Case-sensitive C header lookup mismatch on Linux

• Type: bug
• Status: done
• Track: A (compiler frontend)
• Owner: Codex
• Opened: 2026-06-28

Motivation

Currently, when a Pascal program attempts to import a capitalized C header (such as uses Lerc_c_api;, uses FreeImage;, or uses GraphBLAS;), the lookup fails with uses: unit source not found: lerc_c_api.

This happens because:

1. The compiler converts unit names to lowercase when searching for files on disk (e.g. lo := LowerCase(name); in CHeaderStem inside compiler/parser.inc).
2. Linux filesystems are case-sensitive. Thus, the compiler tries to open lerc_c_api.h but fails to find the actual Lerc_c_api.h file on disk.

To make header import seamless, the lookup mechanism should resolve the casing mismatch gracefully.

Scope

1. Case-Tolerant Lookup:
   • Update file-loading and unit-resolution routines in the compiler (such as ParseUsesUnit or LoadFile wrapper paths) to fallback to a case-insensitive search if a file lookup fails.
   • When a case-insensitive match (e.g., matching Lerc_c_api.h for lerc_c_api.h) is found in the search directory, use that file.

Acceptance

• Capitalized system headers (such as uses Lerc_c_api;, uses FreeImage;, and uses GraphBLAS;) compile and import successfully on Linux without requiring manual renaming.

Log

• 2026-06-29 — Added a case-insensitive load fallback for Pascal unit and C header resolution.
• 2026-06-29 — Narrowed the fallback to Pascal source/unit lookup only. C header and C preprocessor includes remain exact-case by design to avoid ambiguous header imports. Verified uses uPSUtils finds uPSUtils.pas through -Fu, exact-case header import still works, and make test-core passes.
• 2026-06-29 — Picked up on Track A. Reproduced the Pascal unit side with uses uPSUtils failing to find uPSUtils.pas because the resolver probes upsutils.pas on Linux.
• 2026-06-28 — bug ticket opened.
• 2026-06-28 — confirmed also affects Pascal unit lookup, not just C headers. uses uPSUtils fails with unit source not found: upsutils because the compiler lowercases the name before the filesystem lookup. RemObjects Pascal Script (all uPS* units) is blocked by this on Linux. The fix is the same: case-insensitive fallback in the Pascal unit resolver path (ParseUsesUnit), not only in CHeaderStem.