[fix] bind:this works during onMount callback in manually-created component

src/runtime/internal/scheduler.ts

@@ -1,7 +1,7 @@
-import { run_all } from './utils';
-import { set_current_component } from './lifecycle';
+import { run_all, Queue } from './utils';
+import { get_current_component, set_current_component } from './lifecycle';
 
-export const dirty_components = [];
+export const dirty_components = new Queue<any>();
 export const intros = { enabled: false };
 
 export const binding_callbacks = [];
@@ -31,17 +31,21 @@ export function add_flush_callback(fn) {
 	flush_callbacks.push(fn);
 }
 
-let flushing = false;
 const seen_callbacks = new Set();
 export function flush() {
-	if (flushing) return;
-	flushing = true;
+
+	let current_component = null;
+	try {
+		current_component = get_current_component();
+	} catch {
+		// no current component, so leave it as null
+	}
 
 	do {
 		// first, call beforeUpdate functions
 		// and update components
-		for (let i = 0; i < dirty_components.length; i += 1) {
-			const component = dirty_components[i];
+		while (dirty_components.length) {
+			const component = dirty_components.shift();
 			set_current_component(component);
 			update(component.$$);
 		}
@@ -68,12 +72,13 @@ export function flush() {
 		render_callbacks.length = 0;
 	} while (dirty_components.length);
 
+	set_current_component(current_component);
+
 	while (flush_callbacks.length) {
 		flush_callbacks.pop()();
 	}
 
 	update_scheduled = false;
-	flushing = false;
 	seen_callbacks.clear();
 }
 

src/runtime/internal/utils.ts

@@ -58,6 +58,40 @@ export function is_empty(obj) {
 	return Object.keys(obj).length === 0;
 }
 
+export class Queue<T> {
+	forward: T[];
+	reverse: T[];
+
+	constructor() {
+		this.forward = [];
+		this.reverse = [];
+	}
+	push(value: T) {
+		return this.forward.push(value);
+	}
+	shift() {
+		if (this.reverse.length === 0) {
+			while (this.forward.length) {
+				this.reverse.push(this.forward.pop());
+			}
+		}
+		return this.reverse.pop();
+	}
+	get length() {
+		return this.forward.length + this.reverse.length;
+	}
+	set length(len: number) {
+		if (len === 0) {
+			this.forward.length = 0;
+			this.reverse.length = 0;
+		} else {
+			while (this.length > len) {
+				this.shift();
+			}
+		}
+	}
+}
+
 export function validate_store(store, name) {
 	if (store != null && typeof store.subscribe !== 'function') {
 		throw new Error(`'${name}' is not a store with a 'subscribe' method`);

test/runtime/samples/component-binding-onMount/Mount.svelte

@@ -0,0 +1,15 @@
+<script>
+	import { onMount } from 'svelte';
+
+	let element;
+	let bound = false;
+	onMount(() => {
+		if (element) bound = true;
+	});
+
+</script>
+
+<div bind:this={element}></div>
+<p>
+	Bound? {bound}
+</p>

test/runtime/samples/component-binding-onMount/_config.js

@@ -0,0 +1,11 @@
+export default {
+	async test({ assert, target }) {
+		assert.htmlEqual(target.innerHTML, `
+		<div id="target"><div></div>
+			<p>
+				Bound? true
+			</p>
+		</div>
+	`);
+	}
+};

test/runtime/samples/component-binding-onMount/main.svelte

@@ -0,0 +1,13 @@
+<script>
+	import Mount from './Mount.svelte';
+	import { onMount } from 'svelte';
+
+	onMount(() => {
+		const component = new Mount({
+			target: document.querySelector('#target'),
+			props: {},
+		});
+	});
+</script>
+
+<div id="target" />