Defend against AliasingBounds #23668
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Ready for review in the sense of open to suggestions. |
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I appreciate the Odersky PR that says "we need a better solution". This is such a PR, if only it had a PR label. |
odersky
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Aug 6, 2025
| val target = | ||
| val target0 = explicitInfo.firstParamTypes.head // required for extension method, the putative receiver | ||
| target0.dealiasKeepOpaques.typeSymbol.info | ||
| target0.dealiasKeepOpaques.typeSymbol.info match |
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This is kind of weird since dealias does skip aliasing bounds. It would be good to get an explanation what exactly goes wrong here. What's the type of target0.dealiasKeepOpaques in the failing test? What is its info? Is there an opaque type involved?
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The correct working idiom is
explicitInfo.firstParamTypes.head.typeSymbol.typeRef.dealiasKeepOpaques
but requires reworking https://github.com/scala/scala3/pull/22502/files
or dealias should handle TypeAlias directly.
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In refchecks for extension methods, obtain a TypeRef of the receiver parameter type, so that it is correctly dealiased. The prior idiom produced a TypeAlias.
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Flaky test in CB probes |
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Fixes #23666
Improve use of existing API. The fix is instead of using param's
symbol.info, usesymbol.typeRef.dealiasand follow upper bounds, with a special case in the "subsumes" check for type param; and also a guard to not dealias an opaque type by using its bounds.