update stores when assigning to store values - fixes #2170

src/compile/Component.ts

@@ -719,9 +719,15 @@ export default class Component {
 
 	invalidate(name, value = name) {
 		const variable = this.var_lookup.get(name);
+
 		if (variable && (variable.subscribable && variable.reassigned)) {
 			return `$$subscribe_${name}(), $$invalidate('${name}', ${value})`;
 		}
+
+		if (name[0] === '$' && name[1] !== '$') {
+			return `${name.slice(1)}.set(${name})`
+		}
+
 		return `$$invalidate('${name}', ${value})`;
 	}
 

test/runtime/samples/store-assignment-updates/_config.js

@@ -0,0 +1,32 @@
+import { writable } from '../../../../store.js';
+
+export default {
+	show: 1,
+	props: {
+		count: writable(0)
+	},
+
+	html: `
+		<button>count 0</button>
+		<p>doubled: 0</p>
+	`,
+
+	async test({ assert, component, target, window }) {
+		const button = target.querySelector('button');
+		const click = new window.MouseEvent('click');
+
+		await button.dispatchEvent(click);
+
+		assert.htmlEqual(target.innerHTML, `
+			<button>count 1</button>
+			<p>doubled: 2</p>
+		`);
+
+		await component.count.set(42);
+
+		assert.htmlEqual(target.innerHTML, `
+			<button>count 42</button>
+			<p>doubled: 84</p>
+		`);
+	}
+};

test/runtime/samples/store-assignment-updates/main.svelte

@@ -0,0 +1,10 @@
+<script>
+	import { derive } from 'svelte/store';
+
+	export let count;
+
+	const doubled = derive(count, $count => $count * 2);
+</script>
+
+<button on:click="{() => $count += 1}">count {$count}</button>
+<p>doubled: {$doubled}</p>