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Normalize reference to undet param in stabilizer #10760

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merged 1 commit into from May 8, 2024
Merged

Normalize reference to undet param in stabilizer #10760

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7 changes: 6 additions & 1 deletion src/compiler/scala/tools/nsc/typechecker/Typers.scala
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Expand Up @@ -5524,7 +5524,12 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
context.pendingStabilizers ::= vdef
qual.changeOwner(context.owner -> vsym)
val newQual = Ident(vsym) setType singleType(NoPrefix, vsym) setPos qual.pos.focus
return typedSelect(tree, newQual, name)
return typedSelect(tree, newQual, name).modifyType(_.map {
// very specific fix for scala/bug#12987 (details in the ticket)
case t: AliasTypeRef if t.pre.termSymbol == vsym && context.undetparams.contains(t.normalize.typeSymbol) =>
t.normalize
case t => t
})
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In short, given a method def m(b: FT, o: Option[I]): Int and a stabilizer is inserted at some call site stabilizer$1.m(b, None)

If FT is a type parameter, stabilizer$1.m has a MethodType where the parameter type FT is subsituted by asSeenFrom.

If FT is a type member, the parameter type ends up being AliasNoArgsTypeRef(stabilizer$1.type, FT), which is equivalent in theory, but instantiateTypeParams doesn't see through this alias.

More details in scala/bug#12987.

}

val tree1 = tree match {
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30 changes: 30 additions & 0 deletions test/files/pos/t12987.scala
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@@ -0,0 +1,30 @@
object typeMember {
class Foo {
type FT
class I
def m(b: FT, o: Option[I]): Int = 0
}

object Test {
def f[T]: Foo { type FT = T } = ???
def t = {
val b: Any = ???
f.m(b, None)
}
}
}

object typeParam {
class Foo[FT] {
class I
def m(b: FT, o: Option[I]): Int = 0
}

object Test {
def f[T]: Foo[T] = ???
def t = {
val b: Any = ???
f.m(b, None)
}
}
}