Fix exhaustivity due to separate TypeVar lambdas #18616
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Remove the single use overload, replace with a much more used alternative Also return TypeVars instead of TypeTrees, so we don't have to unwrap the useless wrapper a bunch of times, and instead we wrap the few times we really do want to.
liufengyun
approved these changes
Oct 16, 2023
| @@ -779,7 +777,7 @@ object ProtoTypes { | |||
| pt => bounds :: Nil, | |||
| pt => represents.orElse(defn.AnyType)) | |||
| constrained(poly, untpd.EmptyTree, alwaysAddTypeVars = true, nestingLevel) | |||
| ._2.head.tpe.asInstanceOf[TypeVar] | |||
| ._2.head | |||
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From what I can see, the changes are only about APIs, which simplifies usage in several places, the logic is the same. /cc: @odersky
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By using newTypeVar, separate type lambdas are created. I think due to that, type parameter ordering doesn't
come into play. When the unapply usage is typed, the PolyType that is the method is added as a whole, with all
its type parameters, and its type vars are instantiated against that, allowing one type var to instantiate
against another parameter - so we must make the same thing happen in the SpaceEngine.
Due to that, when erasing, we need to erase pattern bound symbols underlying pattern bound symbols.
Then, rework ProtoType's constrained API. Firstly remove the single-use overload and replace it with a much
more used alternative. Secondly return TypeVars instead of TypeTrees, so we don't have to unwrap the useless
wrapper a bunch of times, and instead we wrap the few times we really do want to.
Refs #14224