{$I file} misses are silent, and includes only resolve next to the source file

• Type: bug (Pascal frontend — include expansion) — Track P (the expansion pass lives in shared elfwriter.inc / lexer plumbing, so A's gate)
• Status: done
• Opened: 2026-07-11, found on the New-ZenGL Pascal ladder ([[feature-game-library-candidate-suite]] slice C).

Symptom

Two related gaps in {$I name} / {$include name} handling (the pre-lex expansion pass in compiler/elfwriter.inc, LoadFileCI site ~line 2949):

1. Silent miss. When the include file cannot be found, the directive is dropped without any diagnostic. Defines the include would set never happen, so compilation continues with silently different configuration — the worst failure mode. Repro:

   program t;
   {$I does_not_exist.cfg}
   begin end.
   
   

   compiles "ok" today. FPC: Fatal: Can't open include file.

2. No include search path. Includes resolve relative to the including file's directory only. ZenGL keeps zgl_config.cfg in headers/ while the units live in src//srcGL/ (FPC builds pass -Fi<dir>; Lazarus projects set include paths). PXX has no -Fi equivalent, so every zgl unit's {$I zgl_config.cfg} silently vanishes (see gap 1).

Where hit

All of library_candidates/zengl/Zengl_SRC/src/*.pas ({$I zgl_config.cfg} from headers/). Any FPC/Lazarus project with an include directory will hit the same.

Acceptance

• A missing include is a compile error naming the file (matching FPC).
• -Fi<dir> (accept -I<dir> too) adds include search directories; search order = including file's dir, then -Fi dirs in order. -Fu dirs may reasonably be searched as a fallback (FPC does for some cases; decide and document).
• ZenGL units find zgl_config.cfg via -Fi.../headers; a test covers the error and the search order.

Log

• 2026-07-12 — resolved, commit HEAD.