implement scalac script in Scala

[bishabosha]

fixes #15173
fixes #15221

[bishabosha]

@michelou also tagging you here for when this is merged

[bishabosha]

tested in project/scripts/winCmdTests and project/scripts/bootstrappedOnlyCmdTests

[sjrd]

Same confusion here. This did not use to be special in the old script. Why is it special now?

[bishabosha]

This is copied from the Scala script, I think there was the same Cygwin bug there

[philwalk]

I don't think it's related to cygwin; the code and comments appear to be inherited from the scala2 version of the script.

[sjrd]

Are these things that the cs runner would be able to pass to MainGenericRunner?

[bishabosha]

CS can configure properties, but probably does not have a magic variable for the launch directory (-Dscala.home was copied from the Scala script for use in programs), I don't think it should be supported in CS because the directory structure is not equivalent

[philwalk]

Some scripts will fail if -Dscala.home=$PROG_HOME isn't defined.
And there is no simple alternative to figuring out the path to the current runtime scala.
Different scripts can specify different versions of scala via the hashbang line, so environment variables can't be relied on. See #13758
It might not matter for non-script code, although it can be useful there as well.

[bishabosha]

I've had a look and we can check if the property coursier.mainJar is set, which will be the path of the coursier launcher script - we can then use that to set scala.home to the parent directory. - problem here is that using the native script then scala is at s"${sys.props("scala.home")}/bin/scala", but for coursier it is s"${sys.props("scala.home")}/scala" (we could go one directory above to preserve /bin but I think this won't work on a custom Coursier install dir. [edit: I checked and for windows the default it also in some /bin directory])

[bishabosha]

Idea from @sjrd it could likely be much more useful to provide properties that have the classpath of the scala compiler and scala standard libraries, that can be provided as arguments to the java command, this is more uniform than a fragile directory structure that depends on the package manager.

[philwalk]

I like this suggestion, it would then be possible to find the first scala3-library*.jar in the classpath, and two directories up would be scala.home.

[bishabosha]

@philwalk I've added again a minimal version of the changes to run the shebang scripts on macOS - but I would need advice on if this is a problem for testing unglobClasspath.sc

Edit: moved to #15241

[sjrd]

I don't know about the changes with #!/usr/bin/env -S bin/scala, but otherwise LGTM.

[bishabosha]

for clarification: jline is included in the compiler toolchain by dist/bin/common, so the -classpath 'dist/target/pack/lib/*' is not necessary. However Jsoup is in the lib directory, making the import break without it.

[bishabosha]

I will open a new PR with the shebang changes (Edit: see #15241)

[philwalk]

Looks good

[bishabosha]

do you think we can backport this to the 3.1.3 branch? - It would be good to get this as soon as possible into Coursier's scalac script