Builtin write/writeln matched case-sensitively (only lowercase resolves)

• Type: bug (compiler)
• Status: backlog
• Owner: — (track A)
• Opened: 2026-06-19 (discovered by Claude B: examples/adventure)

Symptom

User-defined identifiers are case-insensitive (the documented default — see defs.inc:610 "standard case-insensitive Pascal"; FOO resolves to Foo). But the builtin I/O intrinsics only match the exact lowercase spelling:

writeln;        -> OK
WriteLn;        -> pascal26: error: undefined variable (WriteLn)
Writeln(7);     -> pascal26: error: undefined variable (Writeln)
WRITELN(7);     -> pascal26: error: undefined variable (WRITELN)

examples/adventure/engine.pas:228 (WriteLn;) fails for this reason. Likely affects write / read / readln too, and possibly other intrinsics matched by a hardcoded lowercase string compare rather than the case-insensitive symbol path.

Impact

Blocks any FPC-idiomatic demo that uses mixed-case Write/WriteLn/ReadLn (common in real Pascal). Track B cannot fix from lib/** — the intrinsics are recognized in the compiler, not the RTL.

Direction

Resolve builtin intrinsic names through the same case-insensitive matcher used for ordinary identifiers (respecting CaseSensitiveMode when the {$CASESENSITIVE ON} directive is active). Add a test covering WriteLn / Write / ReadLn mixed case.

Log

• 2026-06-19 — opened by track B while advancing the adventure demo (after IntToStr + Copy/Trim landed, this is the next blocker before the Text-file I/O gap).

Resolution (2026-06-19) — DONE (commit 3de5d05)

The four I/O intrinsics (Write/WriteLn/Read/ReadLn) now match case-insensitively in the lexer (via CaseEqual) unless {$CASESENSITIVE ON}, where the exact lowercase spelling still applies. No mixed-case Write/Read identifiers exist in the compiler source (verified) so self-host stays byte-identical. test_case_io in test-core.