Option -save is not supported

[julienrf]

Is your feature request related to a problem? Please describe.

The current scala runner (based on Scala 2.13) does support a -save option.

The experimental scala runner (based on Scala CLI) does not recognize that option:

$ scala -save test.scala 
Unrecognized argument: -save

To list all available options, run
  /home/julien/.local/share/coursier/bin/.scala.aux --help

Describe the solution you'd like

For the sake of compatibility with the current runner, it would be great to recognize the -save option. As far as I understand, Scala CLI now always behaves like the current scala -save, so the option is not necessary anymore. Therefore, it could simply print a warning like “Unnecessary option: -save. This option is always enabled.”

[Gedochao]

As far as I understand, Scala CLI now always behaves like the current scala -save, so the option is not necessary anymore.

Actually, it seems that part isn't entirely true.
There doesn't seem to be any official docs on the -save (and tied -nosave) options for the old scala command beyond what's in the runner code itself.
For context, here are the relevant code bits:

• Scala 2: https://github.com/scala/scala/blob/f8d3c4d57854f08ae261b65d87005de004e8b2c8/src/compiler/scala/tools/nsc/GenericRunnerSettings.scala#L60
• Scala 3: https://github.com/lampepfl/dotty/blob/main/compiler/src/dotty/tools/MainGenericRunner.scala#L142

Looking at the actual behaviour:

▶ tree -a
# .
# └── smth.scala
#
# 0 directories, 1 file
▶ scala -save smth.scala
# Hello
▶ tree -a
# .
# ├── smth.jar
# └── smth.scala
# 
# 0 directories, 2 files
▶ scala smth.jar
# Hello

It seems that the -save option forces a compiled jar to be saved in the cwd, while -nosave overrides it and prevents the jar being saved (for whatever reason).

Now, this looks like a way to combine the run and package --lib subcommands of Scala CLI.
We could theoretically support it by running the 2 subcommands one after another (that'd be a quick bandaid) or (preferably) combine both effects in a single build.

Therefore, it could simply print a warning like “Unnecessary option: -save. This option is always enabled.”

In this context, that wouldn't be true. We could always just not support it if it's not actually needed and print a warning like Deprecated option '-save' ignored., so that it doesn't fail the build.

@julienrf thoughts? Is this option necessary?

[Gedochao]

Also, a side note - it seems that what I mentioned above would also require us to implement #1641, so I'm tagging it as SIP as well...

[julienrf]

I think the fact that it saves the compiled code as a .jar is an “implementation detail”. But maybe not. Maybe some people are relying on the produced jar. In that case, I think a warning saying that this option is ignored but the compilation artifacts are saved (in .scala-build/) for reuse, and that a .jar can be produced with the command package would be enough.

[Gedochao]

We could even suggest running a subsequent package --lib in the warning, too, in case someone actually needs that jar... That'd reuse whatever is in .scala-build/, so it wouldn't be much slower beyond the necessity of running another command.
I guess that if it's a niche use case, maybe that'd be enough.