Profiles

Profiles in Factorio.toml control transpile behaviour. They are not Cargo [profile.dev] / --release profiles.

Keys

Under [profiles.<name>]:

Key	Meaning
`debug_level`	Lua comment verbosity (`0` = headers only; `1+` adds more inline comments)
`prune_dead_code`	Remove unreachable IR before codegen
`optimize_ir`	Rewrite IR for cheaper / more readable Lua (IIFE hoist, closure inline, …)

Defaults

Profile name	Default `debug_level`	Default `prune_dead_code`	Default `optimize_ir`
`debug`	`1`	`false`	`false`
anything else (including `release`)	unset (no debug-comment mode) unless TOML sets it	`true`	`true`

Init templates and examples usually set release to debug_level = 0 explicitly.

What `optimize_ir` does

After optional pruning, release builds run IR passes that:

Expand statement-context and mid-expression if / empty IIFEs into real if/else (temps like __hN for call args and binops; never Lua and/or)
Simplify locals: Option/Result unwrap_or, bool if->expr, not not / comparison negation folds, __... copy-prop (idents/literals freely; field loads and impure values only for a single straight-line use so hoisted self.tag stays bound), nil-init collapse, identity pattern binds, flag == true -> truthiness
Inline trivial single-use closures (e.g. |n| n + 1 in .map), then simplify again so inlined shapes get the same folds
Flatten nested string concatenations from format! / asserts (drop empty "" parts)

Frontend also fuses option.ok_or(e)? so the Ok path skips a Result table.

Codegen emits elseif for nested else-if chains, shares { __index = Type } metatable locals for types with methods, and skips setmetatable on method-less enums.

These reduce Lua 5.2 CLOSURE / CALL / NEWTABLE / MOVE traffic versus naive IIFE emission. When investigating a hot helper, luac -l (Lua 5.2) on the emitted chunk is a useful before/after check; Factorio’s opcode list matches stock 5.2.

CLI defaults

Command	Default `--profile`
`build`, `install`	`debug`
`package`	`release`
`check`	(no profile; lints come from `[lints]`)

Override emit profiles with --profile <name> and/or --debug-level N on build / package / install.

What pruning keeps

Reachability starts from:

#[factorio_rs::event] handlers
#[factorio_rs::export] functions (cross-mod API must survive even if unused in-mod)
public structs and enums in shared stage modules (library require() surface)
public functions and structs (and enums) in settings/data stage modules (load-time entry points)

Everything else is kept only if referenced from those roots. Prefer passing function values (or lua_fn(...)) into Factorio APIs instead of stringly callback names when prune is on - otherwise the handler can be deleted.

Config reference: Factorio.toml.