Fix regression in instantiating type vars #16999
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dwijnand
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Previously, derivedSelect would incorrectly approximate `fn.R` by `? >: Nothing <: Any` in `i16997.min.scala`, which subsequently lead to a kind-incorrect type application `Any[Y]` that broke type inference. scala#16999 proposed to fix this by changing type inference, but it seems like we don't need to do that if we make sure our wildcards are always kind-correct. Note that the wildcard logic in lookupRefined could be removed: it seems like it was supposed to be used by `reduceProjection` according to its documentation, but the constructor of `NamedType` disallows wildcards as prefixes so it didn't actually do anything there.
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Previously, derivedSelect would incorrectly approximate `fn.R` by `? >: Nothing <: Any` in `i16997.min.scala`, which subsequently lead to a kind-incorrect type application `Any[Y]` that broke type inference. scala#16999 proposed to fix this by changing type inference, but it seems like we don't need to do that if we make sure our wildcards are always kind-correct. Note that the wildcard logic in lookupRefined could be removed: it seems like it was supposed to be used by `reduceProjection` according to its documentation, but the constructor of `NamedType` disallows wildcards as prefixes so it didn't actually do anything there. Co-Authored-By: Dale Wijnand <dale.wijnand@gmail.com>
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| @@ -4810,7 +4810,7 @@ object Types { | |||
| def hasLowerBound(using Context): Boolean = !currentEntry.loBound.isExactlyNothing | |||
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| /** For uninstantiated type variables: Is the upper bound different from Any? */ | |||
| def hasUpperBound(using Context): Boolean = !currentEntry.hiBound.finalResultType.isExactlyAny | |||
| def hasUpperBound(using Context): Boolean = !currentEntry.hiBound.finalResultType.isRef(defn.AnyClass) // so also `Any[..]` | |||
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This is weird: Any is not kind-polymorphic, it's not supposed to be applicable to arguments. I've opened a PR which I believe fixes the root issue: #17025
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Fixes #16997