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Fix format checking for Unions with alias with custom format #12044

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Fix format checking for Unions with alias with custom format #12044

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b5d05a4
Fix format checking for unions with alias with custom format
kreathon Jan 23, 2022
c20f7f0
Fix flake8 issue
kreathon Jan 23, 2022
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13 changes: 8 additions & 5 deletions mypy/checkstrformat.py
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Original file line number Diff line number Diff line change
Expand Up @@ -18,8 +18,9 @@
from typing_extensions import Final, TYPE_CHECKING, TypeAlias as _TypeAlias

from mypy.types import (
Type, AnyType, TupleType, Instance, UnionType, TypeOfAny, get_proper_type, TypeVarType,
LiteralType, get_proper_types
Type, AnyType, TupleType, Instance, UnionType, TypeOfAny, get_proper_type,
TypeVarType,
LiteralType, flatten_nested_unions
)
from mypy.nodes import (
StrExpr, BytesExpr, UnicodeExpr, TupleExpr, DictExpr, Context, Expression, StarExpr, CallExpr,
Expand Down Expand Up @@ -353,9 +354,11 @@ def check_specs_in_format_call(self, call: CallExpr,
if expected_type is None:
continue

a_type = get_proper_type(actual_type)
actual_items = (get_proper_types(a_type.items) if isinstance(a_type, UnionType)
else [a_type])
p_type = get_proper_type(actual_type)
if isinstance(p_type, UnionType):
actual_items = flatten_nested_unions(p_type.items, handle_type_alias_type=True)
else:
actual_items = [p_type]
for a_type in actual_items:
if custom_special_method(a_type, '__format__'):
continue
Expand Down
13 changes: 13 additions & 0 deletions test-data/unit/check-formatting.test
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Expand Up @@ -522,6 +522,19 @@ class D(bytes):
'{}'.format(D())
[builtins fixtures/primitives.pyi]

[case testFormatCallFormatTypesUnionAliasWithCustomFormat]
from typing import Union

class Date:
def __format__(self, spec: str) -> str: ...

S = Union[str, bytes, Date]
s: Union[int, S]

'{}'.format(s) # E: On Python 3 formatting "b'abc'" with "{}" produces "b'abc'", not "abc"; use "{!r}" if this is desired behavior
f'{s}' # E: On Python 3 formatting "b'abc'" with "{}" produces "b'abc'", not "abc"; use "{!r}" if this is desired behavior
[builtins fixtures/primitives.pyi]

[case testFormatCallFormatTypesBytesNotPy2]
# flags: --py2
from typing import Union, TypeVar, NewType, Generic
Expand Down