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Do not support metaclasses not inheriting from type #2820

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Merged
merged 3 commits into from
Feb 7, 2017
Merged

Do not support metaclasses not inheriting from type #2820

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d787d5f
do not support classes not subclassing type
elazarg Feb 7, 2017
e82286b
add test for indirect type subclass
elazarg Feb 7, 2017
e31394b
Merge branch 'master' into metaclass_subclass_type
elazarg Feb 7, 2017
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2 changes: 1 addition & 1 deletion mypy/nodes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2024,7 +2024,7 @@ def calculate_metaclass_type(self) -> 'Optional[mypy.types.Instance]':
return None

def is_metaclass(self) -> bool:
return self.has_base('builtins.type')
return self.has_base('builtins.type') or self.fullname() == 'abc.ABCMeta'

def _calculate_is_enum(self) -> bool:
"""
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3 changes: 3 additions & 0 deletions mypy/semanal.py
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Expand Up @@ -966,6 +966,9 @@ def analyze_metaclass(self, defn: ClassDef) -> None:
if not isinstance(sym.node, TypeInfo) or sym.node.tuple_type is not None:
self.fail("Invalid metaclass '%s'" % defn.metaclass, defn)
return
if not sym.node.is_metaclass():
self.fail("Metaclasses not inheriting from 'type' are not supported", defn)
return
inst = fill_typevars(sym.node)
assert isinstance(inst, Instance)
defn.info.declared_metaclass = inst
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14 changes: 11 additions & 3 deletions test-data/unit/check-classes.test
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Expand Up @@ -2770,9 +2770,9 @@ class B(A, metaclass=Y): pass # E: Inconsistent metaclass structure for 'B'
class M:
x = 0 # type: int

class A(metaclass=M): pass
class A(metaclass=M): pass # E: Metaclasses not inheriting from 'type' are not supported

reveal_type(A.x) # E: Revealed type is 'builtins.int'
A.x # E: "A" has no attribute "x"
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@ilevkivskyi ilevkivskyi Feb 7, 2017 •
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I would add a test that checks that "indirect" inheritance works, like:

class M1(type):
    x = 0
class M2(M1): pass
class C(metaclass=M2):
    pass
reveal_type(C.x) # E: Revealed type is 'builtins.int'

Otherwise LGTM.


[case testMetaclassTypeReveal]
from typing import Type
Expand All @@ -2785,6 +2785,14 @@ 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 testSubclassMetaclass]
class M1(type):
x = 0
class M2(M1): pass
class C(metaclass=M2):
pass
reveal_type(C.x) # E: Revealed type is 'builtins.int'

[case testMetaclassSubclass]
from typing import Type
class M(type):
Expand Down Expand Up @@ -2822,4 +2830,4 @@ from typing import Tuple
class M(Tuple[int]): pass
class C(metaclass=M): pass # E: Invalid metaclass 'M'

[builtins fixtures/tuple.pyi]
[builtins fixtures/tuple.pyi]