Compiler crashes with "trying to do lub/glb of typevar" #10722
Description
When trying to compile the following type class with Scala 2.12.4:
/**
* Type class witnessing that the result of stripping type constructor `F` (or a subtype of `F`) off `L` is `Out`.
*/
trait StripTC[L, F[_]] {
type Out
}
object StripTC {
type Aux[L, F[_], Out0] = StripTC[L, F] { type Out = Out0 }
implicit def stripTCInstance[H, F[_], FH <: F[H]]: Aux[FH, F, H] =
new StripTC[FH, F] { type Out = H }
}
object Test {
implicitly[StripTC[List[Int], List]]
}The compiler crashes with the following message:
scala.reflect.internal.FatalError:
[error] trying to do lub/glb of typevar ?FH
[error] while compiling: /Users/rui/Downloads/test/StripTC.scala
[error] during phase: typer
[error] library version: version 2.12.4
[error] compiler version: version 2.12.4
[error] reconstructed args: -classpath /Users/rui/Downloads/test/target/scala-2.12/classes -bootclasspath /Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/sunrsasign.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/classes:/Users/rui/.sbt/boot/scala-2.12.4/lib/scala-library.jar
[error]
[error] last tree to typer: Ident(StripTC)
[error] tree position: line 42 of /Users/rui/Downloads/test/StripTC.scala
[error] tree tpe: StripTC.type
[error] symbol: object StripTC
[error] symbol definition: object StripTC (a ModuleSymbol)
[error] symbol package: <empty>
[error] symbol owners: object StripTC
[error] call site: object Test in package <empty>
[error]
[error] == Source file context for tree position ==
[error]
[error] 39 }
[error] 40
[error] 41 object Test {
[error] 42 implicitly[StripTC[List[Int], List]]
[error] 43 }
This may be related or a duplicate of #10519, #10514, #8602 or #5559. I don't have the required knowledge about the Scala compiler to know if this is a duplicate, so if that's the case please close this and point me to the right issue :)