Add support for the `:sh` command in the REPL

[Gedochao]

The :sh command was (and is) supported by the Scala 2 REPL, while it is visibly absent in Scala 3.

scala -S 2.13
Welcome to Scala 2.13.15 (OpenJDK 64-Bit Server VM, Java 17).
Type in expressions for evaluation. Or try :help.
scala> :help
All commands can be abbreviated, e.g., :he instead of :help.
(...)
:sh <command line>       run a shell command (result is implicitly => List[String])
(...)
scala> :sh scala-cli --help
val res9: scala.tools.nsc.interpreter.shell.ProcessResult = `scala-cli --help` (54 lines, exit 0)

scala> res9.lines.mkString(System.lineSeparator)
val res10: String =
Usage: scala-cli <COMMAND>
Scala CLI is a command-line tool to interact with the Scala language. It lets you compile, run and test your Scala code.

Main commands:
  clean                  Clean the workspace.
  compile                Compile Scala code.
  doc                    Generate Scaladoc documentation.
  fmt, format, scalafmt  Formats Scala code.
  repl, console          Fire-up a Scala REPL.
  run                    Compile and run Scala code.
  test                   Compile and test Scala code.

Miscellaneous commands:
  version  Prints the version of the Scala CLI and the default version of Scala.

Other commands:
  config    ...

[mbovel]

I started looking into this and noticed that the Scala 2 implementation returns a scala.tools.nsc.interpreter.shell.ProcessResult object. scala.tools.nsc mainly seems to contain Scala 2-related things. Would we want to continue using it for a Scala 3 implementation? Are we committed to maintain these APIs?

An alternative that also works outside of the REPL is scala.sys.process:

➜  ~ scala -S 3.6.2
Jan 09, 2025 4:49:11 PM org.jline.utils.Log logr
WARNING: The terminal provider jna has been deprecated, check your configuration. This warning can be disabled by setting the system property org.jline.terminal.disableDeprecatedProviderWarning to true.
Welcome to Scala 3.6.2 (21.0.5, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                
scala> import scala.sys.process.*
                                                                                
scala> "scala-cli --help".!
Usage: scala-cli <COMMAND>
Scala CLI is a command-line tool to interact with the Scala language. It lets you compile, run, test and package your Scala code.
...

What would be the advantage of having a specific :sh REPL command compared to using scala.sys.process?

[SethTisue]

I'd forgotten :sh even exists; I don't recall ever hearing anyone ever mention it.

[mbovel]

What you you think @Gedochao:

• Is it worth investing in :sh when we already havescala.sys.process?
• If we do, should it use scala.tools.nsc.interpreter.shell as the Scala 2 implementation?

[Gedochao]

@mbovel I'll raise it on core today

[tgodzik]

The conclusions is that we should deprecate it in Scala 2, which already has the ticket (above) and Scala 3 should have a proper error message on how to work around the missing feature.

[Gedochao]

The conclusions is that we should deprecate it in Scala 2, which already has the ticket (above) and Scala 3 should have a proper error message on how to work around the missing feature.

@mbovel calling :sh in the Scala 3 REPL should print a warning, informing that it is not supported in Scala 3 and suggesting to call scala.sys.process.Process(_).! directly.