Re: Toolbox typecheck throws MatchError for higher-kinded path-dependent type

On Wed, Jul 29, 2015 at 6:54 AM Daniel Armak <[email protected]> wrote:

> Hi,
>
> I encountered this error trying to compile code that uses the shapeless
> ~?> typeclass with the toolbox, and simplified it to this:
>
>
> import scala.reflect.runtime.currentMirror
> import scala.tools.reflect.ToolBox
>
> val tb = ToolBox(currentMirror).mkToolBox()
> val source = """{
>   import scala.language.higherKinds
>
>   class Outer[X] {
>     class Inner[Y]
>   }
>   class Other[T[_]]
>
>   new Other[Outer[Int]#Inner]()
> }"""
>
> val tree = tb.parse(source)
> tb.typecheck(tree).tpe
>
> This fails with:
>
> Exception in thread "main" scala.MatchError: <tree with deferred refcheck> (of class scala.tools.nsc.ast.Trees$TypeTreeWithDeferredRefCheck)
>     at scala.reflect.internal.Importers$StandardImporter.recreateTree(Importers.scala:309)
>
> (Full stack trace here
> <https://gist.github.com/danarmak/c917b4f35e5d4d6ccbc7>)
>
> I’m using scala 2.11.7.
>
Thanks for the report.

The bug is in Importers, which copies a tree from one compiler universe
into another.

I notice that @mandubian also ran into the same problem
<https://gist.github.com/mandubian/807961eb9a8911f45894>.

It fails to account for a special tree, TypeTreeWithDeferredWithRefCheck
that exists between the typer and refchecks compiler phases, and is used
when typechecking higher kinded type applications.

I’ve lodged your report as SI-9421
<https://issues.scala-lang.org/browse/SI-9421>.

Fixing it would require adding a default case in
src/reflect/scala/reflect/internal/Importers.scala importTree that
forwarded to an extension hook that could be implemented in nsc.Global.
This pattern is already used in TreePrinters, see in particular xprinttree
<https://github.com/scala/scala/blob/v2.11.6/src/compiler/scala/tools/nsc/ast/Printers.scala#L46-46>
​
-jason

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