Hojun-Cho
c34abf47b1
Wwstage cgcall now mirrors cstage's typed-AST callee-params lookup for module-qualified mod.fn(...) calls, restoring tagged- union widening on cross-module slice args. Class A runtime miscompile — masked from 995_self_rebuild because wwstage tools don't call bytes.index directly; surfaced by lib/strings landing dragging utf8 + bytes into the wwstage-tool dep chain via strings.byteindex's `bytes.X(toutf8(...), n)` call sites. Pre-fix: wwstage's cgcall (cgenexpr.ww) looked up calleeparams only when callee.kind == N_IDENT. For N_DOT callees (the module-qualified mod.fn() form), calleeparams stayed nil → pushargsrev's widening detection gated on param != nil never fired → wwstage fell through to the N_IDENT-slice fast path pushing only 3 slot words (cap, len, ptr) WITHOUT the variant tag. Receiving fn's `match (needle)` then dispatched on (needle.ptr in CX) instead of needle.tag, with R8/R9 carrying .len/.cap instead of .ptr/.len. Wrong arm + wrong payload. Cstage handles N_DOT natively via the checker-set type on n->lhs->type (cmd/w6c/cgen.c:4156-4165), so cg_widen_tagged_push slice path pushes 4 words including tag. Polarity catalog: wwstage UNDER — calleeparams lookup missing N_DOT dispatch arm. Sister to #19 (N_TSLICE variantindex arm), #21 (N_CALL pushargsrev arm), #24 (N_CALL nodeisslice arm), #27 (aliaslookup same-mod-first). The pattern: wwstage dispatchers keep missing arms cstage has natively via typed-AST resolution. Convergence wwstage → cstage (rule 10's spirit overrides letter when correctness is at stake — Path 2 of aligning cstage DOWN would create a runtime miscompile in both stages). Fix: cgcall N_DOT branch pulls module from callee.lhs.str and function name from callee.str, calls new fnparamslookupmod helper. Helper does same-module-first walk then existing first-match fallback (mirrors #27's aliaslookup fix shape). New fnret.fmod field carries module identity; collectfnrets sets f.fmod = d.module at registration. Module-qualified pkg.fn path unchanged. Tests: - 727_modcall_widen_slice pins MOVQ $1 + PUSHQ AX (tag-synth) before the receiving fn's CALL on canonical mod.fn(slice, ...) shape with the callee param widened to a tagged union. Three assertions per row: cstage tag-synth presence, wwstage tag-synth presence, cstage↔wwstage cmp -s byte-id. Sentinel- flip-verified: comment out fnparamslookupmod call → wwstage tag-synth absent + cmp diverges. 99/99 ok. 995_self_rebuild stays green (ww2==ww3==ww4 byte-id).