Crash with inherited apply from separately compiled class

[adriaanm]

Regression introduced in 2.11.9 by scala/scala#5730, sadly not fixed in 2.11.10. (2.12.2 PR: scala/scala#5816)

First compile:

trait Companion { def apply(value: String): Any = ??? }

Then, with the previously compiled trait on the classpath, compile:

object o extends Companion
case class o(value: String)

Crash:

error:
  Unknown type: <error>, <error> 
[class scala.reflect.internal.Types$ErrorType$, class scala.reflect.internal.Types$ErrorType$]
 TypeRef? false
     while compiling: o.scala
        during phase: icode

[adriaanm]

The full-blown companion is from akka-http: akka/akka-http@2dd5d4b#diff-423d3ac8d183bdbcde68bfb462daf7ebR70

It looks like the concrete apply/unapply methods in ModeledCustomHeaderCompanion are intended to be called, but they were being overridden by the synthetic ones generated for case classes by the compiler (once this bug is fixed, the inherited methods will be used instead of the synthetic ones). /cc @jrudolph