The wwstage checker rejected a match-bound binder used in a `yield` arm
of a match-AS-EXPRESSION (`let v = match (x) { case let p: *T => yield
*p; ... }`) with asserttyped:un/bin/index; cstage compiled it.
resolvewalk stamps the yield operand's type_ during the in-scope N_MCASE
arm walk. exprtype's N_MATCH arm then derived the match's type by
re-running exprtype on the same operand to recover a type NODE — but the
arm binder's scope is already popped, so the re-derive returned nil and
the N_UN/N_BIN/N_INDEX restamp arms overwrote the good in-scope stamp
with nil. cstage never re-runs: match_yield_type reads the operand's
cached ->type (cmd/wcc/check.c:121).
Root fix (align wwstage UP): matchyieldtype now returns a *tinfo and, at
the post-walk call, READS the operand's cached node.type_ instead of
re-running exprtype — so no operand shape can be clobbered by
construction (deref/bin/index all vanish, no per-arm guards). The
exprtype N_MATCH consumer stamps e.type_ from that tinfo directly (no
tinfofornode round-trip). The pre-walk call (checkletassign L302 /
checkretassign L303 run before the in-scope arm walk, so the operand is
nil there) keeps the nil-safe re-derive — benign and load-bearing: it
types the void-arm literal so let/return-assign has a usable node. The
re-derived node (or btype for the bare-binder idiom) is carried back via
an out-param for the assignability check and for the N_MLET/N_MASSIGN
tuple-destructure consumers (`let (a,b) = match { case let t => yield t
}`, test 945). cstage is single-pass so its else is dead; eliminating
the pre-walk call is #279.
Supersedes the narrow N_UN non-clobber guard (removed — its match
consumer is gone). @test check_match_ptr_deref extended to pin the whole
operand class (deref / bin / slice-index / deref-then-field), dual-stage
(910 + 997) with correct runtime + cs==ww byte-id. The *[N]T ptr-to-
array index variant is blocked separately by #278. Both compiler-
imported combined.ww regenerated. smoke + test-unit (242) + 994 w6c_ww
byte-id (18 corpus incl. selfhost combined.ww) green.
Hojun-Cho
bec1e7d6b0