cmd/wcc/check.c silently accepted `let a; let a;` in the same block
and similar redecls. Pre-#27 the localoff dedup masked it; post-#27
last-write-wins via head-first localfind. Surfaced by worker-27
during the #27 review.
Cstage: 5 guard sites (check_scope_define-NULL → err) covering
N_LET block-bind, N_MLET tuple binders (incl. same-tuple
`let (a,a)`), N_FORRANGE tuple binders, top-level let, fn param.
Voice: "<kind> '<name>' redeclared in same scope" for inner;
"duplicate let %s" for top-let, matching the existing
"duplicate <kind>" idiom at 1812/1851/1872.
Wwstage: TODO(#11) comments at the 4 mirror sites (installdecl,
N_FORRANGE, N_LET, installparams). Full enforcement waits on the
checkfile pass per rob.
**Unmasked by #32 (worth flagging):** selfhost/cmd/wcc/cgenexpr.ww
cgcall had `let callee: *node = n.lhs;` twice at fn-body scope
(copy-paste, identical value). Pre-fix silent-redecl absorbed it;
post-fix the new guard rejects. Removed the second decl — outer
`callee` stays visible across the intermediate block.
Test 712 (redecl): 10 rows (6 neg + 4 pos), cstage-only per rob.
Negative rows cover all 5 guard sites + same-tuple-dup. Positive
rows pin the legal counter-shapes (cross-block, name-only bucket,
forrange body, mcase-per-arm).
Test 300 row 34 ("shadowing in inner scope; same scope flagged")
was incorrectly asserting the bug; flipped to expect "redeclared"
and added a sibling row pinning cross-block shadow stays ok. Test
709's `same_block_redecl_pin` canary (explicitly documented as
flipping under #32) removed; pointer to 712 left in its place.
localoff (cstage) / localadd (wwstage) deduped stack slots by name
alone, ignoring scope. Outer `let a: [128]u8` and an inner-block
`let a: *u8` shared one 8B slot; prologue truncated to inner size
and outer-scope writes past saved RIP corrupted the frame. Worker-19
hit it during #19 (selfhost/cmd/w6a/main.ww carries a defensive
asm→s rename pointing at this task).
Drop the name-dedup. Each let allocates fresh. Then preserve
outer-scope visibility across inner blocks: cgstmt's N_BLOCK case
saves `*locals` head, walks body, restores. cgfn iterates fn->body
->list directly (bypassing the outermost N_BLOCK) so defers and the
implicit-return epilogue still see fn-body locals after the loop.
Wwstage symmetric: localadd keeps dedup only for `@`-prefixed
synthetic scratches (`@tagscr` / `@retscr` / `@tagbase`) which need
single-slot semantics; user names get fresh stubs. scanlocals always
counts + always appends a fresh stub for N_LET / N_MLET / N_FORRANGE
so prologue SUBQ stays in sync with emit-time offsets. cgblock and
cgfn mirror cstage.
ww2 == ww3 == ww4 byte-identical post-fix.
Test 709 (localoff_scope): 8 rows × 2 drivers = 16 fixtures —
inner_first_outer_bigger, outer_first_inner_writes, nested_3_deep,
same_name_diff_type, same_block_redecl_pin, defer_shadow,
forrange_body_shadow, if_body_shadow. defer_shadow pins the cgfn
body-bypass; if_body_shadow pins the save/restore independently.
Asm byte-id not diffed in 709 — 995_self_rebuild covers cross-stage
drift more broadly.
Follow-ups (filed): #32 (check: refuse same-block let-redecl), w6a
`s`→`asm` revert sibling commit.
