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[ty] Simplify Any | (Any & T) to Any #20593

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Merged
merged 1 commit into from
Sep 26, 2025
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[ty] Simplify Any | (Any & T) to Any #20593

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5 changes: 5 additions & 0 deletions 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 @@ -133,6 +133,11 @@ class Single(Enum):
VALUE = 1

static_assert(is_equivalent_to(P | Q | Single, Literal[Single.VALUE] | Q | P))

static_assert(is_equivalent_to(Any, Any | Intersection[Any, str]))
static_assert(is_equivalent_to(Any, Intersection[str, Any] | Any))
static_assert(is_equivalent_to(Any, Any | Intersection[Any, Not[None]]))
static_assert(is_equivalent_to(Any, Intersection[Not[None], Any] | Any))
```

## Tuples
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7 changes: 7 additions & 0 deletions crates/ty_python_semantic/src/types.rs
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Expand Up @@ -1050,6 +1050,13 @@ impl<'db> Type<'db> {
}
}

pub(crate) const fn into_intersection(self) -> Option<IntersectionType<'db>> {
match self {
Type::Intersection(intersection_type) => Some(intersection_type),
_ => None,
}
}

#[cfg(test)]
#[track_caller]
pub(crate) fn expect_union(self) -> UnionType<'db> {
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9 changes: 8 additions & 1 deletion crates/ty_python_semantic/src/types/builder.rs
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Expand Up @@ -504,9 +504,16 @@ impl<'db> UnionBuilder<'db> {
if should_simplify_full && !matches!(element_type, Type::TypeAlias(_)) {
if ty.is_equivalent_to(self.db, element_type)
|| ty.is_subtype_of(self.db, element_type)
|| ty.into_intersection().is_some_and(|intersection| {
intersection.positive(self.db).contains(&element_type)
})
Comment on lines 505 to +509
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@AlexWaygood AlexWaygood Sep 26, 2025

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A more generalised solution here (that would also allow us to get rid of the separate is_equivalent_to call -- so might be quite a bit faster?) would be to add a third type relation, UnionSimplification (not sure what the best name would be really), which would sit in between TypeRelation::Subtyping and TypeRelation::Assignability. It would mostly behave the same way as subtyping (Any | int would not be considered simplifiable to Any), but Any <: Any, (Any | int) <: (int | Any) and (Any & str) <: Any would all be considered true under this type relation.

{
return;
} else if element_type.is_subtype_of(self.db, ty) {
} else if element_type.is_subtype_of(self.db, ty)
|| element_type
.into_intersection()
.is_some_and(|intersection| intersection.positive(self.db).contains(&ty))
{
to_remove.push(index);
} else if ty_negated.is_subtype_of(self.db, element_type) {
// We add `ty` to the union. We just checked that `~ty` is a subtype of an
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