isassignable's tagged-variant inclusion was resolvealias-unwrapping
both src and each variant before typeeqast. Two NAMED structs (e.g.
`(void | err)` with src=`err`) both flattened to N_TSTRUCT and
typeeqast's conservative struct branch returned false — false
positive on the assignability.
Cstage variant_match (cmd/wcc/check.c:90-100) compares TY_NAMED
pointer-identically, so the nominal name short-circuits before any
body inspection. Mirror: try typeeqast on unwrapbang'd src vs
unwrapbang'd variant first (catches the N_TNAME nominal match),
fall through to resolvealias + structural compare for anonymous-
union variants only.
Reviewer's negative probe (different types modA.err vs modB.err
with same leaf name) still correctly rejects — the parser joins
pkg.alias into one TNAME string, so modA.err ≠ modB.err at the
nominal level.
Bare-vs-qualified residual (cstage admits `(void | M.err)` ← bare
`err` inside module M; wwstage still rejects) tracked as #57. Not
hit by any current fixture; unblocks #50 (after #56) and #42.
131/131 + 4 lines of pre-existing pessimism cleared in
selfhost/cmd/wcc/check.ww's own resolution.
Hojun-Cho
9fed4ca492