Support variance annotations in -Ykind-projector mode
#12341
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smarter
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May 5, 2021
| private def makeKindProjectorTypeDef(name: TypeName): TypeDef = | ||
| TypeDef(name, WildcardTypeBoundsTree()).withFlags(Param) | ||
| private def makeKindProjectorTypeDef(name: TypeName): TypeDef = { | ||
| val isVarianceAnnotated = name.lastPart.startsWith("+") || name.lastPart.startsWith("-") |
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Couldn't name.startsWith be used given that these are user-written names and so should only have one part?
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@smarter Changed to name.startsWith
| TypeDef(name, WildcardTypeBoundsTree()).withFlags(Param) | ||
| private def makeKindProjectorTypeDef(name: TypeName): TypeDef = { | ||
| val isVarianceAnnotated = name.lastPart.startsWith("+") || name.lastPart.startsWith("-") | ||
| val unannotatedName = if (isVarianceAnnotated) name.mapLast(_.drop(1)) else name |
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Would be nice to add a comment mentioning that we can strip the variance because it's inferred.
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@smarter Added a comment explaining the decision to just strip the variance
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This change expands the supported subset of `kind-projector` syntax, specifically: * `+*` and `-*` variance annotated variants of `*` placeholder * Variance annotated named parameters in `λ` - `λ[(`-R`, `+E`, `+A`) => F[R, E, A]]`
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This change expands the supported subset of
kind-projectorsyntax, specifically:+*and-*variance annotated versions of the*placeholderλsyntax -λ[(`-R`, `+E`, `+A`) => F[R, E, A]]This change ignores the variance flag specified using
kind-projector's syntax – since variance annotations in type lambdas are deprecated in Scala 3, the real variance of a variable will be inferred separately. I believe that may be acceptable since-Ykind-projector's raison d'être is to allow cross-compilation with existing Scala 2 code, not for writing new code, that is the variance annotations may be assumed to have been checked by the Scala 2 compiler.Related PRs and issues: #7139 #7775
Prompted by discussion in scala/scala#9605