javabootclasspath supersedes jrt

[som-snytt]

To compile against a JDK 8 rt.jar, use -javabootclasspath rt.jar -nobootcp.

That disables the jrt class path for the ambient JDK, and puts the Scala libraries on the user class path.

(Alternatively, -usebootcp but list the libraries explicitly on -javabootclasspath.)

Fixes scala/bug#12257

[som-snytt]

Tested manually with -javabootclasspath ~/.sdkman/candidates/java/8.0.232-trava/jre/lib/rt.jar.

t12257b.scala:12: error: value getParams is not a member of java.security.interfaces.RSAPublicKey
    case rsa: RSAPublicKey => rsa.getParams
                                  ^

No automated test because it requires the old rt.jar which one is reluctant to put in the git repo.

It's reasonable to make jrt and -javabootclasspath mutually exclusive. (Note javac restricts --boot-class-path to JDK 8.)

https://docs.oracle.com/en/java/javase/19/docs/specs/man/javac.html#standard-options

[som-snytt]

@lrytz intentionally 2.13.11

[som-snytt]

Something about CI turns my quickie PR into a burner.

[som-snytt]

Corrected to use javaBootClassPath on JDK 8 as intended. On JDK 9+, use jrt unless user has specified -javabootclasspath.

Tested bootstrapped testAll under JDK 8.

Thanks Seth for cancelling the unhappy build.

[SethTisue]

on the one hand, this looks reasonable, and thanks @som-snytt for including the manual testing details

otoh this whole business isn't business I've been mixed up in before, so I'm not confident in my reviewing. maybe I can interest @retronym

[retronym]

I think this makes sense and seems unlikely to break existing builds.

[lrytz]

Current 2.13.x gives me

➜ sandbox ../build/quick/bin/scalac Test.scala
error: error while loading Object, Missing dependency 'object scala.native in compiler mirror', required by /modules/java.base/java/lang/Object.class
error: scala.reflect.internal.MissingRequirementError: object scala in compiler mirror not found.
	at scala.reflect.internal.MissingRequirementError$.signal(MissingRequirementError.scala:24)

Reverting this PR fixes it.

[lrytz]

#10350 also fixes it.

[som-snytt]

I meant to joke that indeed

seems unlikely to break existing builds.

You just can't run scalac.