Package object extends deprecated under -Xsource:3 not dotty #12886
Description
Reproduction steps
Scala version: 2.13.12
package object p extends Runnable {
def run() = ()
}then
$ scalac -Xsource:3 -d /tmp/sandbox po.scala
po.scala:2: error: package object inheritance is deprecated (https://github.com/scala/scala-dev/issues/441);
drop the `extends` clause or use a regular object instead
Scala 3 migration messages are errors under -Xsource:3. Use -Wconf / @nowarn to filter them or add -Xmigration to demote them to warnings.
Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=scala3-migration
package object p extends Runnable {
^
1 error
Problem
Dotty doesn't give a peep in 3.3.