tweak/fix

Author: Rich-Harris

packages/svelte/src/internal/client/dom/blocks/async.js

@@ -22,14 +22,15 @@ export function async(node, expressions, fn) {
 	boundary.increment();
 
 	Promise.all(expressions.map((fn) => async_derived(fn))).then((result) => {
-		batch.run(() => {
-			restore();
-			fn(node, ...result);
+		batch?.restore();
 
-			// TODO is this necessary?
-			schedule_effect(effect);
-		});
+		restore();
+		fn(node, ...result);
 
+		// TODO is this necessary?
+		schedule_effect(effect);
+
+		batch?.flush();
 		boundary.decrement();
 	});
 }

packages/svelte/src/internal/client/reactivity/batch.js

@@ -2,6 +2,7 @@
 import { CLEAN, DIRTY } from '#client/constants';
 import {
 	flush_queued_effects,
+	flush_queued_root_effects,
 	process_effects,
 	schedule_effect,
 	set_queued_root_effects,
@@ -17,10 +18,6 @@ const batches = new Set();
 /** @type {Batch | null} */
 export let current_batch = null;
 
-export function remove_current_batch() {
-	current_batch = null;
-}
-
 /** Update `$effect.pending()` */
 function update_pending() {
 	internal_set(pending, batches.size > 0);
@@ -149,12 +146,21 @@ export class Batch {
 		}
 	}
 
-	/**
-	 * @param {() => void} fn
-	 */
-	run(fn) {
+	restore() {
 		current_batch = this;
-		fn();
+	}
+
+	flush() {
+		flush_queued_root_effects();
+
+		// TODO can this happen?
+		if (current_batch !== this) return;
+
+		if (this.settled()) {
+			this.remove();
+		}
+
+		current_batch = null;
 	}
 
 	commit() {
@@ -210,6 +216,15 @@ export class Batch {
 
 			current_batch = new Batch();
 			batches.add(current_batch);
+
+			queueMicrotask(() => {
+				if (current_batch === null) {
+					// a flushSync happened in the meantime
+					return;
+				}
+
+				current_batch.flush();
+			});
 		}
 
 		return current_batch;

packages/svelte/src/internal/client/reactivity/deriveds.js

@@ -162,9 +162,9 @@ export function async_derived(fn, location) {
 					}
 				}
 
-				batch.run(() => {
-					internal_set(signal, v);
-				});
+				batch?.restore();
+				internal_set(signal, v);
+				batch?.flush();
 
 				if (DEV && location !== undefined) {
 					recent_async_deriveds.add(signal);

packages/svelte/src/internal/client/reactivity/effects.js

@@ -357,9 +357,9 @@ export function template_effect(fn, sync = [], async = [], d = derived) {
 
 			var effect = create_template_effect(fn, [...sync.map(d), ...result]);
 
-			batch.run(() => {
-				schedule_effect(effect);
-			});
+			batch?.restore();
+			schedule_effect(effect);
+			batch?.flush();
 		});
 	} else {
 		create_template_effect(fn, sync.map(d));

packages/svelte/src/internal/client/runtime.js

@@ -51,7 +51,7 @@ import {
 import { Boundary } from './dom/blocks/boundary.js';
 import * as w from './warnings.js';
 import { is_firefox } from './dom/operations.js';
-import { current_batch, Batch, remove_current_batch } from './reactivity/batch.js';
+import { current_batch, Batch } from './reactivity/batch.js';
 import { log_effect_tree, root } from './dev/debug.js';
 
 // Used for DEV time error handling
@@ -693,7 +693,7 @@ function infinite_loop_guard() {
 	}
 }
 
-function flush_queued_root_effects() {
+export function flush_queued_root_effects() {
 	var was_updating_effect = is_updating_effect;
 	var batch = /** @type {Batch} */ (current_batch);
 
@@ -764,24 +764,6 @@ export function flush_queued_effects(effects) {
  * @returns {void}
  */
 export function schedule_effect(signal) {
-	if (!is_flushing) {
-		is_flushing = true;
-		queueMicrotask(() => {
-			if (current_batch === null) {
-				// a flushSync happened in the meantime
-				return;
-			}
-
-			flush_queued_root_effects();
-
-			if (current_batch?.settled()) {
-				current_batch.remove();
-			}
-
-			remove_current_batch();
-		});
-	}
-
 	var effect = (last_scheduled_effect = signal);
 
 	while (effect.parent !== null) {
@@ -868,7 +850,7 @@ export function process_effects(batch, root) {
 export function flushSync(fn) {
 	var result;
 
-	Batch.ensure();
+	const batch = Batch.ensure();
 
 	if (fn) {
 		is_flushing = true;
@@ -884,12 +866,10 @@ export function flushSync(fn) {
 		flush_tasks();
 	}
 
-	if (current_batch?.settled()) {
-		current_batch.remove();
+	if (batch === current_batch) {
+		batch.flush();
 	}
 
-	remove_current_batch();
-
 	return /** @type {T} */ (result);
 }