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Fix #10867: Normalize after applyIfParameterized in superType #13253

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Sep 22, 2021
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Fix #10867: Normalize after applyIfParameterized in superType #13253

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6972e06
Fix #10867: Normalize after applyIfParameterized in superType
OlivierBlanvillain Aug 4, 2021
b9baa71
Reclassify recursive test case
OlivierBlanvillain Aug 4, 2021
a4fb041
Make normalizing superTypes valid nowhere
OlivierBlanvillain Sep 7, 2021
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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/core/Types.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -4110,7 +4110,7 @@ object Types {
cachedSuper = tycon match {
case tycon: HKTypeLambda => defn.AnyType
case tycon: TypeRef if tycon.symbol.isClass => tycon
case tycon: TypeProxy => tycon.superType.applyIfParameterized(args)
case tycon: TypeProxy => tycon.superType.applyIfParameterized(args).normalized
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I am not sure whether the caching is permissible here. If we normalize, are we certain that the next time around when we demand the super type of an applied type, we get the same normalization result? It does not look obvious to me.
Maybe we should do this instead.

    override def superType(using Context): Type =
      if ctx.period != validSuper then
        validSuper = if (tycon.isProvisional) Nowhere else ctx.period
        def reappliedSuper = tycon.superType.applyIfParameterized(args).normalized
        cachedSuper = tycon match
          case tycon: HKTypeLambda => defn.AnyType
          case tycon: TypeRef =>
            if tycon.symbol.isClass then tycon
            else
              if tycon.info.isInstanceof[MatchAlias] then validSuper = Nowhere
              reappliedSuper
          case tycon: TypeProxy => reappliedSuper
          case _ => defn.AnyType
      cachedSuper

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I updated the PR to change validity of the cache for normalizing match types.

case _ => defn.AnyType
}
validSuper = if (tycon.isProvisional) Nowhere else ctx.period
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2 changes: 1 addition & 1 deletion tests/pos-deep-subtype/9849.scala → ...ustom-args/allow-deep-subtypes/9849.scala
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@@ -1,4 +1,4 @@
type *:[A, B] = A match
type *:[A, B] = A match // error: Recursion limit exceeded.
case (B *: x) => A
case (x *: y) => x *: (B *: y)
case _ => A *: B
49 changes: 49 additions & 0 deletions tests/pos/10867.scala
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@@ -0,0 +1,49 @@
object Test {
type inserts[a, as <: Tuple] <: Tuple =
as match
case EmptyTuple => (a *: EmptyTuple) *: EmptyTuple
case y *: ys => (a *: y *: ys) *: Tuple.Map[inserts[a, ys], [t <: Tuple] =>> y *: t]

type inserts2[a] =
[as <: Tuple] =>> inserts[a, as]

type A = inserts [1, EmptyTuple]
type B = inserts2[1][EmptyTuple]

summon[A =:= ((1 *: EmptyTuple) *: EmptyTuple)]
summon[B =:= ((1 *: EmptyTuple) *: EmptyTuple)]
summon[A =:= B]

type H[t <: Tuple] = Tuple.Concat[t, EmptyTuple]

summon[H[A] =:= H[B]]

summon[Tuple.Concat[A, EmptyTuple] =:= Tuple.Concat[B, EmptyTuple]]
}

object Minimized {
type Concombre[X <: Tuple, +Y <: Tuple] <: Tuple = X match {
case EmptyTuple => Y
case x1 *: xs1 => X
}

type inserts[a, as <: Tuple] <: Tuple =
as match
case EmptyTuple => a *: EmptyTuple

type inserts2[a] =
[as <: Tuple] =>> inserts[a, as]

type A = inserts [1, EmptyTuple]
type B = inserts2[1][EmptyTuple]
type C = 1 *: EmptyTuple

summon[A =:= B]
summon[A =:= C]
summon[B =:= C]

type H[t <: Tuple] = Concombre[t, EmptyTuple]

summon[H[C] =:= H[A]]
summon[H[C] =:= H[B]]
}