Support metaclasses

mypy/checker.py

@@ -1433,6 +1433,8 @@ def split_around_star(self, items: List[T], star_index: int,
         return (left, star, right)
 
     def type_is_iterable(self, type: Type) -> bool:
+        if isinstance(type, CallableType) and type.is_type_obj():
+            type = type.fallback
         return (is_subtype(type, self.named_generic_type('typing.Iterable',
                                                         [AnyType()])) and
                 isinstance(type, Instance))
@@ -2184,6 +2186,10 @@ def visit_call_expr(self, e: CallExpr) -> Type:
     def visit_yield_from_expr(self, e: YieldFromExpr) -> Type:
         return self.expr_checker.visit_yield_from_expr(e)
 
+    def has_coroutine_decorator(self, t: Type) -> bool:
+        """Whether t came from a function decorated with `@coroutine`."""
+        return isinstance(t, Instance) and t.type.fullname() == 'typing.AwaitableGenerator'
+
     def visit_member_expr(self, e: MemberExpr) -> Type:
         return self.expr_checker.visit_member_expr(e)
 
@@ -2362,10 +2368,6 @@ def lookup_typeinfo(self, fullname: str) -> TypeInfo:
         sym = self.lookup_qualified(fullname)
         return cast(TypeInfo, sym.node)
 
-    def type_type(self) -> Instance:
-        """Return instance type 'type'."""
-        return self.named_type('builtins.type')
-
     def object_type(self) -> Instance:
         """Return instance type 'object'."""
         return self.named_type('builtins.object')

mypy/checkexpr.py

@@ -2099,8 +2099,7 @@ def visit_yield_from_expr(self, e: YieldFromExpr) -> Type:
         # by __iter__.
         if isinstance(subexpr_type, AnyType):
             iter_type = AnyType()
-        elif (isinstance(subexpr_type, Instance) and
-                is_subtype(subexpr_type, self.chk.named_type('typing.Iterable'))):
+        elif self.chk.type_is_iterable(subexpr_type):
             if is_async_def(subexpr_type) and not has_coroutine_decorator(return_type):
                 self.chk.msg.yield_from_invalid_operand_type(subexpr_type, e)
             iter_method_type = self.analyze_external_member_access(

mypy/checkmember.py

@@ -184,6 +184,8 @@ def analyze_member_access(name: str,
             if result:
                 return result
         fallback = builtin_type('builtins.type')
+        if item is not None:
+            fallback = item.type.metaclass_type or fallback
         return analyze_member_access(name, fallback, node, is_lvalue, is_super,
                                      is_operator, builtin_type, not_ready_callback, msg,
                                      original_type=original_type, chk=chk)
@@ -450,7 +452,7 @@ def type_object_type(info: TypeInfo, builtin_type: Callable[[str], Instance]) ->
         # Must be an invalid class definition.
         return AnyType()
     else:
-        fallback = builtin_type('builtins.type')
+        fallback = info.metaclass_type or builtin_type('builtins.type')
         if init_method.info.fullname() == 'builtins.object':
             # No non-default __init__ -> look at __new__ instead.
             new_method = info.get_method('__new__')

mypy/constraints.py

@@ -294,6 +294,8 @@ def visit_type_var(self, template: TypeVarType) -> List[Constraint]:
     def visit_instance(self, template: Instance) -> List[Constraint]:
         actual = self.actual
         res = []  # type: List[Constraint]
+        if isinstance(actual, CallableType) and actual.fallback is not None:
+            actual = actual.fallback
         if isinstance(actual, Instance):
             instance = actual
             if (self.direction == SUBTYPE_OF and

mypy/nodes.py

@@ -1946,6 +1946,27 @@ def __init__(self, names: 'SymbolTable', defn: ClassDef, module_name: str) -> No
             for vd in defn.type_vars:
                 self.type_vars.append(vd.name)
 
+    declared_metaclass = None  # type: Optional[mypy.types.Instance]
+    metaclass_type = None  # type: Optional[mypy.types.Instance]
+
+    def calculate_metaclass_type(self) -> 'Optional[mypy.types.Instance]':
+        if self.mro is None:
+            # XXX why does this happen?
+            return None
+        declared = self.declared_metaclass
+        if declared is not None and not declared.type.has_base('builtins.type'):
+            return declared
+        if self._fullname == 'builtins.type':
+            return mypy.types.Instance(self, [])
+        candidates = {s.declared_metaclass for s in self.mro} - {None}
+        for c in candidates:
+            if all(other.type in c.type.mro for other in candidates):
+                return c
+        return None
+
+    def is_metaclass(self) -> bool:
+        return self.has_base('builtins.type')
+
     def name(self) -> str:
         """Short name."""
         return self.defn.name
@@ -2060,6 +2081,8 @@ def serialize(self) -> JsonDict:
                 'type_vars': self.type_vars,
                 'bases': [b.serialize() for b in self.bases],
                 '_promote': None if self._promote is None else self._promote.serialize(),
+                'declared_metaclass': (None if self.declared_metaclass is None
+                                       else self.declared_metaclass.serialize()),
                 'tuple_type': None if self.tuple_type is None else self.tuple_type.serialize(),
                 'typeddict_type':
                     None if self.typeddict_type is None else self.typeddict_type.serialize(),
@@ -2081,6 +2104,9 @@ def deserialize(cls, data: JsonDict) -> 'TypeInfo':
         ti.bases = [mypy.types.Instance.deserialize(b) for b in data['bases']]
         ti._promote = (None if data['_promote'] is None
                        else mypy.types.Type.deserialize(data['_promote']))
+        ti.declared_metaclass = (None if data['declared_metaclass'] is None
+                                 else mypy.types.Instance.deserialize(data['declared_metaclass']))
+        ti.metaclass_type = ti.calculate_metaclass_type()
         ti.tuple_type = (None if data['tuple_type'] is None
                          else mypy.types.TupleType.deserialize(data['tuple_type']))
         ti.typeddict_type = (None if data['typeddict_type'] is None

mypy/semanal.py

@@ -905,8 +905,20 @@ def analyze_metaclass(self, defn: ClassDef) -> None:
                 self.fail("Dynamic metaclass not supported for '%s'" % defn.name, defn)
                 return
             sym = self.lookup_qualified(defn.metaclass, defn)
-            if sym is not None and not isinstance(sym.node, TypeInfo):
+            if sym is None:
+                # Probably a name error - it is already handled elsewhere
+                return
+            if not isinstance(sym.node, TypeInfo):
                 self.fail("Invalid metaclass '%s'" % defn.metaclass, defn)
+                return
+            inst = fill_typevars(sym.node)
+            assert isinstance(inst, Instance)
+            defn.info.declared_metaclass = inst
+            defn.info.metaclass_type = defn.info.calculate_metaclass_type()
+            if defn.info.metaclass_type is None:
+                # Inconsistency may happen due to multiple baseclasses even in classes that
+                # do not declare explicit metaclass, but it's harder to catch at this stage
+                self.fail("Inconsistent metaclass structure for '%s'" % defn.name, defn)
 
     def object_type(self) -> Instance:
         return self.named_type('__builtins__.object')

mypy/types.py

@@ -643,7 +643,8 @@ def copy_modified(self,
         )
 
     def is_type_obj(self) -> bool:
-        return self.fallback.type is not None and self.fallback.type.fullname() == 'builtins.type'
+        t = self.fallback.type
+        return t is not None and t.is_metaclass()
 
     def is_concrete_type_obj(self) -> bool:
         return self.is_type_obj() and self.is_classmethod_class

test-data/unit/check-classes.test

@@ -2759,3 +2759,50 @@ class B(A):
 class C(B):
     x = ''
 [out]
+
+[case testInvalidMetaclassStructure]
+class X(type): pass
+class Y(type): pass
+class A(metaclass=X): pass
+class B(A, metaclass=Y): pass  # E: Inconsistent metaclass structure for 'B'
+
+[case testMetaclassNoTypeReveal]
+class M:
+    x = 0  # type: int
+
+class A(metaclass=M): pass
+
+reveal_type(A.x)  # E: Revealed type is 'builtins.int'
+
+[case testMetaclassTypeReveal]
+from typing import Type
+class M(type):
+    x = 0  # type: int
+
+class A(metaclass=M): pass
+
+reveal_type(A.x)  # E: Revealed type is 'builtins.int'
+
+def f(TA: Type[A]):
+    reveal_type(TA)  # E: Revealed type is 'Type[__main__.A]'
+    reveal_type(TA.x)  # E: Revealed type is 'builtins.int'
+
+[case testMetaclassIterable]
+from typing import Iterable, Iterator
+
+class BadMeta(type):
+    def __iter__(self) -> Iterator[int]: yield 1
+
+class Bad(metaclass=BadMeta): pass
+
+for _ in Bad: pass  # E: Iterable expected
+
+class GoodMeta(type, Iterable[int]):
+    def __iter__(self) -> Iterator[int]: yield 1
+
+class Good(metaclass=GoodMeta): pass
+for _ in Good: pass
+reveal_type(list(Good))  # E: Revealed type is 'builtins.list[builtins.int*]'
+
+[builtins fixtures/list.pyi]
+

test-data/unit/lib-stub/abc.pyi

@@ -1,3 +1,3 @@
-class ABCMeta: pass
+class ABCMeta(type): pass
 abstractmethod = object()
 abstractproperty = object()