3.0.0-RC2 + 2.13.5 = TASTy signature has wrong version

[aeons]

reproduction steps

Using scala 2.13.5 and 3.0.0-RC2

$ cat A.scala
package foo
class A

$ cat B.scala
package bar
class B extends foo.A

$ scala3-compiler A.scala
$ scalac -Ytasty-reader B.scala
error: error while loading A, class file './foo/A.class' is broken
(class scala.tools.tasty.UnpickleException/TASTy signature has wrong version.
 expected: {majorVersion: 28, minorVersion: 0 [unstable release: 1]}
 found   : {majorVersion: 28, minorVersion: 0 [unstable release: 3]}

This TASTy file was produced by an unstable release.
To read this TASTy file, your tooling must be at the same version.
The TASTy file was produced by Scala 3.0.0-RC2.
Note that your tooling is currently using an unstable TASTy version.)
B.scala:2: error: illegal inheritance;
 self-type bar.B does not conform to foo.A's selftype foo.A
class B extends foo.A
                    ^
2 errors

problem

Seems like 3.0.0-RC2 has bumped the tasty signature version, to something that is not compatible with the tasty reader in 2.13.5.

[lrytz]

We are happy to do a 2.13.6 release soon for Scala 3 interop. @bishabosha will let us know when is a good moment for that - there are some open issues. Also, if the 2.13.6 happens before Scala 3 final is out, it would be good to avoid the same breakage for the Scala 3 final.

[SethTisue]

this is also under discussion at https://contributors.scala-lang.org/t/scala-2-13-6-planning/4975/2

[bishabosha]

this should be fixed by scala/scala#9617