gen-langue

name	gen-langue
description	Update Lumo .langue definition files and regenerate the lumo-syntax crate. Use when changing syntax, elab rules, judgments, or the compiler grammar.
allowed-tools	Bash(cargo run *) Bash(bash scripts/verify.sh) Read Edit Write Glob Grep

Langue Definition Update Workflow

The language definition under the repo-root lumo/ directory is the source of truth (D-01); crates/lumo-syntax/src is generated from it by langc. When the definition changes, regenerate.

Workflow

1. Edit the .langue files under lumo/:

   • Lumo.tokens/item/expr.syn.langue — Lumo surface syntax
   • MIR.syn.langue, MIR.type.langue — MIR grammar + judgments
   • JS.syn.langue — the JS emission subset
   • lumo/elab/*.elab.langue — elaboration rules (derived rules, extern rule / extern pass declarations)
   • lumo.langue — the manifest pipe

2. Check, then regenerate:

   cargo run -j 2 -q -p langc -- check lumo
   cargo run -j 2 -q -p langc -- gen lumo -o crates/lumo-syntax/src
   

3. Implement any new externs by hand in crates/lumo-syntax/src/elab_externs.rs (generated Externs traits have no defaults — missing impls fail the build, D-01).

4. Verify — check + gen-freshness + full workspace tests (corpus fixtures included; bless with LANGC_UPDATE=1, which only fills missing expected blocks):

   bash scripts/verify.sh
   

Key rules

• Never edit generated files under crates/lumo-syntax/src (they carry an "Auto-generated by langc gen" header); elab_externs.rs, judge_driver.rs, compile_driver.rs, and tests/ are the handwritten exceptions.
• Generated code is committed (D-21); scripts/verify.sh fails if it drifts from the definition.
• Keep -j 2 — parallel rustc OOMs this machine.
• The legacy workflow this skill used to describe (scripts/gen_langue.sh, crates/compiler/lumo.langue, packages/langue/dist/langue.js) is gone with the Langue 2 rewrite.