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[red-knot] Simplify and generalize Type::is_subtype_of a little bit #15622

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[red-knot] Simplify and generalize Type::is_subtype_of a little bit #15622

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31 changes: 11 additions & 20 deletions crates/red_knot_python_semantic/src/types.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -964,33 +964,24 @@ impl<'db> Type<'db> {
// `Literal[str]` is a subtype of `type` because the `str` class object is an instance of its metaclass `type`.
// `Literal[abc.ABC]` is a subtype of `abc.ABCMeta` because the `abc.ABC` class object
// is an instance of its metaclass `abc.ABCMeta`.
(
Type::ClassLiteral(ClassLiteralType { class: self_class }),
Type::Instance(InstanceType {
class: target_class,
}),
) => self_class.is_instance_of(db, target_class),
(Type::ClassLiteral(ClassLiteralType { class }), _) => class
.metaclass(db)
.to_instance(db)
.is_subtype_of(db, target),

// `type[str]` (== `SubclassOf("str")` in red-knot) describes all possible runtime subclasses
// of the class object `str`. It is a subtype of `type` (== `Instance("type")`) because `str`
// is an instance of `type`, and so all possible subclasses of `str` will also be instances of `type`.
//
// Similarly `type[enum.Enum]` is a subtype of `enum.EnumMeta` because `enum.Enum`
// is an instance of `enum.EnumMeta`.
(
Type::SubclassOf(subclass_of_ty),
Type::Instance(InstanceType {
class: target_class,
}),
) => subclass_of_ty
.subclass_of()
.into_class()
.is_some_and(|subclass_class| subclass_class.is_instance_of(db, target_class)),

// Other than the cases enumerated above, `type[]` and class-literal types just delegate to `Instance("type")`
(Type::SubclassOf(_) | Type::ClassLiteral(_), _) => {
KnownClass::Type.to_instance(db).is_subtype_of(db, target)
}
(Type::SubclassOf(subclass_of_ty), _) => match subclass_of_ty.subclass_of() {
ClassBase::Class(class) => class
.metaclass(db)
.to_instance(db)
.is_subtype_of(db, target),
ClassBase::Dynamic(_) => KnownClass::Type.to_instance(db).is_subtype_of(db, target),
},

// For example: `Type::KnownInstance(KnownInstanceType::Type)` is a subtype of `Type::Instance(_SpecialForm)`,
// because `Type::KnownInstance(KnownInstanceType::Type)` is a set with exactly one runtime value in it
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