`hx --grammar fetch` fails when using Helix built with Nix

[AumyF]

Summary

helix --grammar fetch fails when using Helix built with Nix, since its runtime directory is set in Nix store which is not writable.

Reproduction Steps

1. nix shell github:helix-editor/helix
2. hx --grammar fetch

Helix log

Error: Failed to fetch some grammar(s)

Caused by:
    0: Could not create grammar directory "/nix/store/5znz3zwidqndnqa54ibhv1yfgxd5xmip-helix-runtime/grammars/sources/protobuf"
    1: Permission denied (os error 13)

Platform

Arch Linux

Terminal Emulator

foot 1.12.1

Helix Version

helix 22.05

[archseer]

There's a previous issue for this but it was closed: #2091 (comment)

[the-mikedavis]

You don't need to use hx -g fetch when using the Nix flake, grammars are fetched and built by nix when building hx. The runtime for nix is in the store which is immutable, so hx -g fetch and hx -g build fail.

I don't think there's an issue for it yet but like archseer says in the linked commit, we want to treat the runtime directory from installation (usually into /usr but /nix/store for nix) as immutable and have ~/.config/helix or other XDG dirs act as overrides like it does currently for configuration files like languages.toml

[tgharib]

hx --health to confirm highlighting (from treesitter) is working

[the-mikedavis]

I'll close this out as expected behavior but I've opened up #3346 describing how we'd like to do this in the long-run. With a solution to that, hx -g fetch/hx -g build should act on ~/.config/helix/runtime rather than the Nix store.