Investigate building a Scala 3 plugin

[cb372]

This issue is to investigate the feasibility of porting scala-typed-holes to Scala 3.

I haven't looked at all at how to write compiler plugins in Scala 3. I imagine the plugin architecture is roughly the same, although the AST and the compiler internals are different from Scala 2.

I don't think there's much chance of sharing any code between Scala 2 and Scala 3. I imagine it'll be separate branches, or maybe even separate repos.

[zainab-ali]

I'm working on an initial stab at this in https://github.com/zainab-ali/scala3-typed-holes. I also think the architecture should be roughly the same, and that the challenge will be in tree traversal.

The compiler phases have also changed. I have yet to figure out exactly which phases this runs between.

[cb372]

Great! Thank you for picking this up. Looking forward to seeing how you get on with it.

[zainab-ali]

It's going well so far 🎉
Finding the holes is straightforward.

Here's a working traversal for one binding:
https://github.com/zainab-ali/scala3-typed-holes/blob/main/root/test/resources/sample/expected.txt

The overall structure is a bit clunky (the traversal is split into a prepareFor and transform for pre and post steps. There might be an equivalent of a Traverser somewhere in the dotty codebase that I'm missing. A macro would possibly clean up the syntax.

I've yet to deeply immerse myself in Scala 3 - there may be even more opportunities for holes, and match types will have interesting bindings.

[Mercerenies]

Just here to chime in my support. I found this project just today and would love to see it migrated to Scala 3!