Add Nix Flake devshell + direnv#432
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thebrandonlucas
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Jul 16, 2026
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| channel = "1.83.0" # check ^^^ when changing this | ||
| components = ["rust-analyzer"] | ||
| components = ["rust-analyzer", "llvm-tools-preview"] |
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Support host stripping performed in scripts/build.py
thebrandonlucas
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Jul 16, 2026
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| def rust_target_is_installed(rust_target: str) -> bool: | ||
| result = subprocess.run( | ||
| ["rustc", "--print", "target-libdir", "--target", rust_target], | ||
| check=False, | ||
| stdout=subprocess.PIPE, | ||
| stderr=subprocess.DEVNULL, | ||
| text=True, | ||
| ) | ||
| return result.returncode == 0 and Path(result.stdout.strip()).is_dir() | ||
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| def install_rust_target(rust_target: str, *, required: bool = False) -> None: | ||
| if rust_target_is_installed(rust_target): | ||
| return | ||
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| if shutil.which("rustup") is None: | ||
| message = ( | ||
| f"Rust target {rust_target} is not installed and rustup is unavailable; " | ||
| "enter `nix develop` or install the target manually" | ||
| ) | ||
| if required: | ||
| raise SystemExit(message) | ||
| print(f"warning: {message}") | ||
| return | ||
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| run("rustup", "target", "add", rust_target, check=required) |
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Previously we assumed Rust targets were always managed bu rustup and unconditionally ran this every time, even if the target was already installed. Nix manages this via the nix store and does not use this rustup. So this would fail with rustup: command not found even if all the targets were available. By using rustc to ask where the target libraries should be, then verifying it exists there via result.returncode == 0 and Path(result.stdout.strip()).is_dir(), we maintain backward compat for non-nix users.
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thebrandonlucas
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July 16, 2026 14:33
Restores and updates the old flake.nix to add a post-Zig migration devshell. Also adds direnv for automatic env loading upon entering the directory. Since Zig compiler has no stable release yet, this uses roc-overlay to always use latest nightly roc compiler, so the user doesn't have to continuously download nightly. Adds checks to scripts/build.py to not download the rust toolchain on every build if it already exists, and to allow interop with Nix users and backward compatibility for non Nix users. Also updates CONTRIBUTING.md with new Nix usage section. docs: note required Nix features
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flake.nixwas removed from #413 to avoid bundling another change into that large PR.I've added back the flake.nix as mentioned here removing unnecessary tools and adding new ones (Zig 16, etc.). One problem I ran into was that while the old
flake.nixwas able to just use the standard Roc compiler from unstable nixpkgs, that doesn't work for the new compiler because it's unreleased on nixpkgs. To solve that here we'd have to pin a particular nightly release and just keepbasic-cliup to date with it, modifying the flake with every incompatibility.That seemed like too much overhead to be worth it, and I felt that this must be a general pain point for other projects, so I created roc-overlay to solve this problem for this and other projects that wish to use it. It's modeled after zig-overlay and is useful for any project which intends to keep up with the latest nightly compilers (or pin themselves to previous ones). More here.
Updated
CONTRIBUTING.mdto add the section about using Nix for the development environment. We could probably also take advantage of this to simplify CI (and have a single source of truth) onceroc-overlayproves it's mettle a bit more.I also added direnv which is a great convenience tool for automatically loading dev environments upon shell entry. It requires manual activation by the user once, then subsequently loads the shell with all appropriate dependencies thereafter.