syntax+w6c: multi-type match patterns in wwstage (align up to cstage)

`case T1 | T2 =>` (binding-less; cstage parse.c:635-650 chains extra
types through cs->list, bindings stay single-type by design). Three
wwstage layers, no AST change (node.list already exists):
- parser (expr.ww): pipe loop after the non-let arm's first
  parsetype;
- checker (check.ww): resolvewalk N_MCASE now walks n.list so each
  alt gets its type_ stamp (exhaustiveness/casecovers were already
  alt-aware, built ahead of the parser);
- cgen (cgenexpr.ww): the single-pattern want-computation moves
  VERBATIM into matcharmwant; a cs.list arm emits CMPQ/JE per alt
  funneling into one match_body label, mirroring cgen.c:11118-11141
  incl. label mint order and the tag<0 clamp. Nullable arms keep
  ignoring alts (both stages).

Graduates the held e2e row (pin 1732/1158/3464); byte-identical on
the repro and the single-pattern control.

internal/wwfixture/types.ww

@@ -1,13 +1,13 @@
 package wwfixture;
 
 def protocolversion: i32 = 1;
-def corpuscount: i32 = 1731;
+def corpuscount: i32 = 1732;
 def errorcount: i32 = 343;
 def compilecount: i32 = 22;
 def runcount: i32 = 209;
-def runexitcount: i32 = 1157;
-def nativecount: i32 = 3462;
-def corpushash: str = "6786916caba20c07c47eaaa0507dd2707fd162b708904b6e72187afb02233bf9";
+def runexitcount: i32 = 1158;
+def nativecount: i32 = 3464;
+def corpushash: str = "df3862c647aae744b549089ab4a180b36371fe898f5996c13099f52da203265e";
 
 type directive = enum i32 {
 	ERROR = 0,

lib/ww/syntax/expr.ww

@@ -205,6 +205,17 @@ fn parseprimary(p: *parser) *node = {
 				mc.lhs = parsetype(p);
 			} else { if (p.curkind != tkind.TK_FATARROW) {
 				mc.lhs = parsetype(p);
+				// `case T1 | T2 | ... =>`: extra types chain
+				// through mc.list. Binding arms stay single-type
+				// (a binding over a multi-pattern would need the
+				// union type) — mirrors cmd/wcc/parse.c:643.
+				let alttail: *node = nil;
+				for (accepttok(p, tkind.TK_PIPE)) {
+					let more: *node = parsetype(p);
+					if (mc.list == nil) { mc.list = more; }
+					else { alttail.next = more; };
+					alttail = more;
+				};
 			};};
 			expecttok(p, tkind.TK_FATARROW, "expected '=>' in match arm");
 			mc.body = parsestmt(p);

selfhost/cmd/wcc/cgenexpr.ww

@@ -3090,6 +3090,41 @@ fn cgslice(c: *cgen, n: *syntax.node) void = {
 	};
 };
 
+// matcharmwant — variant tag a non-nullable match pattern selects on
+// the scrutinee's tagged union; 0 when unresolvable (cstage's tag<0
+// clamp, cmd/w6c/cgen.c:11124). Serves the single-pattern arm and each
+// `case T1 | T2` alt identically.
+fn matcharmwant(c: *cgen, scrutt: *syntax.node, pat: *syntax.node) i32 = {
+	let want: i32 = 0;
+	if (scrutt != nil) {
+		// #67: gate on the stamped tinfo, not the node kind
+		// — matchscrutt now returns the scrutinee node itself
+		// for an N_DOT field (its .type_ is the tagged tinfo)
+		// rather than the resolved N_TTAGGED node.
+		if (istaggedtype(c, scrutt)) {
+			let r: i32 = -1;
+			let pattype: *syntax.tinfo = pat.type_: *syntax.tinfo;
+			if (pattype != nil) {
+				// #179: kind-agnostic dispatch on the resolved
+				// tinfo. Cstage cg_tag_for_variant works on
+				// Type, so N_TPTR / N_TFN / N_TPTR(N_TFN) case-
+				// patterns all reach typeeq; the prior pat.kind
+				// gate dropped them to r=-1 → tag 0 collapse.
+				// Slice arm still goes through flatslicevariantidx
+				// (task #19 untyped-elem fallback when typeeq
+				// can't match a (scalar | []T) shape).
+				if (syntax.typeisslice(pattype)) {
+					r = flatslicevariantidx(c, scrutt, pat.lhs);
+				} else {
+					r = flatvariantidxt(scrutt.type_: *syntax.tinfo, pattype, false);
+				};
+			};
+			if (r >= 0) { want = r; };
+		};
+	};
+	return want;
+};
+
 fn cgmatch(c: *cgen, n: *syntax.node) void = {
 	// match (e) { case let v: T => stmt; ... }
 	//
@@ -3326,42 +3361,44 @@ fn cgmatch(c: *cgen, n: *syntax.node) void = {
 				emitline(nxt);
 				emitline("\n");
 			} else {
-				let want: i32 = 0;
-				if (scrutt != nil) {
-					// #67: gate on the stamped tinfo, not the node kind
-					// — matchscrutt now returns the scrutinee node itself
-					// for an N_DOT field (its .type_ is the tagged tinfo)
-					// rather than the resolved N_TTAGGED node.
-					if (istaggedtype(c, scrutt)) {
-						let r: i32 = -1;
-						let pattype: *syntax.tinfo = pat.type_: *syntax.tinfo;
-						if (pattype != nil) {
-							// #179: kind-agnostic dispatch on the resolved
-							// tinfo. Cstage cg_tag_for_variant works on
-							// Type, so N_TPTR / N_TFN / N_TPTR(N_TFN) case-
-							// patterns all reach typeeq; the prior pat.kind
-							// gate dropped them to r=-1 → tag 0 collapse.
-							// Slice arm still goes through flatslicevariantidx
-							// (task #19 untyped-elem fallback when typeeq
-							// can't match a (scalar | []T) shape).
-							if (syntax.typeisslice(pattype)) {
-								r = flatslicevariantidx(c, scrutt, pat.lhs);
-							} else {
-								r = flatvariantidxt(scrutt.type_: *syntax.tinfo, pattype, false);
-							};
-						};
-						if (r >= 0) { want = r; };
-					};
-				};
+				let want: i32 = matcharmwant(c, scrutt, pat);
 				emitline("\tMOVQ\t");
 				emitoff(scrutoff: i64);
 				emitline("(BP), AX\n");
-				emitline("\tCMPQ\t$");
-				emitint(want: i64);
-				emitline(", AX\n");
-				emitline("\tJNE\t");
-				emitline(nxt);
-				emitline("\n");
+				if (cs.list != nil) {
+					// Multi-pattern `case T1 | T2 =>`: any
+					// matching alt funnels into one body
+					// label. Mirrors cmd/w6c/cgen.c:11118.
+					let bodyl: str = mklabel(c, "match_body");
+					emitline("\tCMPQ\t$");
+					emitint(want: i64);
+					emitline(", AX\n");
+					emitline("\tJE\t");
+					emitline(bodyl);
+					emitline("\n");
+					let alt: *syntax.node = cs.list;
+					for (alt != nil) {
+						let awant: i32 = matcharmwant(c, scrutt, alt);
+						emitline("\tCMPQ\t$");
+						emitint(awant: i64);
+						emitline(", AX\n");
+						emitline("\tJE\t");
+						emitline(bodyl);
+						emitline("\n");
+						alt = alt.next;
+					};
+					emitline("\tJMP\t");
+					emitline(nxt);
+					emitline("\n");
+					emitlabel(bodyl);
+				} else {
+					emitline("\tCMPQ\t$");
+					emitint(want: i64);
+					emitline(", AX\n");
+					emitline("\tJNE\t");
+					emitline(nxt);
+					emitline("\n");
+				};
 			};
 		};
 		// Bind `let v: T` from the slot, if requested.

selfhost/cmd/wcc/check.ww

@@ -671,6 +671,14 @@ fn resolvewalk(c: *checker, n: *syntax.node) void = {
 	// Mirrors cmd/wcc/check.c's newscope/saved-restore around cstmt.
 	if (k == syntax.nkind.N_MCASE) {
 		if (n.lhs  != nil) { resolvewalk(c, n.lhs);  };
+		// `case T1 | T2` alts ride n.list; each needs its type_
+		// stamp or cgmatch's tag lookup collapses to 0. Mirrors
+		// cmd/wcc/check.c:2140 (per-alt resolve).
+		let alt: *syntax.node = n.list;
+		for (alt != nil) {
+			resolvewalk(c, alt);
+			alt = alt.next;
+		};
 		let outer: *syntax.scope = c.cur;
 		c.cur = syntax.newscope(outer);
 		let nm: str = n.str;

test/wcc/data/r700_match_multi_pattern/case.ww

@@ -0,0 +1,27 @@
+//ww:run-exit 18
+// Migrated from 700_e2e row 72.
+package main;
+fn pick(n: i64) (i64 | i32 | u32) = {
+  if (n < 0) { return 1: i32; };
+  if (n == 0) { return 2: u32; };
+  return n;
+};
+fn main() i32 = {
+  let r1: (i64 | i32 | u32) = pick(0);
+  let r2: (i64 | i32 | u32) = pick(-1);
+  let r3: (i64 | i32 | u32) = pick(7);
+  let acc: i32 = 0;
+  match (r1) {
+    case let v: i64 => acc += 100;
+    case i32 | u32 => acc += 1;
+  };
+  match (r2) {
+    case let v: i64 => acc += 100;
+    case i32 | u32 => acc += 10;
+  };
+  match (r3) {
+    case let v: i64 => acc += v: i32;
+    case i32 | u32 => acc += 100;
+  };
+  return acc;
+};