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[red-knot] Simplify unions of T and ~T (#15400)

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## Summary

Simplify unions of `T` and `~T` to `object`.

## Test Plan

Adapted existing tests.
This commit is contained in:
David Peter 2025-01-10 23:00:52 +01:00 • committed by GitHub
parent 398f2e8b0c
commit 2d82445794
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3 changed files with 29 additions and 15 deletions
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13
crates/red_knot_python_semantic/src/types/builder.rs
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@ -65,6 +65,8 @@ impl<'db> UnionBuilder<'db> {
let mut to_add = ty;
let mut to_remove = SmallVec::<[usize; 2]>::new();
let ty_negated = ty.negate(self.db);
for (index, element) in self.elements.iter().enumerate() {
if Some(*element) == bool_pair {
to_add = KnownClass::Bool.to_instance(self.db);
@ -80,6 +82,17 @@ impl<'db> UnionBuilder<'db> {
return self;
} else if element.is_subtype_of(self.db, ty) {
to_remove.push(index);
} else if ty_negated.is_subtype_of(self.db, *element) {
// We add `ty` to the union. We just checked that `~ty` is a subtype of an existing `element`.
// This also means that `~ty | ty` is a subtype of `element | ty`, because both elements in the
// first union are subtypes of the corresponding elements in the second union. But `~ty | ty` is
// just `object`. Since `object` is a subtype of `element | ty`, we can only conclude that
// `element | ty` must be `object` (object has no other supertypes). This means we can simplify
// the whole union to just `object`, since all other potential elements would also be subtypes of
// `object`.
self.elements.clear();
self.elements.push(KnownClass::Object.to_instance(self.db));
return self;
}
}
match to_remove[..] {