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Fix #9088: Fix problematic code in productMirror #9089

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Fix #9088: Fix problematic code in productMirror #9089

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0accbb5
Fix #9088: Fix problematic code in productMirror
odersky May 31, 2020
9c16445
A better fix
odersky May 31, 2020
70e2c2b
Harden new productMirrorCode to work for erroneous code
odersky May 31, 2020
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7 changes: 6 additions & 1 deletion compiler/src/dotty/tools/dotc/typer/Synthesizer.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -277,9 +277,14 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
val elemLabels = accessors.map(acc => ConstantType(Constant(acc.name.toString)))
val (monoType, elemsType) = mirroredType match
case mirroredType: HKTypeLambda =>
def accessorType(acc: Symbol) =
if cls.typeParams.hasSameLengthAs(mirroredType.paramRefs) then
acc.info.subst(cls.typeParams, mirroredType.paramRefs)
else
acc.info
val elems =
mirroredType.derivedLambdaType(
resType = TypeOps.nestedPairs(accessors.map(mirroredType.memberInfo(_).widenExpr))
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mirroredType.memberInfo(_) makes no sense here. mirroredType is a type lambda, and as such not a legal prefix on which we can take a memberInfo. So I changed to just _.info which avoids the crash. However, I have no idea whether that's correct.

resType = TypeOps.nestedPairs(accessors.map(accessorType))
)
(mkMirroredMonoType(mirroredType), elems)
case _ =>
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6 changes: 3 additions & 3 deletions tests/run/poly-kinded-derives.scala
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Expand Up @@ -27,7 +27,7 @@ object Test extends App {
given t2 [T] as Functor[[U] =>> (T, U)] {}
given t3 [T, U] as Functor[[V] =>> (T, U, V)] {}

def derived[F[_]](using m: Mirror { type MirroredType = F ; type MirroredElemTypes[_] }, r: Functor[m.MirroredElemTypes]): Functor[F] = new Functor[F] {}
def derived[F[_]](using m: Mirror { type MirroredType[X] = F[X] ; type MirroredElemTypes[_] }, r: Functor[m.MirroredElemTypes]): Functor[F] = new Functor[F] {}
}

case class Mono(i: Int) derives Functor
Expand All @@ -43,7 +43,7 @@ object Test extends App {
given [C] as FunctorK[[F[_]] =>> C] {}
given [T] as FunctorK[[F[_]] =>> Tuple1[F[T]]]

def derived[F[_[_]]](using m: Mirror { type MirroredType = F ; type MirroredElemTypes[_[_]] }, r: FunctorK[m.MirroredElemTypes]): FunctorK[F] = new FunctorK[F] {}
def derived[F[_[_]]](using m: Mirror { type MirroredType[X[_]] = F[X] ; type MirroredElemTypes[_[_]] }, r: FunctorK[m.MirroredElemTypes]): FunctorK[F] = new FunctorK[F] {}
}

case class Mono(i: Int) derives FunctorK
Expand All @@ -61,7 +61,7 @@ object Test extends App {
given t2 as Bifunctor[[T, U] =>> (T, U)] {}
given t3 [T] as Bifunctor[[U, V] =>> (T, U, V)] {}

def derived[F[_, _]](using m: Mirror { type MirroredType = F ; type MirroredElemTypes[_, _] }, r: Bifunctor[m.MirroredElemTypes]): Bifunctor[F] = ???
def derived[F[_, _]](using m: Mirror { type MirroredType[X, Y] = F[X, Y] ; type MirroredElemTypes[_, _] }, r: Bifunctor[m.MirroredElemTypes]): Bifunctor[F] = ???
}

case class Mono(i: Int) derives Bifunctor
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