compiler: tag auto-subscribe stores as referenced in vars (#4089)

src/compiler/compile/Component.ts

@@ -203,7 +203,10 @@ export default class Component {
 			const subscribable_name = name.slice(1);
 
 			const variable = this.var_lookup.get(subscribable_name);
-			if (variable) variable.subscribable = true;
+			if (variable) {
+				variable.referenced   = true;
+				variable.subscribable = true;
+			}
 		} else {
 			this.used_names.add(name);
 		}

test/js/samples/component-store-access-invalidate/expected.js

@@ -43,7 +43,7 @@ function instance($$self, $$props, $$invalidate) {
 	let $foo;
 	const foo = writable(0);
 	component_subscribe($$self, foo, value => $$invalidate(0, $foo = value));
-	return [$foo];
+	return [$foo, foo];
 }
 
 class Component extends SvelteComponent {

test/vars/samples/store-referenced/_config.js

@@ -8,7 +8,7 @@ export default {
 				module: false,
 				mutated: false,
 				reassigned: false,
-				referenced: false,
+				referenced: true,
 				referenced_from_script: false,
 				writable: true
 			},