialized_in_class and isinstance(typ, FunctionLike) and not typ.is_type_obj():
             if mx.is_lvalue:
                 if var.is_property:
                     if not var.is_settable_property:

Diff for: test-data/unit/check-dataclasses.test

@@ -1263,45 +1263,81 @@ reveal_type(A.__dataclass_fields__)  # N: Revealed type is "builtins.dict[builti
 
 [builtins fixtures/dict.pyi]
 
-[case testDataclassCallableFieldAccess]
+[case testDataclassCallableProperty]
 # flags: --python-version 3.7
 from dataclasses import dataclass
 from typing import Callable
 
 @dataclass
 class A:
-    x: Callable[[int], int]
-    y: Callable[[int], int] = lambda i: i
+    foo: Callable[[int], int]
 
-a = A(lambda i:i)
-x: int = a.x(0)
-y: str = a.y(0) # E: Incompatible types in assignment (expression has type "int", variable has type "str")
-reveal_type(a.x)  # N: Revealed type is "def (builtins.int) -> builtins.int"
-reveal_type(a.y)  # N: Revealed type is "def (builtins.int) -> builtins.int"
-reveal_type(A.y)  # N: Revealed type is "def (builtins.int) -> builtins.int"
+def my_foo(x: int) -> int:
+    return x
 
+a = A(foo=my_foo)
+a.foo(1)
+reveal_type(a.foo)  # N: Revealed type is "def (builtins.int) -> builtins.int"
+reveal_type(A.foo)  # N: Revealed type is "def (builtins.int) -> builtins.int"
+[typing fixtures/typing-medium.pyi]
 [builtins fixtures/dataclasses.pyi]
 
-[case testDataclassCallableFieldAssignment]
+[case testDataclassCallableAssignment]
 # flags: --python-version 3.7
 from dataclasses import dataclass
 from typing import Callable
 
 @dataclass
 class A:
-    x: Callable[[int], int]
+    foo: Callable[[int], int]
+
+def my_foo(x: int) -> int:
+    return x
 
-def x(i: int) -> int:
-    return i
-def x2(s: str) -> str:
-    return s
+a = A(foo=my_foo)
 
-a = A(lambda i:i)
-a.x = x
-a.x = x2 # E: Incompatible types in assignment (expression has type "Callable[[str], str]", variable has type "Callable[[int], int]")
+def another_foo(x: int) -> int:
+    return x
+
+a.foo = another_foo
+[builtins fixtures/dataclasses.pyi]
 
+[case testDataclassCallablePropertyWrongType]
+# flags: --python-version 3.7
+from dataclasses import dataclass
+from typing import Callable
+
+@dataclass
+class A:
+    foo: Callable[[int], int]
+
+def my_foo(x: int) -> str:
+    return "foo"
+
+a = A(foo=my_foo)  # E: Argument "foo" to "A" has incompatible type "Callable[[int], str]"; expected "Callable[[int], int]"
+[typing fixtures/typing-medium.pyi]
 [builtins fixtures/dataclasses.pyi]
 
+[case testDataclassCallablePropertyWrongTypeAssignment]
+# flags: --python-version 3.7
+from dataclasses import dataclass
+from typing import Callable
+
+@dataclass
+class A:
+    foo: Callable[[int], int]
+
+def my_foo(x: int) -> int:
+    return x
+
+a = A(foo=my_foo)
+
+def another_foo(x: int) -> str:
+    return "foo"
+
+a.foo = another_foo  # E: Incompatible types in assignment (expression has type "Callable[[int], str]", variable has type "Callable[[int], int]")
+[typing fixtures/typing-medium.pyi]
+[builtins fixtures/dataclasses.pyi]
 
 [case testDataclassFieldDoesNotFailOnKwargsUnpacking]
 # flags: --python-version 3.7
@@ -1351,7 +1387,6 @@ class Foo:
 reveal_type(Foo(bar=1.5))  # N: Revealed type is "__main__.Foo"
 [builtins fixtures/dataclasses.pyi]
 
-
 [case testDataclassWithSlotsArg]
 # flags: --python-version 3.10
 from dataclasses import dataclass

Diff for: test-data/unit/check-functions.test

@@ -599,51 +599,39 @@ A().f('') # E: Argument 1 to "f" of "A" has incompatible type "str"; expected "i
 
 
 [case testMethodAsDataAttribute]
-from typing import Any, Callable, ClassVar
+from typing import Any, Callable
 class B: pass
 x = None # type: Any
 class A:
-    f = x # type: ClassVar[Callable[[A], None]]
-    g = x # type: ClassVar[Callable[[A, B], None]]
+    f = x # type: Callable[[A], None]
+    g = x # type: Callable[[A, B], None]
 a = None # type: A
 a.f()
 a.g(B())
 a.f(a) # E: Too many arguments
 a.g()  # E: Too few arguments
 
 [case testMethodWithInvalidMethodAsDataAttribute]
-from typing import Any, Callable, ClassVar
+from typing import Any, Callable
 class B: pass
 x = None # type: Any
 class A:
-    f = x # type: ClassVar[Callable[[], None]]
-    g = x # type: ClassVar[Callable[[B], None]]
+    f = x # type: Callable[[], None]
+    g = x # type: Callable[[B], None]
 a = None # type: A
 a.f() # E: Attribute function "f" with type "Callable[[], None]" does not accept self argument
 a.g() # E: Invalid self argument "A" to attribute function "g" with type "Callable[[B], None]"
 
 [case testMethodWithDynamicallyTypedMethodAsDataAttribute]
-from typing import Any, Callable, ClassVar
+from typing import Any, Callable
 class B: pass
 x = None # type: Any
 class A:
-    f = x # type: ClassVar[Callable[[Any], Any]]
+    f = x # type: Callable[[Any], Any]
 a = None # type: A
 a.f()
 a.f(a) # E: Too many arguments
 
-[case testMethodWithInferredMethodAsDataAttribute]
-from typing import Any
-def m(self: "A") -> int: ...
-
-class A:
-    n = m
-
-a = A()
-reveal_type(a.n())  # N: Revealed type is "builtins.int"
-reveal_type(A.n(a))  # N: Revealed type is "builtins.int"
-A.n()  # E: Too few arguments
-
 [case testOverloadedMethodAsDataAttribute]
 from foo import *
 [file foo.pyi]
@@ -685,35 +673,35 @@ a.g(B())
 a.g(a)   # E: Argument 1 has incompatible type "A[B]"; expected "B"
 
 [case testInvalidMethodAsDataAttributeInGenericClass]
-from typing import Any, TypeVar, Generic, Callable, ClassVar
+from typing import Any, TypeVar, Generic, Callable
 t = TypeVar('t')
 class B: pass
 class C: pass
 x = None # type: Any
 class A(Generic[t]):
-    f = x # type: ClassVar[Callable[[A[B]], None]]
+    f = x # type: Callable[[A[B]], None]
 ab = None # type: A[B]
 ac = None # type: A[C]
 ab.f()
 ac.f()   # E: Invalid self argument "A[C]" to attribute function "f" with type "Callable[[A[B]], None]"
 
 [case testPartiallyTypedSelfInMethodDataAttribute]
-from typing import Any, TypeVar, Generic, Callable, ClassVar
+from typing import Any, TypeVar, Generic, Callable
 t = TypeVar('t')
 class B: pass
 class C: pass
 x = None # type: Any
 class A(Generic[t]):
-    f = x # type: ClassVar[Callable[[A], None]]
+    f = x # type: Callable[[A], None]
 ab = None # type: A[B]
 ac = None # type: A[C]
 ab.f()
 ac.f()
 
 [case testCallableDataAttribute]
-from typing import Callable, ClassVar
+from typing import Callable
 class A:
-    g = None # type: ClassVar[Callable[[A], None]]
+    g = None # type: Callable[[A], None]
     def __init__(self, f: Callable[[], None]) -> None:
         self.f = f
 a = A(None)

Diff for: test-data/unit/check-functools.test

@@ -25,12 +25,12 @@ Ord() >= 1  # E: Unsupported operand types for >= ("Ord" and "int")
 
 [case testTotalOrderingLambda]
 from functools import total_ordering
-from typing import Any, Callable, ClassVar
+from typing import Any, Callable
 
 @total_ordering
 class Ord:
-    __eq__: ClassVar[Callable[[Any, object], bool]] = lambda self, other: False
-    __lt__: ClassVar[Callable[[Any, "Ord"], bool]] = lambda self, other: False
+    __eq__: Callable[[Any, object], bool] = lambda self, other: False
+    __lt__: Callable[[Any, "Ord"], bool] = lambda self, other: False
 
 reveal_type(Ord() < Ord())  # N: Revealed type is "builtins.bool"
 reveal_type(Ord() <= Ord())  # N: Revealed type is "builtins.bool"

Diff for: test-data/unit/check-selftype.test

@@ -366,16 +366,16 @@ reveal_type(x.f)  # N: Revealed type is "builtins.int"
 [builtins fixtures/property.pyi]
 
 [case testSelfTypeProperSupertypeAttribute]
-from typing import Callable, TypeVar, ClassVar
+from typing import Callable, TypeVar
 class K: pass
 T = TypeVar('T', bound=K)
 class A(K):
     @property
     def g(self: K) -> int: return 0
     @property
     def gt(self: T) -> T: return self
-    f: ClassVar[Callable[[object], int]]
-    ft: ClassVar[Callable[[T], T]]
+    f: Callable[[object], int]
+    ft: Callable[[T], T]
 
 class B(A):
     pass
@@ -392,15 +392,15 @@ reveal_type(B().ft())  # N: Revealed type is "__main__.B*"
 [builtins fixtures/property.pyi]
 
 [case testSelfTypeProperSupertypeAttributeTuple]
-from typing import Callable, TypeVar, Tuple, ClassVar
+from typing import Callable, TypeVar, Tuple
 T = TypeVar('T')
 class A(Tuple[int, int]):
     @property
     def g(self: object) -> int: return 0
     @property
     def gt(self: T) -> T: return self
-    f: ClassVar[Callable[[object], int]]
-    ft: ClassVar[Callable[[T], T]]
+    f: Callable[[object], int]
+    ft: Callable[[T], T]
 
 class B(A):
     pass
@@ -450,7 +450,7 @@ reveal_type(X1.ft())  # N: Revealed type is "Type[__main__.X]"
 [builtins fixtures/property.pyi]
 
 [case testSelfTypeProperSupertypeAttributeGeneric]
-from typing import Callable, TypeVar, Generic, ClassVar
+from typing import Callable, TypeVar, Generic
 Q = TypeVar('Q', covariant=True)
 class K(Generic[Q]):
     q: Q
@@ -460,8 +460,8 @@ class A(K[Q]):
     def g(self: K[object]) -> int: return 0
     @property
     def gt(self: K[T]) -> T: return self.q
-    f: ClassVar[Callable[[object], int]]
-    ft: ClassVar[Callable[[T], T]]
+    f: Callable[[object], int]
+    ft: Callable[[T], T]
 
 class B(A[Q]):
     pass

Diff for: test-data/unit/check-slots.test

@@ -361,7 +361,8 @@ a.a = 1
 a.b = custom_obj
 a.c = custom_obj
 a.d = custom_obj
-a.e = custom_obj
+# TODO: Should this be allowed?
+a.e = custom_obj  # E: Cannot assign to a method
 [out]
 [builtins fixtures/tuple.pyi]
 [builtins fixtures/dict.pyi]