append/insert of a struct-LITERAL value evaluated the literal's field
exprs AFTER the grow, so a field reading the destination (e.g. len(xs))
saw the grown length. Both stages, #263 gate-blind (cs==ww byte-identical,
both wrong — runtime is the only net). #50 fixed the scalar/boxing value
arm; the struct-lit arm still post-grew.
Fix (mirror #50, both stages): resolve the struct, fill the literal into a
fresh per-site scratch (@appendstructscr, sized esz, survives rt_ensure +
nested-append clobber) BEFORE the grow, then copy scratch -> post-grow slot.
The copy uses the precise descending 8/4/2/1 ladder (the proven N_IDENT
struct arm directly below), NOT a raw 8B-word block copy: a struct's size
rounds to maxalign (check.c:916), so a sub-8B struct packs at a 4/2/1B
slice stride and an 8B copy over-writes past the slot — at a power-of-2
capacity boundary that clobbers the adjacent allocation (heap corruption,
both stages). The ladder never reads past esz (no uninit high bytes) nor
writes past the slot; esz=8 stays a single MOVQ (byte-id preserved).
insert() rides by construction: both stages desugar it to append and
re-dispatch into this arm. The #49 aplace path already uses the precise
ladder (verified, not exposed). #59 closes the last composite-value
eval-order hole in append/insert.
Pin: 946_append_structlit_evalorder_run — append / insert / narrow-neighbor
(i32-field at the cap boundary with an adjacent-allocation survival assert)
rows, each base-fail at 39432f7 and post-pass with cs==ww byte-id.
Hojun-Cho
2c09d13ca3