ww package: reject non-function main declarations

selfhost/cmd/wcc/check.ww

@@ -7696,6 +7696,36 @@ fn classifyinitdecls(c: *checker, file: *syntax.node) void = {
 	};
 };
 
+// Pinned Go 1.26.5 types2 rejects a non-function package-scope `main`
+// before declaring it, but only when the declared package name is `main`
+// (resolver.go:90-110 declarePkgObj). WW's function entry ABI deliberately
+// permits argument/result-bearing functions, so this is the independent
+// declaration-kind rule: canonical identity, physical directory, path leaf,
+// and root/action status are not inputs. Remove rejected declarations from
+// later name installation just as the pinned resolver returns without
+// declaring its object. Twin of cmd/wcc/check.c.
+fn rejectnonfunctionmaindecls(c: *checker, file: *syntax.node) void = {
+	let prev: *syntax.node = nil;
+	let d: *syntax.node = file.list;
+	for (d != nil) {
+		let next: *syntax.node = d.next;
+		let invalid: bool = topdeclkind(d)
+			&& d.kind != syntax.nkind.N_FNDECL
+			&& syntax.streq(d.str, "main")
+			&& syntax.streq(d.pkgname, "main");
+		if (invalid) {
+			importdiagprefix(d);
+			cerr("cannot declare main - must be func\n");
+			c.errs += 1;
+			if (prev == nil) { file.list = next; }
+			else { prev.next = next; };
+		} else {
+			prev = d;
+		};
+		d = next;
+	};
+};
+
 fn initstripcast(n: *syntax.node) *syntax.node = {
 	for (n != nil && n.kind == syntax.nkind.N_CAST) { n = n.lhs; };
 	return n;
@@ -8578,6 +8608,7 @@ fn checkfile(c: *checker, file: *syntax.node) void = {
 			file.list = usenode;
 		};
 		};
+	rejectnonfunctionmaindecls(c, file);
 	markimportuses(c, file);
 	checkimportredeclarations(c, file);
 	checkimportusageandcollisions(c, file);