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Fix joining a function against metaclass-using object constructors #13648

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merged 2 commits into from
Sep 25, 2022
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Fix joining a function against metaclass-using object constructors #13648

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24d8733
Fix joining a function against metaclass-using object constructors
Michael0x2a Sep 12, 2022
77bf649
Respond to code review: simplify tests
Michael0x2a Sep 25, 2022
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15 changes: 8 additions & 7 deletions mypy/join.py
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Original file line number Diff line number Diff line change
Expand Up @@ -559,10 +559,10 @@ def join_similar_callables(t: CallableType, s: CallableType) -> CallableType:
arg_types: list[Type] = []
for i in range(len(t.arg_types)):
arg_types.append(meet_types(t.arg_types[i], s.arg_types[i]))
# TODO in combine_similar_callables also applies here (names and kinds)
# The fallback type can be either 'function' or 'type'. The result should have 'type' as
# fallback only if both operands have it as 'type'.
if t.fallback.type.fullname != "builtins.type":
# TODO in combine_similar_callables also applies here (names and kinds; user metaclasses)
# The fallback type can be either 'function', 'type', or some user-provided metaclass.
# The result should always use 'function' as a fallback if either operands are using it.
if t.fallback.type.fullname == "builtins.function":
fallback = t.fallback
else:
fallback = s.fallback
Expand All @@ -580,9 +580,10 @@ def combine_similar_callables(t: CallableType, s: CallableType) -> CallableType:
for i in range(len(t.arg_types)):
arg_types.append(join_types(t.arg_types[i], s.arg_types[i]))
# TODO kinds and argument names
# The fallback type can be either 'function' or 'type'. The result should have 'type' as
# fallback only if both operands have it as 'type'.
if t.fallback.type.fullname != "builtins.type":
# TODO what should happen if one fallback is 'type' and the other is a user-provided metaclass?
# The fallback type can be either 'function', 'type', or some user-provided metaclass.
# The result should always use 'function' as a fallback if either operands are using it.
if t.fallback.type.fullname == "builtins.function":
fallback = t.fallback
else:
fallback = s.fallback
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17 changes: 17 additions & 0 deletions test-data/unit/check-classes.test
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Original file line number Diff line number Diff line change
Expand Up @@ -865,6 +865,23 @@ class C(B): pass
class D(C): pass
class D2(C): pass

[case testConstructorJoinsWithCustomMetaclass]
# flags: --strict-optional
from typing import TypeVar
import abc

def func() -> None: pass
class NormalClass: pass
class WithMetaclass(metaclass=abc.ABCMeta): pass

T = TypeVar('T')
def join(x: T, y: T) -> T: pass

f1 = join(func, WithMetaclass)
reveal_type(f1()) # N: Revealed type is "Union[__main__.WithMetaclass, None]"

f2 = join(WithMetaclass, func)
reveal_type(f2()) # N: Revealed type is "Union[__main__.WithMetaclass, None]"

-- Attribute access in class body
-- ------------------------------
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