Pattern matching over emptyValDef and pendingSuperCall trees

[Den Sh]

Hello,

I've stumbled upon an unexpected problem with reflection pattern matching:

scala> val u = scala.reflect.runtime.universe
u: scala.reflect.api.JavaUniverse = scala.reflect.runtime.JavaUniverse@18b679e1

scala> u.emptyValDef match { case u.emptyValDef => }
<console>:20: error: stable identifier required, but u.emptyValDef found.
 Note that value emptyValDef is not stable because its type, => u.ValDef, is volatile.
              u.emptyValDef match { case u.emptyValDef => }
                                           ^

scala> u.pendingSuperCall match { case u.pendingSuperCall => }
<console>:20: error: stable identifier required, but u.pendingSuperCall found.
 Note that value pendingSuperCall is not stable because its type, => u.Apply, is volatile.
              u.pendingSuperCall match { case u.pendingSuperCall => }
                                                ^

Can anything be done to aid pattern matching over this values ?

[Adriaan Moors]

ah yes, I wonder if patterns need to exclude identifiers that would be stable if it wasn't for their volatile type

It's unsound to select types on a prefix with a volatile type, but it should be fine to compare it for equality.

I logged https://issues.scala-lang.org/browse/SI-6815

in the short term, an extractor could help I suppose