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Check kwargs key type as covariant #10223

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Check kwargs key type as covariant #10223

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23 changes: 9 additions & 14 deletions mypy/checkexpr.py
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Original file line number Diff line number Diff line change
Expand Up @@ -32,7 +32,7 @@
YieldFromExpr, TypedDictExpr, PromoteExpr, NewTypeExpr, NamedTupleExpr, TypeVarExpr,
TypeAliasExpr, BackquoteExpr, EnumCallExpr, TypeAlias, SymbolNode, PlaceholderNode,
ParamSpecExpr,
ARG_POS, ARG_OPT, ARG_NAMED, ARG_STAR, ARG_STAR2, LITERAL_TYPE, REVEAL_TYPE,
ARG_POS, ARG_OPT, ARG_NAMED, ARG_STAR, ARG_STAR2, COVARIANT, LITERAL_TYPE, REVEAL_TYPE,
)
from mypy.literals import literal
from mypy import nodes
Expand Down Expand Up @@ -3938,20 +3938,15 @@ def is_valid_var_arg(self, typ: Type) -> bool:
def is_valid_keyword_var_arg(self, typ: Type) -> bool:
"""Is a type valid as a **kwargs argument?"""
if self.chk.options.python_version[0] >= 3:
return is_subtype(typ, self.chk.named_generic_type(
'typing.Mapping', [self.named_type('builtins.str'),
AnyType(TypeOfAny.special_form)]))
key_type = self.named_type('builtins.str')
else:
return (
is_subtype(typ, self.chk.named_generic_type(
'typing.Mapping',
[self.named_type('builtins.str'),
AnyType(TypeOfAny.special_form)]))
or
is_subtype(typ, self.chk.named_generic_type(
'typing.Mapping',
[self.named_type('builtins.unicode'),
AnyType(TypeOfAny.special_form)])))
key_type = UnionType.make_union([
self.named_type('builtins.str'),
self.named_type('builtins.unicode')])
kwargs_type = self.chk.named_generic_type(
'typing.Mapping', [key_type, AnyType(TypeOfAny.special_form)])
kwargs_type.type.defn.type_vars[0].variance = COVARIANT
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Wouldn't this affect all uses of Mapping after this code runs?

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Ahh, you're right. Didn't realized that before.

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The fix I was thinking was something along these lines.

Suggested change
kwargs_type.type.defn.type_vars[0].variance = COVARIANT
is_subtype(typ, self.chk.named_type('typing.Mapping')) and isinstance(typ.args[0], LiteralType)

This wouldn't cover the case of Literal["a", "b"] but you can try using the try_getting_str_literals_from_type method

return is_subtype(typ, kwargs_type)

def has_member(self, typ: Type, member: str) -> bool:
"""Does type have member with the given name?"""
Expand Down
16 changes: 16 additions & 0 deletions test-data/unit/check-kwargs.test
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Expand Up @@ -339,6 +339,22 @@ f(**b)
class A: pass
[builtins fixtures/dict.pyi]

[case testPassingStringLiteralForKeywordVarArg]
from typing import Any, Dict
from typing_extensions import Literal
kw: Dict[Literal["a", "b"], Any]
def f(a, b): pass
f(**kw)
[builtins fixtures/dict.pyi]

[case tesPassingVariousLiteralsForKeywordVarArg]
from typing import Any, Dict
from typing_extensions import Literal
kw: Dict[Literal[1, "a"], Any]
def f(a, b): pass
f(**kw) # E: Keywords must be strings
[builtins fixtures/dict.pyi]

[case testPassingMappingSubclassForKeywordVarArg]
from typing import Mapping
class MappingSubclass(Mapping[str, str]): pass
Expand Down