crtl: fopen/fclose/fseek/ftell declared but not defined (no file open)

• Type: bug / feature gap (lib/crtl — Track B, library implementation)
• Status: done
• Found / Opened: 2026-06-27 (Track A+C, while building the make test-lua suite — the runner had to read the program from stdin because there is no way to open a file)
• Track note: the cfront compiler (clexer/cparser/cpreproc, C→IR) is Track C, but implementing crtl library functions (fopen, string/io routines) is library-author work = Track B, same as writing lib/rtl or lib/pcl. Grey area, but filling in a runtime function body belongs to B.

Symptom

lib/crtl/include/stdio.h declares fopen, fclose, fseek, ftell (and unistd.h declares lseek), but none are defined in lib/crtl/src. Only the descriptor-based stream calls exist — fread/fwrite/fputs/fgetc/feof ride __pxx_read/__pxx_write on an already-open fd.

Calling fopen therefore links to a dynamic libc import (or returns a bogus FILE*); the crtl fread then reads stream->fd from a layout that is not libc's FILE, so the read fails:

FILE *f = fopen("x.lua", "rb");   /* non-null, but not a crtl FILE */
fread(buf, 1, n, f);              /* reads garbage fd -> fails */

Impact: any C program that opens a file (lua io.open/dofile, config readers, the natural make test-lua runner) cannot. The lua suite works around it by feeding the program on stdin (__pxx_read(0, …)), and liolib.c's file API is effectively dead.

Fix direction — matches the existing stdio PAL bridge

The Pascal RTL already has a real syscall file-open: PalOpen(path, flags, mode) in lib/rtl/platform.pas (used by textfile.pas / sysutils.pas / dns.pas). The C stdio bridge already binds __pxx_write/__pxx_read to PalWrite/PalRead via the shared-Procs/FindProc mechanism (see the project_c_stdio_pal_bridge_done arc). Extend the same way:

1. Add a thin __pxx_open(const char *path, int flags, int mode) / __pxx_close(int fd) bridge to PalOpen/PalClose (pxxcio.pas).
2. Define crtl fopen (map "r"/"w"/"a"/"+"/"b" → PAL flags, allocate a FILE with the returned fd), fclose (__pxx_close + free), and the seek family (fseek/ftell/lseek → a PalSeek/lseek syscall bridge; add one if the RTL lacks it).
3. Then the make test-lua runner can fopen the .lua path directly instead of reading stdin, and lua io/dofile come alive — basis for the lua-sqlite desktop milestone (feature-c-desktop-lua-sqlite-path).

Gate: a crtl C test that writes a temp file, reopens it, reads it back; plus make test-lua still green.

Log

• 2026-06-27 — Implemented in working tree (commit pending): pxxcio now bridges __pxx_open/__pxx_close/__pxx_seek/__pxx_remove/__pxx_rename to PAL; lib/crtl/src/stdio.c defines fopen/freopen/fclose/fseek/ftell/ rewind, POSIX read/write/close/lseek, remove/rename, a small static stream pool, and a minimal errno. Regression: test/cfile_stdio_b87.c writes, seeks, reopens, reads, rewinds, closes, and removes a temp file. Verified with /tmp/pascal26-build -Ilib/crtl/include -Ilib/crtl/src test/cfile_stdio_b87.c /tmp/cfile_stdio_b87_build && /tmp/cfile_stdio_b87_build returning 42.