wcc/ww: reject value-less return in a non-void fn (catB-24)

wwstage's checkretassign short-circuited on a value-less `return;`
("skip flagging for now"), so `fn f() i32 = { return; }` built and
RET'd a garbage register. Mirror cstage cmd/wcc/check.c:2428-2439:
the no-value return has type void, then run isassignable(c.fnret,
void) — void→void and void→(T|void) accept, void→i32 is a confident
reject. cstage already rejected; this aligns wwstage's w6c_ww UP.

Regen w6c/wwdump combined.ww (checker embeds in both). Valid-program
codegen unchanged → cs==ww byte-id gate stays green.

Makefile

@@ -248,6 +248,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_arr_tagged_elem \
 	  $(BIN)/test_dup_main_reject \
 	  $(BIN)/test_tuple_trailing_comma_reject \
+	  $(BIN)/test_voidless_return_reject \
 	  $(BIN)/test_size_untyped_int \
 	  $(BIN)/test_tagged_staticinit \
 	  $(BIN)/test_arr_infer_len \
@@ -1456,6 +1457,12 @@ $(BIN)/test_tuple_trailing_comma_reject: test/wcc/845_tuple_trailing_comma_rejec
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_voidless_return_reject: test/wcc/846_voidless_return_reject.c $(BIN)/ww \
+		$(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
+		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_tagged_staticinit: test/wcc/843_tagged_staticinit.c $(BIN)/ww \
 		$(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \

selfhost/cmd/w6c/main.combined.ww

@@ -16253,9 +16253,18 @@ fn checkletassign(c: *checker, n: *node) void = {
 fn checkretassign(c: *checker, n: *node) void = {
 	if (n == nil) { return; };
 	if (n.lhs == nil) {
-		// bare `return;` — OK iff fnret is void or a tagged union
+		// bare `return;` — mirror cstage cmd/wcc/check.c:2428-2439:
-		// with a void variant. Skip flagging for now; cgen handles
+		// the value-less return has type void, then type_assignable
-		// the void-variant tag synthesis already.
+		// (c.fnret, void). A void fnret or a tagged union carrying a
+		// void variant accepts; a non-void scalar fnret rejects (the
+		// value-less return would RET a garbage register). isassignable
+		// reaches the same verdict (void→void typeeqast; void→tagged via
+		// the void variant; void→i32 a confident primitive mismatch).
+		if (c.fnret == nil) { return; };
+		let vt: *node = mktname(c, "void");
+		let vconf: bool = false;
+		let vok: bool = isassignable(c, c.fnret, vt, &vconf);
+		if (vconf) { if (!vok) { errnotassign(c, c.fnret, vt, "return"); }; };
 		return;
 	};
 	if (c.fnret == nil) { return; };

selfhost/cmd/wcc/check.ww

@@ -5779,9 +5779,18 @@ fn checkletassign(c: *checker, n: *node) void = {
 fn checkretassign(c: *checker, n: *node) void = {
 	if (n == nil) { return; };
 	if (n.lhs == nil) {
-		// bare `return;` — OK iff fnret is void or a tagged union
+		// bare `return;` — mirror cstage cmd/wcc/check.c:2428-2439:
-		// with a void variant. Skip flagging for now; cgen handles
+		// the value-less return has type void, then type_assignable
-		// the void-variant tag synthesis already.
+		// (c.fnret, void). A void fnret or a tagged union carrying a
+		// void variant accepts; a non-void scalar fnret rejects (the
+		// value-less return would RET a garbage register). isassignable
+		// reaches the same verdict (void→void typeeqast; void→tagged via
+		// the void variant; void→i32 a confident primitive mismatch).
+		if (c.fnret == nil) { return; };
+		let vt: *node = mktname(c, "void");
+		let vconf: bool = false;
+		let vok: bool = isassignable(c, c.fnret, vt, &vconf);
+		if (vconf) { if (!vok) { errnotassign(c, c.fnret, vt, "return"); }; };
 		return;
 	};
 	if (c.fnret == nil) { return; };

selfhost/cmd/wwdump/main.combined.ww

@@ -16253,9 +16253,18 @@ fn checkletassign(c: *checker, n: *node) void = {
 fn checkretassign(c: *checker, n: *node) void = {
 	if (n == nil) { return; };
 	if (n.lhs == nil) {
-		// bare `return;` — OK iff fnret is void or a tagged union
+		// bare `return;` — mirror cstage cmd/wcc/check.c:2428-2439:
-		// with a void variant. Skip flagging for now; cgen handles
+		// the value-less return has type void, then type_assignable
-		// the void-variant tag synthesis already.
+		// (c.fnret, void). A void fnret or a tagged union carrying a
+		// void variant accepts; a non-void scalar fnret rejects (the
+		// value-less return would RET a garbage register). isassignable
+		// reaches the same verdict (void→void typeeqast; void→tagged via
+		// the void variant; void→i32 a confident primitive mismatch).
+		if (c.fnret == nil) { return; };
+		let vt: *node = mktname(c, "void");
+		let vconf: bool = false;
+		let vok: bool = isassignable(c, c.fnret, vt, &vconf);
+		if (vconf) { if (!vok) { errnotassign(c, c.fnret, vt, "return"); }; };
 		return;
 	};
 	if (c.fnret == nil) { return; };

test/wcc/846_voidless_return_reject.c

@@ -0,0 +1,185 @@
+/*
+ * 846_voidless_return_reject (catB-24) — cstage and wwstage LOUD-REJECT
+ * a value-less `return;` in a function whose return type is not void.
+ *
+ * `fn f() i32 = { return; }` would RET a garbage value register — a
+ * common programmer slip. cstage rejects at cmd/wcc/check.c:2428-2439
+ * (a value-less return has type void, then type_assignable(c->ret,
+ * void) fails for a non-void scalar). wwstage's checkretassign
+ * short-circuited on the no-value case ("skip flagging for now"), a
+ * silent accept. The fix builds a void source type and runs the same
+ * isassignable verdict: void→void and void→(T|void) accept, void→i32
+ * is a confident reject.
+ *
+ *   row        | shape                       | expect
+ *   -----------+-----------------------------+--------
+ *   nonvoid    | fn f() i32 = { return; };   | REJECT
+ *   void_ok    | fn f() void = { return; };  | BUILD, run 5
+ *   value_ok   | fn f() i32 = { return 5; }; | BUILD, run 5
+ *   tagged_ok  | fn f() (i32|void) ... return;| BUILD, run 9
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+
+static int
+runwait(const char *cmd)
+{
+	int rc = system(cmd);
+	if (rc == -1) return -1;
+	if (WIFEXITED(rc)) return WEXITSTATUS(rc);
+	return -1;
+}
+
+static void
+outbin(char *dst, size_t n, const char *tmpdir, const char *src)
+{
+	const char *base = strrchr(src, '/');
+	base = base ? base + 1 : src;
+	snprintf(dst, n, "%s/%s", tmpdir, base);
+	char *dot = strrchr(dst, '.');
+	if (dot && strcmp(dot, ".ww") == 0) *dot = '\0';
+}
+
+static int
+build_should_fail(const char *driver, const char *label, const char *src,
+    int i)
+{
+	char s[64], tmpdir[64], cmd[1024], bin[128];
+	snprintf(s, sizeof s, "/tmp/vret_%d_%d.ww", getpid(), i);
+	snprintf(tmpdir, sizeof tmpdir, "/tmp/vret_%d_d_%d", getpid(), i);
+	FILE *f = fopen(s, "wb");
+	if (!f) return -1;
+	fputs(src, f);
+	fclose(f);
+	mkdir(tmpdir, 0755);
+	snprintf(cmd, sizeof cmd, "cd %s && %s build %s 2>/dev/null",
+	    tmpdir, driver, s);
+	int rc = runwait(cmd);
+	outbin(bin, sizeof bin, tmpdir, s);
+	unlink(s);
+	unlink(bin);
+	rmdir(tmpdir);
+	if (rc == 0)
+		fprintf(stderr, "vret[%s][%s]: built ok, expected a reject\n",
+		    driver, label);
+	return rc == 0 ? -1 : 0;
+}
+
+static int
+run_build(const char *driver, const char *label, const char *src, int i)
+{
+	char s[64], tmpdir[64], cmd[1024], bin[128];
+	snprintf(s, sizeof s, "/tmp/vret_ok_%d_%d.ww", getpid(), i);
+	snprintf(tmpdir, sizeof tmpdir, "/tmp/vret_ok_%d_d_%d", getpid(), i);
+	FILE *f = fopen(s, "wb");
+	if (!f) return -1;
+	fputs(src, f);
+	fclose(f);
+	mkdir(tmpdir, 0755);
+	snprintf(cmd, sizeof cmd, "cd %s && %s build %s 2>/dev/null",
+	    tmpdir, driver, s);
+	if (runwait(cmd) != 0) {
+		fprintf(stderr, "vret[%s][%s]: build failed (a valid return "
+		    "must compile)\n", driver, label);
+		unlink(s); rmdir(tmpdir);
+		return -1;
+	}
+	outbin(bin, sizeof bin, tmpdir, s);
+	int got = runwait(bin);
+	unlink(s); unlink(bin); rmdir(tmpdir);
+	return got;
+}
+
+struct rejrow { const char *label; const char *src; };
+
+static const struct rejrow reject_rows[] = {
+	{ "nonvoid",
+	  "package main;\n"
+	  "fn f() i32 = { return; };\n"
+	  "fn main() i32 = { return f(); };\n" },
+};
+
+struct okrow { const char *label; const char *src; int want; };
+
+static const struct okrow ok_rows[] = {
+	{ "void_ok",
+	  "package main;\n"
+	  "fn f() void = { return; };\n"
+	  "fn main() i32 = { f(); return 5; };\n", 5 },
+
+	{ "value_ok",
+	  "package main;\n"
+	  "fn f() i32 = { return 5; };\n"
+	  "fn main() i32 = { return f(); };\n", 5 },
+
+	{ "tagged_ok",
+	  "package main;\n"
+	  "fn f(x: i32) (i32 | void) = { if (x > 0) { return x; }; return; };\n"
+	  "fn main() i32 = { match (f(0)) { case let v: i32 => return v; "
+	  "case => return 9; }; };\n", 9 },
+};
+
+int
+main(void)
+{
+	const char *bin = getenv("BIN");
+	if (!bin) bin = "out/bin";
+	char absbin[1024];
+	if (bin[0] != '/') {
+		char cwd[1024];
+		if (getcwd(cwd, sizeof cwd) == NULL) return 1;
+		snprintf(absbin, sizeof absbin, "%s/%s", cwd, bin);
+		bin = absbin;
+	}
+
+	char cdrv[1024], wdrv[1024];
+	snprintf(cdrv, sizeof cdrv, "%s/ww", bin);
+	snprintf(wdrv, sizeof wdrv, "%s/ww_ww", bin);
+
+	struct { const char *name; const char *path; int gated; } drivers[] = {
+		{ "cstage",  cdrv, 0 },
+		{ "wwstage", wdrv, 1 },
+		{ NULL, NULL, 0 },
+	};
+
+	int nrej = (int)(sizeof reject_rows / sizeof reject_rows[0]);
+	int nok = (int)(sizeof ok_rows / sizeof ok_rows[0]);
+	int total = 0, fail = 0;
+
+	for (int d = 0; drivers[d].name; d++) {
+		if (drivers[d].gated && access(drivers[d].path, X_OK) != 0) {
+			fprintf(stderr, "vret: skip %s (no %s)\n",
+			    drivers[d].name, drivers[d].path);
+			continue;
+		}
+		for (int i = 0; i < nrej; i++) {
+			total++;
+			if (build_should_fail(drivers[d].path,
+			    reject_rows[i].label, reject_rows[i].src,
+			    d * 100 + i) != 0)
+				fail++;
+		}
+		for (int i = 0; i < nok; i++) {
+			total++;
+			int got = run_build(drivers[d].path, ok_rows[i].label,
+			    ok_rows[i].src, d * 100 + i);
+			if (got != ok_rows[i].want) {
+				fprintf(stderr, "vret[%s][%s]: exit=%d want=%d\n",
+				    drivers[d].name, ok_rows[i].label,
+				    got, ok_rows[i].want);
+				fail++;
+			}
+		}
+	}
+
+	if (fail) {
+		fprintf(stderr, "vret: %d/%d fixtures failed\n", fail, total);
+		return 1;
+	}
+	printf("vret: %d/%d ok\n", total, total);
+	return 0;
+}