C: lua runner tests regressed (segfault on most scripts)

Type: bug (C frontend / runtime regression) — Track C
Status: done
Owner: Codex
Found / Opened: 2026-06-28, noticed while verifying the crtl auto-pull change ([[c-linking-and-crtl-autopull]]).

Symptom

make test-lua fails: of the lua scripts only oop.lua passes; closures.lua, coroutines.lua, strings.lua segfault the runner, and files.lua / numeric.lua produce wrong output.

Pre-existing, not the auto-pull change

Confirmed identical failures on the compiler built from d320278b (the commit BEFORE the crtl auto-pull work) — the auto-pull is byte-neutral for lua (no impl is auto-pulled; runner.c's explicit #include "*.c" unity build is deduped, output binary is identical). So lua regressed at some earlier point.

test-lua is not part of make test (the default gate is test-core test-debug-g lib-fpc-clean), which is why the regression drifted in unnoticed.

Notes / leads

Memory records lua as previously FUNCTIONAL (control flow, closures, coroutines, metatables, string methods, table.sort, pcall) — see the M5 lua bring-up notes. So a compiler change between then and now broke it.
The passing case (oop.lua) vs the segfaulting ones (closures, coroutines, strings) suggests something in closures / upvalues / coroutine stack / string interning — bisect compiler commits against make test-lua to localise.
Consider adding test-lua (and a sqlite smoke, once it runs) to the gate so C bring-up regressions are caught.

Acceptance

make test-lua green again (all scripts match expected).
Root-cause commit identified; regression test added to the standard gate.

Log

2026-06-29: Moved to working. Reproducing make test-lua failures and reducing the crash/wrong-output cause.
2026-06-29: Done. Root cause was C #if evaluation expanding object-like macros recursively but not function-like macro calls. Lua's L_INTHASBITS(SIZE_Bx) therefore evaluated false, MAXARG_Bx fell back to INT_MAX, and Lua bytecode immediates decoded as values like 0xC0000002. Added function-like macro expansion in #if, restored make test-lua, and wired reduced Lua-shaped C regressions into test-core.