devenv-fleet

The FastTrackStudios fleet's shared devenv modules and pins. Every fleet Rust repo imports them, so each dev shell, each CI job and each release build compiles with one rustc store path, one gcc, mold and glibc, and kache shares their builds across repos.

Written for devenv 2.4.0.

Module	What it gives a repo
rust	The fleet toolchain (lib/toolchain.nix: rust-overlay's rust-bin.stable."1.99.1" with rust-src, rust-analyzer, clippy, rustfmt and wasm32), mold as the linker, cargo-hakari, prek, cargo-rail, just, RUST_SRC_PATH, a fleet-doctor script, and prek's hooks in repos with a prek.toml
dioxus	The fleet's one dx (the Brahmastra-Labs fork plus pkgs/dx-no-rustc-wrapper.patch, DX_NO_RUSTC_WRAPPER=1), binaryen, wasm-bindgen-cli, tailwindcss and the wasm32 C toolchain
telemetry	devenv up runs a local Teley on :8787 (the room in ~/.teley/session.json, which Claude's Teley MCP subscribes to) and an OpenTelemetry Collector on :4318 that batches and forwards to it
darwin	iOS and macOS: xcrun linker wrappers, IPHONEOS_DEPLOYMENT_TARGET, DYLD_LIBRARY_PATH. Inert on Linux

pins.json is the one source of truth for the revisions: nixpkgs, rust-overlay, nixpkgs-dx, the dx fork, Teley, the rustc store path each system should get, and the devenv that CI bootstraps.

Importing it

On 2.4.0 a remote import's own devenv.yaml is not evaluated, so each module is a devenv.nix only and the importing repo declares the inputs. A repo's devenv.yaml:

require_version: ">=2.4.0"
strict_ports: true            # with `telemetry`: 8787 and 4318 never move
inputs:
  nixpkgs:
    url: github:NixOS/nixpkgs/<pins.json nixpkgs.rev>
  rust-overlay:
    url: github:oxalica/rust-overlay/<pins.json rust-overlay.rev>
    inputs:
      nixpkgs:
        follows: nixpkgs
    overlays:
      - default
  nixpkgs-dx:                 # with `dioxus` only
    url: github:NixOS/nixpkgs/<pins.json nixpkgs-dx.rev>
  devenv-fleet:
    url: github:FastTrackStudios/devenv-fleet/v0.1.1
    flake: false
imports:
  - devenv-fleet/rust
  - devenv-fleet/dioxus      # optional
  - devenv-fleet/telemetry   # optional
  - devenv-fleet/darwin      # optional

Then the repo's own devenv.nix adds its libraries, env and processes.

Don't write the revisions by hand. From a checkout of this repo at the tag you want:

scripts/fleet-pins --write /path/to/repo   # rewrite devenv.yaml, then devenv update
scripts/fleet-pins /path/to/repo           # check devenv.yaml, devenv.lock and flake.lock; exit 1 on drift

A repo that keeps a packaging flake.nix takes the same pins from this repo's flake.nix: inputs.devenv-fleet.url = "github:FastTrackStudios/devenv-fleet/<tag>", nixpkgs.follows = "devenv-fleet/nixpkgs", rust-overlay.follows = "devenv-fleet/rust-overlay", and devenv-fleet.lib.toolchainFor pkgs for the toolchain.

Rules

• .envrc must load devenv's direnvrc before use devenv. A bare use devenv fails with use_devenv: command not found, and in an agent shell that error is silent, so the agent falls back to whatever rustc is on the host PATH:

  eval "$(devenv direnvrc)"
  use devenv

• Never use devenv's dotenv (dotenv.enable). It copies the whole .env file, secrets included, into the Nix store. Load .env with direnv's own dotenv_if_exists .env, after use devenv, and in a process with set -a; [ -f .env ] && . ./.env; set +a.

• Don't let devenv pick the linker. The rust module sets languages.rust.clangLinker.enable = false. devenv's Linux default passes --ld-path=ld.lld, which silently replaces the mold that .cargo/config.toml's -fuse-ld=mold asks for. Don't set languages.rust.rustflags or mold.enable either: RUSTFLAGS replaces the fleet's .cargo/config.toml rustflags tables.

• kache is the host's. When kache is on PATH and RUSTC_WRAPPER is unset, the rust module's shell exports RUSTC_WRAPPER as kache's path. A host that sets RUSTC_WRAPPER itself (THEBATTLESHIP's runners) or kache as cargo's build.rustc-wrapper keeps its own. Never unset RUSTC_WRAPPER in a shell.

• One cargo-hakari. pins.json pins it (cargo-hakari.version); the rust module fails to evaluate if the pinned nixpkgs carries another. CI installs that version (taiki-e/install-action with cargo-hakari@<version>).

• Extra Rust targets change the rustc path. fleet.rust.extraTargets belongs in a profile (profiles.mobile.module), not the default shell.

• The OTLP env goes to processes only. Merge config.fleet.telemetry.processEnv into a process's env; the shell gets none, so tests export nothing.

Checking a shell

devenv shell -- fleet-doctor   # rustc path (exit 1 if not pins.json's), kache wrapper, linker

CI

On a runner without devenv, take the pinned one (it is on cache.nixos.org):

nix build --no-link --print-out-paths "github:NixOS/nixpkgs/$(jq -r .devenv.nixpkgs pins.json)#devenv"

then run steps as devenv shell -- bash -e {0}.

Licence

MIT OR Apache-2.0, at your option (LICENSE-MIT, LICENSE-APACHE).