Fix isEffectivelySingleton #20486
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Fix isEffectivelySingleton #20486
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As usual, OrTypes need to be excluded. a.type | b.type is not effectively a singleton. It seems to be an easy trap to fall into. Follow-up to scala#20474
noti0na1
reviewed
May 28, 2024
| val b1: a.type = a | ||
| val b2: a.type & B = a.asInstanceOf[a.type & B] | ||
| val b3: c.type & A = c | ||
| val b4: a.type | c.type = c |
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Can you add the test below for OrType as well?
val b5: a.type | a.type = a
val d5: b5.type = a // okThere was a problem hiding this comment.
I don't think that will work. Have you tried it? I see no strong reason to make it work.
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It works in 3.4.2: https://scastie.scala-lang.org/A6PehvQvRhW2sUPVVtHiuA
I think the atoms is doing all these checks.
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Ah, yes, atoms would do it. Bit it's an extreme corner case. Not sure we want to make sure it works in the general case. Because in this case we'd also have to accept
val b6: (a.type & A) | a.type
val d6: b6.type = a // okand I am not sure atoms would help us here.
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I propose we merge without further refinements, since it plugs a recent soundness hole. |
noti0na1
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May 28, 2024
WojciechMazur
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Jul 9, 2024
Backports #20486 to the LTS branch. PR submitted by the release tooling. [skip ci]
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As usual, OrTypes need to be excluded. a.type | b.type is not effectively a singleton. It seems to be an easy trap to fall into.
Follow-up to #20474