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Fix #3976: Fix Eq method for enums with higher-kinded parameters #3982

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merged 2 commits into from
Feb 12, 2018
Merged

Fix #3976: Fix Eq method for enums with higher-kinded parameters #3982

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84e62c3
Fix #3976: Fix Eq method for enums with higher-kinded parameters
odersky Feb 11, 2018
706304f
More extensive tests and relaed fixes
odersky Feb 12, 2018
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25 changes: 21 additions & 4 deletions compiler/src/dotty/tools/dotc/ast/Desugar.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -341,8 +341,21 @@ object desugar {
(if (args.isEmpty) tycon else AppliedTypeTree(tycon, args))
.withPos(cdef.pos.startPos)

def appliedRef(tycon: Tree, tparams: List[TypeDef] = constrTparams) =
appliedTypeTree(tycon, tparams map refOfDef)
def appliedRef(tycon: Tree, tparams: List[TypeDef] = constrTparams, widenHK: Boolean = false) = {
var targs = for (tparam <- tparams) yield {
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var -> val

val targ = refOfDef(tparam)
def fullyApplied(tparam: Tree): Tree = tparam match {
case TypeDef(_, LambdaTypeTree(tparams, body)) =>
AppliedTypeTree(targ, tparams.map(_ => TypeBoundsTree(EmptyTree, EmptyTree)))
case TypeDef(_, rhs: DerivedTypeTree) =>
fullyApplied(rhs.watched)
case _ =>
targ
}
if (widenHK) fullyApplied(tparam) else targ
}
appliedTypeTree(tycon, targs)
}

// a reference to the class type bound by `cdef`, with type parameters coming from the constructor
val classTypeRef = appliedRef(classTycon)
Expand Down Expand Up @@ -431,12 +444,16 @@ object desugar {
//
// implicit def eqInstance[T1$1, ..., Tn$1, T1$2, ..., Tn$2](implicit
// ev1: Eq[T1$1, T1$2], ..., evn: Eq[Tn$1, Tn$2]])
// : Eq[C[T1$1, ..., Tn$1], C[T1$2, ..., Tn$2]] = Eq
// : Eq[C[T1$, ..., Tn$1], C[T1$2, ..., Tn$2]] = Eq
//
// If any of the T_i are higher-kinded, say `Ti[X1 >: L1 <: U1, ..., Xm >: Lm <: Um]`,
// the corresponding type parameters for $ev_i are `Ti$1[_, ..., _], Ti$2[_, ..., _]`
// (with m underscores `_`).
def eqInstance = {
val leftParams = constrTparams.map(derivedTypeParam(_, "$1"))
val rightParams = constrTparams.map(derivedTypeParam(_, "$2"))
val subInstances = (leftParams, rightParams).zipped.map((param1, param2) =>
appliedRef(ref(defn.EqType), List(param1, param2)))
appliedRef(ref(defn.EqType), List(param1, param2), widenHK = true))
DefDef(
name = nme.eqInstance,
tparams = leftParams ++ rightParams,
Expand Down
1 change: 1 addition & 0 deletions tests/pos/i3976.scala
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@@ -0,0 +1 @@
enum class Hoge[F[_]]
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I would add a test with an M[_[_]] param, and perhaps some code that exercises the generated Eq implicits too to make sure it works as expected.