Is your feature request related to a problem? Please describe.

Treefmt is a great tool, but it doesn't take away the burdon of sourcing the used commands.

However, in UX categories, that would be in the ballpark of 50% of additional value (see Devenv, Fleek, Bob, etc).

treefmt-nix doesn't cut the deal, because it requires mental overhead, is not dead simple and interferes with my nix-lib project intent which is not commonly about boilerplate tooling or potentially not a nix project at all.

Describe the solution you'd like

1. Setup and maintenance of CI should be as simple as:

      - name: Install nix
        uses: nixbuild/nix-quick-install-action@v22
      - name: Check formatting
        run: nix run nixpkgs#treefmt -- . --fail-on-change --no-cache

(non-pinning related issues with the tooling formatting are a rare "black-swan" in the horizons of this lifecycle, so we accept them in turn for the 50% additional UX)

1. Set up and usage of treefmt should be as easy as:

• add treefmt.toml
• run treefmt
  • for Nix users which nix, this means feature-flagged (on which nix) profit
  • for no-nix users, this means no deterioration of their current expectations and a pretext to sh <(curl -L https://nixos.org/nix/install), which might be a faster resolution of their problem at hand than any alternative course of action.

Describe alternatives you've considered

treefmt-nix, manual management. It doesn't cut the deal, because it doesn't keep out of my way.

Additional context

I want to do a PR / contribution. Would it be accepted?

nix-community/nix-index-database#44

In Github Actions a hypothetical and arbitrarily pinned nix/nixpkgs could speed up time-to-first-feedback some bits on style checks as it would already have nixpkgs downloaded` and - alas - eval cached.

Potentially, this implementation could attempt to fetch static builds where available to improve the situation further.