.bsp/scala-cli not updating when scala-cli is upgraded

[kubukoz]

Moved from VirtusLab/scala-cli#4201.

Describe the bug

The Nix package of scala-cli provides a wrapper script, but ultimately the scala-cli binary is located in a versioned path in Nix Store, e.g. /nix/store/flpc752pnb8qk0wljdivj8nfdkfxgv76-scala-cli-1.12.2/bin/scala-cli. It creates .bsp files like this:

{
  "name": "scala-cli",
  "argv": [
    "/nix/store/flpc752pnb8qk0wljdivj8nfdkfxgv76-scala-cli-1.12.2/bin/scala-cli",
    "bsp",
    "--json-options",
    "/Users/kubukoz/projects/demos/.scala-build/ide-options-v2.json",
    "--json-launcher-options",
    "/Users/kubukoz/projects/demos/.scala-build/ide-launcher-options.json",
    "--envs-file",
    "/Users/kubukoz/projects/demos/.scala-build/ide-envs.json",
    "/Users/kubukoz/projects/demos"
  ],
  "version": "1.12.2",
  "bspVersion": "2.1.1",
  "languages": [
    "scala",
    "java"
  ]
}

However, these don't get updated when scala-cli gets upgraded. As a result, once I upgrade scala-cli, existing projects won't work in Metals until I manually remove the BSP config file.

To Reproduce

1. Install an older scala-cli via Nix
2. Import a build into Metals
3. Upgrade scala-cli
4. java.io.IOException: Cannot run program "/nix/store/flpc752pnb8qk0wljdivj8nfdkfxgv76-scala-cli-1.12.2/bin/scala-cli" (in directory "/Users/kubukoz/projects/demos"): Exec failed, error: 2 (No such file or directory)

Expected behaviour

Metals should regenerate the .bsp/scala-cli.json file (or at least detect the stale path and offer to fix it) when the scala-cli binary path no longer exists.

Suggested solution

As suggested by @tgodzik, Metals could detect that the binary referenced in .bsp/scala-cli.json no longer exists and regenerate the file.

[kubukoz]

cc @Gedochao