Scripting solution

[anatoliykmetyuk]

This PR adds scripting support to Scala 3. Given a source named Test.scala:

@main def Test(name: String): Unit =
  println(s"Hello ${name}!")

You can run: ./bin/scala ../playground/foo/Test.scala World to get an output Hello World.

Internally, scala detects the first residual argument which ends with *.scala. It then assumes it to be a file that the user wants to run as a script, and all the arguments after that file are treated as the arguments to that script.

A "script" is an ordinary Scala file which contains a @main method. The semantics of the scala Script.scala command are as follows:

• Compile Script.scala with scalac into a temporary directory
• Detect the main method in the *.class files produced by the compilation
• Execute the main method reflectively

[nicolasstucki]

We are also missing some docs.

[philwalk]

I have used scala for several years, and make heavy use of scala scripting. I am eager to contribute to this and have some ideas to greatly improve the user experience for new users.

[som-snytt]

This will make it much easier to run quick test comparisons between Scala 2 and 3!

[rjolly]

I have a dream that scala is just a shorthand for

jrunscript -cp lib/scala3-compiler_3.0.0-M3.jar:lib/scala3-library_3.0.0-M3.jar:lib/scala3-interfaces-3.0.0-M3.jar:lib/tasty-core_3.0.0-M3.jar:lib/scala-library-2.13.4.jar:lib/scala-asm-7.3.1-scala-1.jar -Djava.class.path=lib/scala3-library_3.0.0-M3.jar:lib/scala-library-2.13.4.jar -l scala