Hot reload with Bacon

Use Bacon as the file watcher. factorio-rs exposes jobs Bacon can run - there is no custom factorio-rs watch (open an issue if you would like one).

Install Bacon

cargo install --locked bacon

Scaffold with jobs

factorio-rs init --name my-mod --bacon

Or copy this bacon.toml into an existing project:

default_job = "factorio-reload"
env.CARGO_TERM_COLOR = "always"
# Prefer `dist` over `dist/**` (directory-level notify events).
ignore = ["dist", ".factorio-rs", "target", "src/factorio_exports.rs"]

[jobs.factorio-check]
command = ["factorio-rs", "check"]
need_stdout = true
# Important in Cargo workspaces: default watches include `examples/` recursively.
default_watch = false
watch = ["src", "Factorio.toml", "Cargo.toml"]

[jobs.factorio-reload]
command = ["factorio-rs", "sync", "--symlink", "--hot-reload"]
need_stdout = true
default_watch = false
watch = ["src", "Factorio.toml", "Cargo.toml"]
show_command_error_code = true

[jobs.factorio-test]
command = ["factorio-rs", "test", "--rerun"]
need_stdout = true
default_watch = false
watch = ["src", "Factorio.toml", "Cargo.toml"]
show_command_error_code = true

[keybindings]
c = "job:factorio-check"
r = "job:factorio-reload"
t = "job:factorio-test"

CARGO_TERM_COLOR=always keeps status and test colors when Bacon pipes output. Failure reports use cargo’s ---- name stdout ---- layout so Bacon shows the assertion message instead of italic “no output”.

Hot-reload generation tracks source changes (src/**/*.rs, Factorio.toml, Cargo.toml), not dist/ rewrites. Identical sources print generation N (unchanged) and skip the UDP ping.

If Bacon still loops after a sync, check that jobs set default_watch = false (Bacon’s defaults watch workspace examples/, which includes each example’s dist/).

In-game control reload

Factorio keeps mod Lua in an in-memory VFS for the whole session, so the CLI cannot detect on-disk edits by re-requireing a generation file. Instead:

1. Launch Factorio with localhost UDP enabled (port 34201 by default, override with FACTORIO_RS_UDP_PORT):
   • factorio-rs open / factorio-rs install --open pass --enable-lua-udp=34201
   • Steam: set launch options to --enable-lua-udp=34201
2. Install once and load a save: factorio-rs sync --symlink --hot-reload
3. In another terminal: bacon (default job is factorio-reload) or bacon -j factorio-reload
4. Edit control-stage Rust -> Bacon syncs -> CLI sends a UDP ping -> the in-game probe calls game.reload_mods() (then a second pass automatically).

You should see the world briefly reload when the ping lands (no chat spam).

sync --hot-reload also writes lua/factorio_rs_reload_gen.lua after deploy (for tooling) and injects the UDP probe on control.lua. Prefer --symlink so the mods entry points at dist/ (Unix; falls back to copy).

Data / settings stage: prototype and settings changes still need a full Factorio restart. sync prints a note when those stage files change.

Automated tests without restarting Factorio

bacon -j factorio-test

factorio-rs test --rerun:

1. Builds the suite with a listen-capable harness and hot-reload probe.
2. Starts a headless Factorio listen process if none is running.
3. On later triggers, bumps reload generation, waits for the next suite_end, prints the report, and exits (Bacon-friendly).

Manual equivalents:

factorio-rs test --listen    # keep Factorio alive after the first suite
factorio-rs test --rerun     # rebuild + wait for the next suite

See Testing for the suite protocol and --gui.

See also

• CLI reference - sync, test --listen / --rerun
• First hour - install loop without Bacon
• Stages - control vs data vs settings