resubscribe props if reassigned

src/compiler/compile/Component.ts

@@ -772,7 +772,7 @@ export default class Component {
 	invalidate(name, value?) {
 		const variable = this.var_lookup.get(name);
 
-		if (variable && (variable.subscribable && variable.reassigned)) {
+		if (variable && (variable.subscribable && (variable.reassigned || variable.export_name))) {
 			return x`${`$$subscribe_${name}`}($$invalidate('${name}', ${value || name}))`;
 		}
 

src/compiler/compile/render_dom/index.ts

@@ -221,16 +221,18 @@ export default function dom(
 			}
 		});
 
-		component.rewrite_props(({ name, reassigned }) => {
+		component.rewrite_props(({ name, reassigned, export_name }) => {
 			const value = `$${name}`;
+			
+			let insert: string;
+			if (reassigned || export_name) {
+				insert = b`${`$$subscribe_${name}`}()`;
+			} else {
+				const callback = x`$$value => $$invalidate('${value}', ${value} = $$value)`;
 
-			if (reassigned) {
-				return b`${`$$subscribe_${name}`}()`;
+				insert = b`@component_subscribe($$self, ${name}, $${callback})`;
 			}
 
-			const callback = x`$$value => $$invalidate('${value}', ${value} = $$value)`;
-
-			let insert = b`@component_subscribe($$self, ${name}, $${callback})`;
 			if (component.compile_options.dev) {
 				insert = b`@validate_store(${name}, '${name}'); ${insert}`;
 			}
@@ -311,7 +313,7 @@ export default function dom(
 	const resubscribable_reactive_store_unsubscribers = reactive_stores
 		.filter(store => {
 			const variable = component.var_lookup.get(store.name.slice(1));
-			return variable && variable.reassigned;
+			return variable && (variable.reassigned || variable.export_name);
 		})
 		.map(({ name }) => b`$$self.$$.on_destroy.push(() => ${`$$unsubscribe_${name.slice(1)}`}());`);
 
@@ -353,7 +355,7 @@ export default function dom(
 			const name = $name.slice(1);
 
 			const store = component.var_lookup.get(name);
-			if (store && store.reassigned) {
+			if (store && (store.reassigned || store.export_name)) {
 				const unsubscribe = `$$unsubscribe_${name}`;
 				const subscribe = `$$subscribe_${name}`;
 				return b`let ${$name}, ${unsubscribe} = @noop, ${subscribe} = () => (${unsubscribe}(), ${unsubscribe} = @subscribe(${name}, $$value => $$invalidate('${$name}', ${$name} = $$value)), ${name})`;

test/runtime/samples/store-resubscribe-export/_config.js

@@ -0,0 +1,27 @@
+let subscribeCalled = false;
+
+const fakeStore = val => ({
+	subscribe: cb => {
+		cb(val);
+		return {
+			unsubscribe: () => {
+				subscribeCalled = true;
+			},
+		};
+	},
+});
+
+export default {
+	props: {
+		foo: fakeStore(1),
+	},
+	html: `
+		<h1>1</h1>
+	`,
+
+	async test({ assert, component, target }) {
+		component.foo = fakeStore(5);
+
+		return assert.htmlEqual(target.innerHTML, `<h1>5</h1>`);
+	},
+};

test/runtime/samples/store-resubscribe-export/main.svelte

@@ -0,0 +1,6 @@
+<script>
+	import { writable } from 'svelte/store';
+	export let foo = writable(0);
+</script>
+
+<h1>{$foo}</h1>