fix reactivity when binding to each context (#4878)

CHANGELOG.md

@@ -10,6 +10,7 @@
 * Add `muted` binding for media elements ([#2998](https://github.com/sveltejs/svelte/issues/2998))
 * Fix let-less `<slot>` with context overflow ([#4624](https://github.com/sveltejs/svelte/issues/4624))
 * Fix `use:` actions being recreated when a keyed `{#each}` is reordered ([#4693](https://github.com/sveltejs/svelte/issues/4693))
+* Fix reactivity when binding directly to `{#each}` context ([#4879](https://github.com/sveltejs/svelte/issues/4879))
 
 ## 3.22.3
 

src/compiler/compile/nodes/Binding.ts

@@ -60,7 +60,7 @@ export default class Binding extends Node {
 			scope.dependencies_for_name.get(name).forEach(name => {
 				const variable = component.var_lookup.get(name);
 				if (variable) {
-					variable[this.expression.node.type === 'MemberExpression' ? 'mutated' : 'reassigned'] = true;
+					variable.mutated = true;
 				}
 			});
 		} else {

test/runtime/samples/reactive-function-called-reassigned/_config.js

@@ -0,0 +1,27 @@
+let value;
+let called = 0;
+function callback(_value) {
+	called ++;
+	value = _value;
+}
+
+export default {
+	props: {
+		callback,
+	},
+	async test({ assert, component, target, window }) {
+		assert.equal(called, 1);
+
+		const input = target.querySelector('input');
+
+		const event = new window.Event('input');
+		input.value = 'h';
+		await input.dispatchEvent(event);
+
+		assert.equal(called, 2);
+		assert.equal(value.length, 3);
+		assert.equal(value[0], 'h');
+		assert.equal(value[1], '2');
+		assert.equal(value[2], '3');
+	}
+};

test/runtime/samples/reactive-function-called-reassigned/main.svelte

@@ -0,0 +1,10 @@
+<script>
+	const refs = ['1','2','3']
+	export let callback = () => {};
+
+	$: callback(refs);
+</script>
+
+{#each refs as ref}
+	<input bind:value={ref} />
+{/each}