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Fix #3630: Handle classtag searches with wildcard arguments #3718

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Merged
merged 1 commit into from
Jan 13, 2018
Merged

Fix #3630: Handle classtag searches with wildcard arguments #3718

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1 change: 1 addition & 0 deletions compiler/src/dotty/tools/dotc/core/TypeErasure.scala
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Expand Up @@ -320,6 +320,7 @@ object TypeErasure {
case _ => false
}
case tp: TypeParamRef => false
case tp: TypeBounds => false
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Would hasStableErasure(tp.lo) && hasStableErasure(tp.hi) be incorrect?

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No, because we fall into this case also via TypeProxy.

case tp: TypeProxy => hasStableErasure(tp.superType)
case tp: AndOrType => hasStableErasure(tp.tp1) && hasStableErasure(tp.tp2)
case _ => false
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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/typer/Implicits.scala
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Expand Up @@ -564,7 +564,7 @@ trait Implicits { self: Typer =>
* synthesize a class tag for `T`.
*/
def synthesizedClassTag(formal: Type)(implicit ctx: Context): Tree =
formal.argTypes match {
formal.argInfos match {
case arg :: Nil =>
fullyDefinedType(arg, "ClassTag argument", pos) match {
case defn.ArrayOf(elemTp) =>
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1 change: 1 addition & 0 deletions tests/neg/i3630.scala
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@@ -0,0 +1 @@
class U { Array(Array(2), Array("a")) } // error: no classtag
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Do we really need to disallow this? It seems to work OK in scalac.

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The full error message says:

No ClassTag available for Array[_ >: Int & String <: Int | String]

The inferred type of the outer array is

Array[Array[_ >: Int & String <: Int | String]]

That is indeed the best type. But there's no ClassTag. We could infer some wider type such as

Array[AnyRef](Array(2), Array("a"))

for the outer array. But it would be a special case. And I am not sure whether in the end it would not be better to reject this weird construction as an error and demand that the user write

Array[AnyRef](Array(2), Array("a"))

explicitly.