chore(devshell): add a Nix flake dev environment - #409
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nix develop provides stable + nightly Rust via rustup proxies linked to pinned rust-overlay store paths, plus node/yarn/bun, wasm-pack, binaryen, cargo-deny, git, pkg-config. Committed flake.lock pins nixpkgs and rust-overlay for reproducibility. Toolchains are symlinked under the official channel directory names in RUSTUP_HOME instead of custom names: rustup >= 1.28 rejects channel-like custom names, and rustup resolves +stable/+nightly as named channels in any case, so this is the only way those dispatch to the pinned store paths without network downloads. Manifest-dependent introspection (rustup show, rustup target list --toolchain <channel>) errors on read-only store-linked toolchains; use rustup toolchain list / rustc +<channel> --version instead.
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Summary
nix developnow drops you into a reproducible TrUAPI dev shell with the exact toolchain versions the repo needs — no ad-hoc rustup installs. The flake pins nixpkgs (nixos-unstable) and supplies stable + nightly Rust via rust-overlay, with the stable toolchain carrying thewasm32-unknown-unknowntarget. The shell also provides nodejs 22, yarn, bun, wasm-pack, wasm-bindgen-cli, binaryen, pkg-config, and cargo-deny.Toolchains are pinned as flake inputs rather than resolved by rustup, so every machine (and CI) gets identical compiler versions. The shell hook links the pinned store paths into
RUSTUP_HOME/toolchainsunder the channel names, socargo +stable/cargo +nightlykeep working and dispatch to the pinned toolchains instead of triggering a network download. Known tradeoff: linked toolchains carry no dist manifest, so manifest-dependent introspection (rustup show,rustup target list --toolchain <channel>) errors;rustup toolchain list,rustup show active-toolchain, andrustc +<channel> --versionare unaffected.Validation
nix flake check --no-buildpasses — the flake evaluates cleanly. Toolchain store builds were not realized in this run;nix developshould be exercised in CI before merge.flake.lockis committed, pinning nixpkgs, rust-overlay, and flake-utils revisions.New concepts
rust-overlay toolchains dispatched through rustup links
rustup normally downloads toolchains on demand; a flake wants them pinned in the Nix store.
rust-overlayprovides the pinned toolchains as derivations, butcargo +stable/cargo +nightlydispatch resolves through rustup'sRUSTUP_HOME/toolchains/<channel>-<triple>directories — a path rustup manages and would happily replace with its own download. The shell hook bridges the two: it symlinks the store paths into those channel directories before rustup can interfere. Use this when a repo needs channel-style dispatch (+stable,+nightly) against hermetic toolchains; skip it when the repo is fine calling the toolchain binaries directly or managing versions through rustup alone.