{$I+} / {$IOCHECKS ON}: raise on Text I/O failure

• Type: feature (FPC-parity runtime checks). Track A (+ textfile RTL).
• Status: done
• Opened: 2026-07-15 night, straight after {$R+} completed — the probe:

{$I+} assign(t,'/nonexistent/dir/f'); reset(t);   { FPC: EInOutError }

FPC 3.2.2: caught=1 (and {$I+} is FPC's DEFAULT). pxx: reset silently no-ops (IOResult reports it, {$I-} style — pxx currently behaves as permanently {$I-}).

Design (the {$Q+}/{$R+} pattern, with one twist)

• Directive family: {$I+}/{$I-} single-letter (mind the {$I file} include form — same disambiguation dance as {$R}), {$IOCHECKS ON/OFF}, per-token TokIChecks, statement-anchored.
• TWIST vs Q/R: the IO ops are ORDINARY RTL CALLS (textfile.pas Reset/Rewrite/Append/Close/Erase + TextWrite/TextWriteLn/TextReadLn) — there is no single IR op to tag. Emit the check at the CALL SITE: when a statement-position call resolves to one of those procs (and the text read/write rewrites in ParseTextWriteRest/ParseTextReadRest), sequence a PXXIoCheck call after it. PXXIoCheck (textfile or builtinheap): if LastIOResult <> 0 then hook-raise EInOutError (4th hook, PXXIoErrorHook installed by sysutils) else 'Runtime error <code>' — FPC halts with the IO code itself as the runtime-error number.
• IOResult must still CLEAR on read per FPC semantics — check interaction with the existing SetIO/LastIOResult machinery (textfile.pas).

DIALECT-DEFAULT QUESTION (user call — do not decide unilaterally)

FPC defaults to {$I+}; pxx today behaves {$I-} everywhere. Options: (a) keep pxx-lax default (quiet, IOResult-style) with {$I+} opt-in — matches the meta-dialect contract's lenient-default rule; (b) flip to FPC's default under --mimic-fpc only; (c) flip globally (would change failure behavior of every existing program/demo silently — riskiest). Recommend (a)+(b). Cf. the float-exception-mask decision where the user explicitly chose quiet-by-default (feature-float-exception-mask-control).

Acceptance

• The probe matches FPC with {$I+} regions; {$I-}/default keeps today's IOResult behavior (per the user's dialect call).
• Hook family test extended; conformance sweep stays green.

Log

• 2026-07-15 — resolved, commit 8135f170.