A useful function to contribute to Scala Metals lsp server with Emacs

I am in the process of contributing a feature to Scala Metals LSP server. The change is about adding a code action to stub functions/methods after declaring their usagen.

Anyway, it was nice I could focus on the change because I could add tests and run my code against them to see progress.

Naturally tests are never exhaustive. As soon as I ran my enhanced version of Metals locally, I found out my code action wouldn't work. There I go at debugging with println.

The pain I felt was reinstalling my latest version of Metals each time: add a println, reinstall, try again, fix code and repeat. The reinstall bit also consisted in multiple steps:

1. sbt publishLocal
2. (first time only) sbt ++2.13.15 mtags/publishLocal
3. install snapshot via coursier as explained in the vim section
4. restart metals in my Scala buffer

I got soon tired and added the following to my Emacs configuration:

(defun my/reinstall-metals-snapshot ()
    "Reinstall metals from snapshot created with sbt publishLocal. TODO: edit this function with the right version."
    (interactive)
    ;; (shell-command "cd your-metals-path; sbt publishLocal")
    (call-process
     (lsp-package-path 'coursier)
     nil
     (get-buffer-create "*Coursier log*")
     t
     "bootstrap"
     "--java-opt"
     "-Xss4m"
     "--java-opt"
     "-Xms100m"
     (concat "org.scalameta:metals_" lsp-metals-install-scala-version ":" "1.4.1-SNAPSHOT")
     "-o"
     lsp-metals-metals-store-path
     "-f")
    (with-demoted-errors "%S"
      (funcall-interactively 'lsp-workspace-restart (lsp--read-workspace)))
    )

I left out the publishLocal step because it is quicker running sbt and interactively publish the snapshot. Also I quickly hacked this, so I just hardcoded the snapshot version I needed.

Anyway that saved a lot of time in fixing the issues I found interactively. I may end up writing about tips to contribute to Metals later, if anybody is curious.

Happy contributing!