Serde / JSON

factorio-rs can lower serde_json encode/decode calls to Factorio builtins. There is no serde runtime in Factorio; this is transpile-time rewriting, like Tracing.

Enable the feature

In your mod’s Cargo.toml:

[dependencies]
factorio-rs = { version = "0.3.0", features = ["serde"] }

That pulls in serde and serde_json so derives and calls type-check under cargo check. Re-exports:

use factorio_rs::prelude::*; // Serialize, Deserialize
use factorio_rs::serde_json;

#[derive(Serialize, Deserialize)]
struct SaveData {
    tick: u32,
}

The CLI lowers these calls by default (factorio-rs-cli feature serde).

What lowers

Rust	Lua
serde_json::to_string(v) / to_string_pretty(v)	helpers.table_to_json(v)
serde_json::from_str(s)	helpers.json_to_table(s)
serde_json::to_value(v) / from_value(v)	v
serde_json::to_vec(v)	string.pack("s", helpers.table_to_json(v))
serde_json::from_slice(b)	helpers.json_to_table(string.unpack("s", b))

Binary uses Lua’s size-prefixed "s" format on Factorio’s string.pack / unpack. Prefer .unwrap() / .expect(...) on Result so types match real serde usage under cargo check - the transpile strips those calls (and may lint). For fallible gameplay code prefer ? / if let Ok - see Option and Result.

#[derive(Serialize, Deserialize)] is typecheck-only - the transpiler never runs serde; struct values are already Lua tables. Use this when you need JSON for debugging or a remote payload, not as a general Rust serde runtime.

Not supported: serde_json::json!, streaming serializers, and other APIs.

Feature matrix

Crate	Feature	Role
factorio-rs	serde	Optional serde + serde_json deps + prelude re-exports
factorio-rs-cli	serde (default)	Enable frontend lowering when building mods
factorio-frontend	serde	Implementation of the call lowering