Fix #18246: correctly compute capture sets in TypeComparer.glb
#18254
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Linyxus
changed the title
TypeComparer.glb
Linyxus
changed the title
TypeComparer.glbTypeComparer.glb
I guess that should be \squarecap not \squarecup. |
odersky
approved these changes
Jul 23, 2023
| && tp1.isBoxedCapturing == tp2.isBoxedCapturing | ||
| then | ||
| parent1 & tp2 | ||
| if refs2.isAlwaysEmpty then parent1 & tp2 |
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Maybe we should roll the isAlwaysEmpty optimization into capturing?
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Intuitively,
glb(S1^C1, S2^C2)should captureC1 ⊓ C2, where⊓denotes the glb of capture sets. When computingglb(tp1, tp2), iftp1matchesCapturingType(parent1, refs1), it capturesC0 ++ refs1whereC0is the nested capture sets insideparent1. Denote the capture set oftp2withC2, the result should capture(C0 ++ refs1) ⊓ C2. Presumably,⊓distributes over the union (++); therefore(C0 ++ refs1) ⊓ C2equalsC0 ⊓ C2 ++ refs1 ⊓ C2.Previously, if
C2is a subcapture ofrefs1, it is simply dropped. However, based on the above reasoning, we haverefs1 ⊓ C2equalsC2; thereforeC0 ⊓ C2 ++ refs1 ⊓ C2equalsC0 ⊓ C2 ++ C2.C2should not be dropped, but rather kept. This PR fixes the logic to behave correctly.Fixes #18246.