M2compiler-V3/docs/summary_step3.7.md

V3 step 3.7 — hardening pass over composites (done 2026-09-22)

Blaise v0.12.0 lesson applied: thin-on-features, fuzz the bounds/copies/traps/narrowing paths across the suite before step 4 calls. Suite 68/68 (32 run — incl. 4 trap-aborts — + 36 reject). No new syntax, no new lowering.

Real bug found and fixed

• BoundPair outer IF missing END (M2.atg): the IF invalid THEN ok := FALSE ELSE ... inner IF ... END; action never closed the outer IF. gm2 only warned (syntax warning, «END» missing) and still built, so every green tag since 3.1 carried it. Fixed with one END; build is now warning-free (apart from the known-benign Coco TypeBlock LL(1) advisory). Lesson: treat gm2 warnings as errors from here on — add a grep -i warning gate before step 4.

New coverage (4 tests, all previously unexercised paths)

• t_charbounds → 3: ARRAY ['a'..'c'] bounds + CHAR variable indexing (BoundPair char path, char index checks).
• t_bad_varbound → 230: non-foldable ARRAY [lo..hi] bounds (ConstInt-fail path).
• t_bad_manydims → 230: 9 dimensions (BoundAdd 8-limit, pins the bound as specified behavior).
• t_trap_emptystr → abort: s := "" into a 3-char array (pins the equal-count rule for strings — no silent truncation, consistent with t_trap_count).

Verified already-covered (no duplicates added)

Set narrowing trap (t_trap_setspan), static 222s, deep-copy independence, WITH stacking, cross-span copies, opaque pointers — all present; audit confirmed no gaps there.

Incidental

• Removed stray compiler/src/essai + essai.mod (scratch experiment + linked binary, untracked). Note for its author: the snippet fails only on the trailing ; before END (strict Wirth StatSeq, no trailing separator — same rule as step 1); otherwise the two string assigns are fine.
• Regenerated src/M2.lst committed with the fix.

Deferred (unchanged): enum lowering, HIGH/LEN, recursive DISPOSE, nil-deref trap, class lowering. Next: step 4 calls.