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[ty] Normalize single-member enums to their instance type #19502

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Merged
sharkdp merged 2 commits into from
Jul 23, 2025
Merged

[ty] Normalize single-member enums to their instance type #19502

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ff4468c
[ty] Normalize single-member enums to their instance type
sharkdp Jul 23, 2025
68c9569
Add single-member enum variant for property tests
sharkdp Jul 23, 2025
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12 changes: 11 additions & 1 deletion crates/ty_python_semantic/resources/mdtest/type_properties/is_equivalent_to.md
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@ materializations of `B`, and all materializations of `B` are also materializatio
### Fully static

```py
from typing_extensions import Literal, LiteralString, Never
from typing_extensions import Literal, LiteralString, Protocol, Never
from ty_extensions import Unknown, is_equivalent_to, static_assert, TypeOf, AlwaysTruthy, AlwaysFalsy
from enum import Enum

Expand Down Expand Up @@ -43,6 +43,16 @@ static_assert(is_equivalent_to(Literal[Single.VALUE], Single))
static_assert(is_equivalent_to(Single, Literal[Single.VALUE]))
static_assert(is_equivalent_to(Literal[Single.VALUE], Literal[Single.VALUE]))

static_assert(is_equivalent_to(tuple[Single] | int | str, str | int | tuple[Literal[Single.VALUE]]))

class Protocol1(Protocol):
a: Single

class Protocol2(Protocol):
a: Literal[Single.VALUE]

static_assert(is_equivalent_to(Protocol1, Protocol2))

static_assert(is_equivalent_to(Never, Never))
static_assert(is_equivalent_to(AlwaysTruthy, AlwaysTruthy))
static_assert(is_equivalent_to(AlwaysFalsy, AlwaysFalsy))
Expand Down
6 changes: 6 additions & 0 deletions crates/ty_python_semantic/src/types.rs
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Expand Up @@ -1062,6 +1062,12 @@ impl<'db> Type<'db> {
type_is.with_type(db, type_is.return_type(db).normalized_impl(db, v))
}),
Type::Dynamic(dynamic) => Type::Dynamic(dynamic.normalized()),
Type::EnumLiteral(enum_literal)
if is_single_member_enum(db, enum_literal.enum_class(db)) =>
{
// Always normalize single-member enums to their class instance (`Literal[Single.VALUE]` => `Single`)
enum_literal.enum_class_instance(db)
}
Comment on lines +1065 to +1070
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@sharkdp sharkdp Jul 23, 2025

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I chose this direction, because the other seems more costly in terms of performance: If we wanted to normalize Single => Literal[Single.VALUE], we would have to check every nominal instance type, to see if it's an enum — which requires a MRO traversal.

Type::LiteralString
| Type::AlwaysFalsy
| Type::AlwaysTruthy
Expand Down
13 changes: 13 additions & 0 deletions crates/ty_python_semantic/src/types/property_tests/type_generation.rs
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@@ -1,5 +1,6 @@
use crate::db::tests::TestDb;
use crate::place::{builtins_symbol, known_module_symbol};
use crate::types::enums::is_single_member_enum;
use crate::types::tuple::TupleType;
use crate::types::{
BoundMethodType, CallableType, EnumLiteralType, IntersectionBuilder, KnownClass, Parameter,
Expand Down Expand Up @@ -27,6 +28,8 @@ pub(crate) enum Ty {
BytesLiteral(&'static str),
// An enum literal variant, using `uuid.SafeUUID` as base
EnumLiteral(&'static str),
// A single-member enum literal, using `dataclasses.MISSING`
SingleMemberEnumLiteral,
// BuiltinInstance("str") corresponds to an instance of the builtin `str` class
BuiltinInstance(&'static str),
/// Members of the `abc` stdlib module
Expand Down Expand Up @@ -145,6 +148,15 @@ impl Ty {
.expect_class_literal(),
Name::new(name),
)),
Ty::SingleMemberEnumLiteral => {
let ty = known_module_symbol(db, KnownModule::Dataclasses, "MISSING")
.place
.expect_type();
debug_assert!(
matches!(ty, Type::NominalInstance(instance) if is_single_member_enum(db, instance.class.class_literal(db).0))
);
ty
}
Ty::BuiltinInstance(s) => builtins_symbol(db, s)
.place
.expect_type()
Expand Down Expand Up @@ -265,6 +277,7 @@ fn arbitrary_core_type(g: &mut Gen, fully_static: bool) -> Ty {
Ty::EnumLiteral("safe"),
Ty::EnumLiteral("unsafe"),
Ty::EnumLiteral("unknown"),
Ty::SingleMemberEnumLiteral,
Ty::KnownClassInstance(KnownClass::Object),
Ty::KnownClassInstance(KnownClass::Str),
Ty::KnownClassInstance(KnownClass::Int),
Expand Down
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