Add Playground to make debugging easier in Metals

[adpi2]

1. Bump junit-interface to 0.13.3
   This is needed by Metals to have the test explorer working (source)

2. Add Playground class in scala3-compiler-test to make debugging easier
   It contains an example test that check the compilation of the tests/playground/example.scala file.
   The Playground class is annotated with @org.junit.Ignore: you need to remove it to run the test.

Demo:

[bishabosha]

when I try what's in the gif, my user dir is dotty/compiler so the path tests/playground/example.scala can't be found, I wonder why this is :/

[adpi2]

@bishabosha Could it be that you use Bloop and that Bloop does not take into account the working directory setting defined here:
https://github.com/lampepfl/dotty/blob/5fcfeeceeddaa0193c566f2dcf7d12ed279dfce8/project/Build.scala#L534

I don't think there is an easy fix for this. Maybe you can use sbt as the build server?

[adpi2]

@bishabosha Or you can change the Playground test itself locally:

compileFile("../../tests/playground/example.scala", defaultOptions).checkCompile()

[bishabosha]

I don't think there is an easy fix for this. Maybe you can use sbt as the build server?

I switched to sbt as the build server and then it worked as expected. Thanks!

[mbovel]

Excellent! I'll make a separate PR to document this.