Fix handling of non-method callable attribute (python#3227)

1. Reverse subtyping check
2. For classmethod, fallback on the argument instead of on the parameter
3. Mimic dispatch better: meet original_type with static class
4. Better error message

Author: elazarg

mypy/checkmember.py

@@ -20,6 +20,8 @@
 from mypy.plugin import Plugin, AttributeContext
 from mypy import messages
 from mypy import subtypes
+from mypy import meet
+
 MYPY = False
 if MYPY:  # import for forward declaration only
     import mypy.checker
@@ -314,7 +316,9 @@ def analyze_var(name: str, var: Var, itype: Instance, info: TypeInfo, node: Cont
                 # methods: the former to the instance, the latter to the
                 # class.
                 functype = t
-                check_method_type(functype, itype, var.is_classmethod, node, msg)
+                # Use meet to simulate dispatch - e.g. reduce Union[A, B] to A on dispatch to A
+                dispatched_type = meet.meet_types(original_type, itype)
+                check_self_arg(functype, dispatched_type, var.is_classmethod, node, name, msg)
                 signature = bind_self(functype, original_type, var.is_classmethod)
                 if var.is_property:
                     # A property cannot have an overloaded type => the cast
@@ -370,33 +374,22 @@ def lookup_member_var_or_accessor(info: TypeInfo, name: str,
         return None
 
 
-def check_method_type(functype: FunctionLike, itype: Instance, is_classmethod: bool,
-                      context: Context, msg: MessageBuilder) -> None:
+def check_self_arg(functype: FunctionLike, original_type: Type, is_classmethod: bool,
+                   context: Context, name: str, msg: MessageBuilder) -> None:
+    """Check that the the most precise type of the self argument is compatible
+    with the declared type of each of the overloads.
+    """
     for item in functype.items():
         if not item.arg_types or item.arg_kinds[0] not in (ARG_POS, ARG_STAR):
             # No positional first (self) argument (*args is okay).
-            msg.invalid_method_type(item, context)
-        elif not is_classmethod:
-            # Check that self argument has type 'Any' or valid instance type.
-            selfarg = item.arg_types[0]
-            # If this is a method of a tuple class, correct for the fact that
-            # we passed to typ.fallback in analyze_member_access. See #1432.
-            if isinstance(selfarg, TupleType):
-                selfarg = selfarg.fallback
-            if not subtypes.is_subtype(selfarg, itype):
-                msg.invalid_method_type(item, context)
+            msg.fail('Attribute function with type %s does not accept self argument'
+                     % msg.format(item), context)
         else:
-            # Check that cls argument has type 'Any' or valid class type.
-            # (This is sufficient for the current treatment of @classmethod,
-            # but probably needs to be revisited when we implement Type[C]
-            # or advanced variants of it like Type[<args>, C].)
-            clsarg = item.arg_types[0]
-            if isinstance(clsarg, CallableType) and clsarg.is_type_obj():
-                if not subtypes.is_equivalent(clsarg.ret_type, itype):
-                    msg.invalid_class_method_type(item, context)
-            else:
-                if not subtypes.is_equivalent(clsarg, AnyType(TypeOfAny.special_form)):
-                    msg.invalid_class_method_type(item, context)
+            selfarg = item.arg_types[0]
+            if is_classmethod:
+                original_type = TypeType.make_normalized(original_type)
+            if not subtypes.is_subtype(original_type, erase_to_bound(selfarg)):
+                msg.invalid_method_type(name, original_type, item, is_classmethod, context)
 
 
 def analyze_class_attribute_access(itype: Instance,

mypy/messages.py

@@ -856,11 +856,11 @@ def cannot_determine_type(self, name: str, context: Context) -> None:
     def cannot_determine_type_in_base(self, name: str, base: str, context: Context) -> None:
         self.fail("Cannot determine type of '%s' in base class '%s'" % (name, base), context)
 
-    def invalid_method_type(self, sig: CallableType, context: Context) -> None:
-        self.fail('Invalid method type', context)
-
-    def invalid_class_method_type(self, sig: CallableType, context: Context) -> None:
-        self.fail('Invalid class method type', context)
+    def invalid_method_type(self, name: str, arg: Type, sig: CallableType, is_classmethod: bool,
+                            context: Context) -> None:
+        kind = 'class attribute function' if is_classmethod else 'attribute function'
+        self.fail('Invalid self argument %s to %s "%s" with type %s'
+                  % (self.format(arg), kind, name, self.format(sig)), context)
 
     def incompatible_conditional_function_def(self, defn: FuncDef) -> None:
         self.fail('All conditional function variants must have identical '

test-data/unit/check-classes.test

@@ -2105,7 +2105,7 @@ class B:
     a = A
     bad = lambda: 42
 
-B().bad() # E: Invalid method type
+B().bad() # E: Attribute function with type "Callable[[], int]" does not accept self argument
 reveal_type(B.a) # E: Revealed type is 'def () -> __main__.A'
 reveal_type(B().a) # E: Revealed type is 'def () -> __main__.A'
 reveal_type(B().a()) # E: Revealed type is '__main__.A'

test-data/unit/check-functions.test

@@ -507,8 +507,8 @@ class A:
     f = x # type: Callable[[], None]
     g = x # type: Callable[[B], None]
 a = None # type: A
-a.f() # E: Invalid method type
-a.g() # E: Invalid method type
+a.f() # E: Attribute function 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
@@ -568,7 +568,7 @@ class A(Generic[t]):
 ab = None # type: A[B]
 ac = None # type: A[C]
 ab.f()
-ac.f()   # E: Invalid method type
+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

test-data/unit/check-selftype.test

@@ -354,16 +354,21 @@ class E:
 [case testSelfTypeProperty]
 from typing import TypeVar
 
-T = TypeVar('T', bound='A')
+Q = TypeVar('Q')
+T = TypeVar('T', bound='X')
 
-class A:
+class X:
     @property
-    def member(self: T) -> T:
-        pass
+    def __members__(self: Q) -> Q: return self
+
+class A(X):
+    @property
+    def member(self: T) -> T: return self
 
 class B(A):
     pass
 
+reveal_type(X().__members__)  # E: Revealed type is '__main__.X*'
 reveal_type(A().member)  # E: Revealed type is '__main__.A*'
 reveal_type(B().member)  # E: Revealed type is '__main__.B*'
 
@@ -376,3 +381,21 @@ class A:
     # def g(self: None) -> None: ... see in check-python2.test
 [out]
 main:3: error: Self argument missing for a non-static method (or an invalid type for self)
+
+[case testUnionPropertyField]
+from typing import Union
+
+class A:
+    x: int
+
+class B:
+    @property
+    def x(self) -> int: return 1
+
+class C:
+    @property
+    def x(self) -> int: return 1
+
+ab: Union[A, B, C]
+reveal_type(ab.x)  # E: Revealed type is 'builtins.int'
+[builtins fixtures/property.pyi]