Better comparisons for type projections #17092
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We already implemented in essence the rule suggested in lampepfl/dotty-feature-requests#14: ``` Γ ⊨ p : T ------------------------ (Sel-<:-Proj) Γ ⊨ p.A <: T#A ``` This rule is implemented in `isSubPrefix`. But we did not get to check that since we concluded prematurely that an alias type would never match. The alias type in question in i17064.scala was ```scala Outer#Inner ``` Since `Outer` is not a path, the asSeenFrom to recover the info of `Outer#Inner this got approximated with a `Nothing` argument and therefore the alias failed. It is important in this case that we could still succeed with a `isSubPrefix` test, which comes later. So we should not return `false` when the prefix is not a singleton. Fixes scala#17064
smarter
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Mar 13, 2023
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| def hasPrecisePrefix(tp: NamedType) = | ||
| tp.prefix.isSingleton || tp.prefix == NoPrefix |
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This seems fine, but since asSeenFrom itself uses TypeOps.isLegalPrefix for this purpose, wouldn't it make sense to also use it here to ensure the checks stay aligned?
`NoPrefix.isStable` already returns true.
smarter
reviewed
Mar 25, 2023
| * See pos/i17064.scala for a test case | ||
| */ | ||
| def hasStablePrefix(tp: NamedType) = | ||
| tp.prefix.isStable |
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I dropped the NoPrefix check since it's already implied by isStable
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Ah yes, I overlooked that.
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We already implemented in essence the rule suggested in lampepfl/dotty-feature-requests#14:
This rule is implemented in
isSubPrefix. But we did not get to check that since we concluded prematurely that an alias type would never match. The alias type in question in i17064.scala wasSince
Outeris not a path, the asSeenFrom to recover the info ofOuter#Innergot approximated with aNothingargument and therefore the alias failed. It is important in this case that we could still succeed with aisSubPrefixtest, which comes later. So we should not returnfalsewhen the prefix is not a singleton.Fixes #17064