io.empty (discard+EOF stream, ref/hare/io/empty.ha:4-17) — needed by getopt's
two-pass printusage width measurement. Diverges from Hare's `const empty: *stream`:
a `let _empty_vt` + `fn empty()` that wires the fn-ptr slots per call, because
const-init of a vtable struct with fn-ptr fields is blocked (#118, ruled accept).
Co-discovered while making empty() byte-identical across stages: three
wwstage-only cgen fixes (cstage was already correct; wwstage aligned down):
- #129 sretretsize: consult the same-module pointer-alias before structlookup's
any-module struct fallback (io.stream = *vtable was mis-sized as memio's 56B
struct -> spurious sret save).
- #129 callsretsize: swap curmod to the callee's module before sret-size
classification (cross-module callee context).
- #130 cgassign global-struct tagged-union field store: add the missing arm
(was a 1-word store) mirroring cstage cgen.c:4893-4912.
The three are inseparable from io.empty here — splitting them out leaves a
divergent-asm intermediate (993/995 red), so they ride one commit per the
one-class gate-repair carve-out (#133-expanded precedent). Regenerates the
embedded combined.ww; 989_lib_byteid pins bufio + fmt graduated to M_ID.
(cgenexpr.ww fix-3 inline comment cites the #129 cluster; narrow to #130 on
next touch to avoid a regen for a comment.)
Hojun-Cho
f3750ae3ce