Real-world C programs as compiler stress tests (brainstorm)

Type: idea / test-coverage backlog — Track C+B (C frontend + crtl)
Status: backlog (not scheduled — user prefers moving elsewhere next, e.g. the Nil-Python frontend). Captured because real-world C programs have proven invaluable: lua 5.4 and sqlite3 each surfaced a dozen+ genuine codegen / ABI / crtl bugs that no synthetic test caught (see [[feature-c-cross-lua-sqlite]]).
Opened: 2026-07-05

Why these matter

Big real C programs are the best bug-finders we have. They exercise the C frontend, the crtl syscall/string layer, and the cross-target ABIs under real load. lua + sqlite already run on x86-64/aarch64 (and printf/variadic now work on i386/arm32). Each new program is a fresh discovery→ticket loop. Bonus of C programs specifically: they test the C compiler WITHOUT leaning on our Object-Pascal RTL, so they dodge the FPC-compat RTL / RTTI / library-landmine class of bugs entirely.

Candidates (rated realism × signal)

busybox — 🟢 top pick, applet-at-a-time. Standalone C, no external deps, brutally syscall-heavy → hammers crtl exactly where it is thin. Don't build the whole multi-call binary (obscure headers + CONFIG_* maze); build ONE applet: true/echo/cat/yes are dozens of lines. Green busybox cat = real trophy + fast feedback. Same loop as lua/sqlite.
tcc (Tiny C Compiler) — 🔥 the flex / meta test. A C compiler, in C, famous for compiling itself. Our C frontend builds tcc → tcc builds hello-world = a mic-drop statement about the C frontend's completeness. ~50k lines, mostly self-contained.
p2c — Pascal→C translator, in C (~30k lines). Literally "a Pascal compiler in C" — the buildable stand-in for the gpc idea below.
stb / cJSON / miniz — 🟢 palate cleansers. Single-header C libs, tiny, clean, no syscall jungle. Fast confidence hits; good for shaking out frontend corners quickly.
micropython — Python interpreter in C. Compiled by our C frontend, then it runs Python — while we ALSO have a Nil-Python frontend. Two roads to Python, one compiler. Ambitious.
DOOM — 🎮 the eternal "but does it run DOOM." Source is C; needs a framebuffer / ASCII / headless render shim, but headless perft-style ports exist. Pure clout, one funny thing. Low signal, high morale.

North star (no ceiling)

Compile GCC itself. The ultimate real-world C test — there is no ceiling for this project. Not near-term (GCC is enormous, GMP/MPFR/MPC deps, decades of autoconf), but it is the honest end of the curve, and worth writing down as the aspiration.

gpc note (why it is NOT on the buildable list)

GNU Pascal was raised as a target: a Pascal compiler written in C would test our C frontend and sidestep FPC's RTL/RTTI landmines. Sound reasoning — but gpc is a GCC front-end, welded to GCC's backend/internals, not a standalone program you can compile alone. Use p2c or tcc for the same spirit.

Suggested order (signal per effort, when picked up)

busybox cat (crtl stress — our actually-thin layer)
tcc (frontend-completeness flex)
cJSON / stb (quick corner-shaking)
DOOM (morale)