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Admit parametric aliases of classes in parent typing #18849

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15 changes: 10 additions & 5 deletions compiler/src/dotty/tools/dotc/core/TypeApplications.scala
Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,7 @@ object TypeApplications {

def apply(tycon: Type)(using Context): Type =
assert(tycon.typeParams.nonEmpty, tycon)
tycon.EtaExpand(tycon.typeParamSymbols)
tycon.etaExpand(tycon.typeParamSymbols)

/** Test that the parameter bounds in a hk type lambda `[X1,...,Xn] => C[X1, ..., Xn]`
* contain the bounds of the type parameters of `C`. This is necessary to be able to
Expand Down Expand Up @@ -71,7 +71,7 @@ object TypeApplications {
*/
def EtaExpandIfHK(tparams: List[TypeParamInfo], args: List[Type])(using Context): List[Type] =
if (tparams.isEmpty) args
else args.zipWithConserve(tparams)((arg, tparam) => arg.EtaExpandIfHK(tparam.paramInfoOrCompleter))
else args.zipWithConserve(tparams)((arg, tparam) => arg.etaExpandIfHK(tparam.paramInfoOrCompleter))

/** A type map that tries to reduce (part of) the result type of the type lambda `tycon`
* with the given `args`(some of which are wildcard arguments represented by type bounds).
Expand Down Expand Up @@ -245,7 +245,7 @@ class TypeApplications(val self: Type) extends AnyVal {
def topType(using Context): Type =
if self.hasSimpleKind then
defn.AnyType
else EtaExpand(self.typeParams) match
else etaExpand(self.typeParams) match
case tp: HKTypeLambda =>
tp.derivedLambdaType(resType = tp.resultType.topType)
case _ =>
Expand Down Expand Up @@ -302,7 +302,7 @@ class TypeApplications(val self: Type) extends AnyVal {
/** Convert a type constructor `TC` which has type parameters `X1, ..., Xn`
* to `[X1, ..., Xn] -> TC[X1, ..., Xn]`.
*/
def EtaExpand(tparams: List[TypeParamInfo])(using Context): Type =
def etaExpand(tparams: List[TypeParamInfo])(using Context): Type =
HKTypeLambda.fromParams(tparams, self.appliedTo(tparams.map(_.paramRef)))
//.ensuring(res => res.EtaReduce =:= self, s"res = $res, core = ${res.EtaReduce}, self = $self, hc = ${res.hashCode}")

Expand All @@ -311,7 +311,7 @@ class TypeApplications(val self: Type) extends AnyVal {
if (isLambdaSub) self else EtaExpansion(self)

/** Eta expand if `self` is a (non-lambda) class reference and `bound` is a higher-kinded type */
def EtaExpandIfHK(bound: Type)(using Context): Type = {
def etaExpandIfHK(bound: Type)(using Context): Type = {
val hkParams = bound.hkTypeParams
if (hkParams.isEmpty) self
else self match {
Expand All @@ -321,6 +321,11 @@ class TypeApplications(val self: Type) extends AnyVal {
}
}

/** Maps [Ts] => C[Ts] to C */
def etaCollapse(using Context): Type = self match
case EtaExpansion(classType) => classType
case _ => self

/** The type representing
*
* T[U1, ..., Un]
Expand Down
2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/core/TypeComparer.scala
Original file line number Diff line number Diff line change
Expand Up @@ -746,7 +746,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
case _ =>
val tparams1 = tp1.typeParams
if (tparams1.nonEmpty)
return recur(tp1.EtaExpand(tparams1), tp2) || fourthTry
return recur(tp1.etaExpand(tparams1), tp2) || fourthTry
tp2 match {
case EtaExpansion(tycon2: TypeRef) if tycon2.symbol.isClass && tycon2.symbol.is(JavaDefined) =>
recur(tp1, tycon2) || fourthTry
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -832,7 +832,7 @@ class Scala2Unpickler(bytes: Array[Byte], classRoot: ClassDenotation, moduleClas
}
else if args.nonEmpty then
tycon.safeAppliedTo(EtaExpandIfHK(sym.typeParams, args.map(translateTempPoly)))
else if (sym.typeParams.nonEmpty) tycon.EtaExpand(sym.typeParams)
else if (sym.typeParams.nonEmpty) tycon.etaExpand(sym.typeParams)
else tycon
case TYPEBOUNDStpe =>
val lo = readTypeRef()
Expand Down
2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/typer/Deriving.scala
Original file line number Diff line number Diff line change
Expand Up @@ -165,7 +165,7 @@ trait Deriving {
// case (a) ... see description above
val derivedParams = clsParams.dropRight(instanceArity)
val instanceType =
if (instanceArity == clsArity) clsType.EtaExpand(clsParams)
if (instanceArity == clsArity) clsType.etaExpand(clsParams)
else {
val derivedParamTypes = derivedParams.map(_.typeRef)

Expand Down
4 changes: 2 additions & 2 deletions compiler/src/dotty/tools/dotc/typer/Namer.scala
Original file line number Diff line number Diff line change
Expand Up @@ -1197,7 +1197,7 @@ class Namer { typer: Typer =>
val forwarderName = checkNoConflict(alias.toTypeName, isPrivate = false, span)
var target = pathType.select(sym)
if target.typeParams.nonEmpty then
target = target.EtaExpand(target.typeParams)
target = target.etaExpand(target.typeParams)
newSymbol(
cls, forwarderName,
Exported | Final,
Expand Down Expand Up @@ -1518,7 +1518,7 @@ class Namer { typer: Typer =>

def typedParentType(tree: untpd.Tree): tpd.Tree =
val parentTpt = typer.typedType(parent, AnyTypeConstructorProto)
val ptpe = parentTpt.tpe
val ptpe = parentTpt.tpe.dealias.etaCollapse
if ptpe.typeParams.nonEmpty
&& ptpe.underlyingClassRef(refinementOK = false).exists
then
Expand Down
2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/typer/RefChecks.scala
Original file line number Diff line number Diff line change
Expand Up @@ -372,7 +372,7 @@ object RefChecks {
*/
def checkOverride(checkSubType: (Type, Type) => Context ?=> Boolean, member: Symbol, other: Symbol): Unit =
def memberTp(self: Type) =
if (member.isClass) TypeAlias(member.typeRef.EtaExpand(member.typeParams))
if (member.isClass) TypeAlias(member.typeRef.etaExpand(member.typeParams))
else self.memberInfo(member)
def otherTp(self: Type) =
self.memberInfo(other)
Expand Down
2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/typer/Typer.scala
Original file line number Diff line number Diff line change
Expand Up @@ -4306,7 +4306,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
AppliedType(tree.tpe, tp.typeParams.map(Function.const(TypeBounds.empty)))
else
// Eta-expand higher-kinded type
tree.tpe.EtaExpand(tp.typeParamSymbols)
tree.tpe.etaExpand(tp.typeParamSymbols)
tree.withType(tp1)
}
if (ctx.mode.is(Mode.Pattern) || ctx.mode.isQuotedPattern || tree1.tpe <:< pt) tree1
Expand Down
4 changes: 2 additions & 2 deletions tests/neg/i4557.scala
Original file line number Diff line number Diff line change
Expand Up @@ -9,11 +9,11 @@ object O {
type S0[X, Y] = C1[X, Y]
type S1 = C1[Int] // error

class D0 extends T0 // error
class D0 extends T0 // was error, now ok
class D1 extends T0[Int]
class D2 extends T0[String, Int] // error

class E0 extends S0 // error
class E0 extends S0 // was error, now ok
class E1 extends S0[Int] // error
class E2 extends S0[String, Int]
}
15 changes: 15 additions & 0 deletions tests/pos/i18623.scala
Original file line number Diff line number Diff line change
@@ -0,0 +1,15 @@
final abstract class ForcedRecompilationToken[T]
object ForcedRecompilationToken {
implicit def default: ForcedRecompilationToken["abc"] = null
}

class GoodNoParens[T](implicit ev: ForcedRecompilationToken[T])
type BadNoParens[T] = GoodNoParens[T]

// error
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This is no longer an error, so we should delete this comment.

object A extends BadNoParens

// ok
object B extends BadNoParens()
object C extends GoodNoParens

20 changes: 20 additions & 0 deletions tests/pos/i18623a.scala
Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
final abstract class ForcedRecompilationToken[T]
object ForcedRecompilationToken {
implicit def default: ForcedRecompilationToken["abc"] = null
}

object x {
class GoodNoParens[T](implicit ev: ForcedRecompilationToken[T])
}
export x.GoodNoParens as BadNoParens

// error
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Same here

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We usually leave the // error markers in the pos files. Less work to do, and it's useful to see what got fixed.

object A extends BadNoParens

// ok
object B extends BadNoParens()
object C extends x.GoodNoParens

object App extends App {
println("compiled")
}