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Fix -Ytest-pickler with super trees #5516

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Merged
merged 1 commit into from
Oct 15, 2022
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Fix -Ytest-pickler with super trees #5516

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1 change: 1 addition & 0 deletions compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala
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Expand Up @@ -451,6 +451,7 @@ class TreePickler(pickler: TastyPickler) {
withLength {
pickleTree(qual);
if (!mix.isEmpty) {
// mixinType being a TypeRef when mix is non-empty is enforced by TreeChecker#checkSuper
val SuperType(_, mixinType: TypeRef) = tree.tpe: @unchecked
pickleTree(mix.withType(mixinType))
}
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17 changes: 17 additions & 0 deletions compiler/src/dotty/tools/dotc/transform/TreeChecker.scala
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Expand Up @@ -305,9 +305,26 @@ class TreeChecker extends Phase with SymTransformer {
override def excludeFromDoubleDeclCheck(sym: Symbol)(using Context): Boolean =
sym.isEffectivelyErased && sym.is(Private) && !sym.initial.is(Private)

/** Check that all invariants related to Super and SuperType are met */
def checkSuper(tree: Tree)(implicit ctx: Context): Unit = tree match
case Super(qual, mix) =>
tree.tpe match
case tp @ SuperType(thistpe, supertpe) =>
if (!mix.isEmpty)
assert(supertpe.isInstanceOf[TypeRef],
s"Precondition of pickling violated: the supertpe in $tp is not a TypeRef even though $tree has a non-empty mix")
case tp =>
assert(false, s"The type of a Super tree must be a SuperType, but $tree has type $tp")
case _ =>
tree.tpe match
case tp: SuperType =>
assert(false, s"The type of a non-Super tree must not be a SuperType, but $tree has type $tp")
case _ =>

override def typed(tree: untpd.Tree, pt: Type = WildcardType)(using Context): Tree = {
val tpdTree = super.typed(tree, pt)
Typer.assertPositioned(tree)
checkSuper(tpdTree)
if (ctx.erasedTypes)
// Can't be checked in earlier phases since `checkValue` is only run in
// Erasure (because running it in Typer would force too much)
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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala
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Expand Up @@ -255,7 +255,7 @@ trait TypeAssigner {
errorType("ambiguous parent class qualifier", pos)
}
val owntype =
if (mixinClass.exists) mixinClass.appliedRef
if (mixinClass.exists) mixinClass.typeRef
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I think neither old nor new version is right. What about this scenario?

trait A[X]
class B extends A[Int] {
  super[A] // should have type A[Int], not A, or A[X]
}

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Yes, it's a bit weird, but if we change this then we need to change the pickling/unpickling scheme for super which currently does:

            case SUPER =>
              val qual = readTerm()
              val (mixId, mixTpe) = ifBefore(end)(readQualId(), (untpd.EmptyTypeIdent, NoType))
tpd.Super(qual, mixId, ctx.mode.is(Mode.InSuperCall), mixTpe.typeSymbol

So won't work with mix being an AppliedType.

Alternatively we could change SuperType#underyling to work like SuperType#superType, currently they're different:

  abstract case class SuperType(thistpe: Type, supertpe: Type) extends CachedProxyType with SingletonType {
    override def underlying(implicit ctx: Context): Type = supertpe
    override def superType(implicit ctx: Context): Type =
thistpe.baseType(supertpe.typeSymbol)

But note that in practice I haven't found a case where the current definition breaks something, e.g. in findMember we call underlying on SuperType but that ends up working out since findMember keeps around the prefix of the call as pre which contains all the information we need to figure out the type parameters.

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I believe underlying in supertype is fine.

I don't see right now why pickler/unpickler has to change. Should we not instead change the TypeAssigner to do the same as SuperType$superType?

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@smarter smarter Mar 23, 2021 •
edited
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Coming back to this PR 2 years (!) later, I believe I'm still confused by why underlying and superType are different in SuperType, if I follow your advice of making TypeAssigner use the same logic as superType to set superTpe, then they would always be the same anyway. Would you mind taking another look at this?

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@odersky odersky Oct 15, 2022 •
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I don't have deep insights here either. underlying does not do baseType invocations, and superType should probably do that.

That said, I now think the change in TypeAssigner makes sense. If everything passes with that change, let's do it.

else if (!mix.isEmpty) findMixinSuper(cls.info)
else if (ctx.erasedTypes) cls.info.firstParent.typeConstructor
else {
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1 change: 0 additions & 1 deletion compiler/test/dotc/pos-test-pickling.blacklist
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Expand Up @@ -2,7 +2,6 @@ i94-nada.scala
i1812.scala
i1867.scala
i3067.scala
t247.scala
t2712-5.scala
t284-pos.scala
t3249
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