Merge branch 'main' into each-branch-manager

Rich-Harris · web-flow · commit 21c48dab48e8 · 2025-11-15T21:18:24.000-05:00
diff --git a/.changeset/cold-beds-look.md b/.changeset/cold-beds-look.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: properly defer document title until async work is complete
diff --git a/.changeset/ready-flies-invite.md b/.changeset/ready-flies-invite.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: take blockers of components into account
diff --git a/packages/svelte/src/compiler/phases/1-parse/state/element.js b/packages/svelte/src/compiler/phases/1-parse/state/element.js
@@ -242,6 +242,10 @@ export default function element(parser) {
 		parser.allow_whitespace();
 	}
 
+	if (element.type === 'Component') {
+		element.metadata.expression = new ExpressionMetadata();
+	}
+
 	if (element.type === 'SvelteComponent') {
 		const index = element.attributes.findIndex(
 			/** @param {any} attr */
@@ -257,6 +261,7 @@ export default function element(parser) {
 		}
 
 		element.expression = get_attribute_expression(definition);
+		element.metadata.expression = new ExpressionMetadata();
 	}
 
 	if (element.type === 'SvelteElement') {
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/Component.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/Component.js
@@ -16,5 +16,11 @@ export function Component(node, context) {
 		binding !== null &&
 		(binding.kind !== 'normal' || node.name.includes('.'));
 
+	if (binding) {
+		node.metadata.expression.has_state = node.metadata.dynamic;
+		node.metadata.expression.dependencies.add(binding);
+		node.metadata.expression.references.add(binding);
+	}
+
 	visit_component(node, context);
 }
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteComponent.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteComponent.js
@@ -12,7 +12,7 @@ export function SvelteComponent(node, context) {
 		w.svelte_component_deprecated(node);
 	}
 
-	context.visit(node.expression);
+	context.visit(node.expression, { ...context.state, expression: node.metadata.expression });
 
 	visit_component(node, context);
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/TitleElement.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/TitleElement.js
@@ -29,17 +29,16 @@ export function TitleElement(node, context) {
 		)
 	);
 
-	// Always in an $effect so it only changes the title once async work is done
+	// Make sure it only changes the title once async work is done
 	if (has_state) {
 		context.state.after_update.push(
 			b.stmt(
 				b.call(
-					'$.template_effect',
+					'$.deferred_template_effect',
 					b.arrow(memoizer.apply(), b.block([statement])),
 					memoizer.sync_values(),
 					memoizer.async_values(),
-					memoizer.blockers(),
-					b.true
+					memoizer.blockers()
 				)
 			)
 		);
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js
@@ -451,6 +451,11 @@ export function build_component(node, component_name, context) {
 		};
 	}
 
+	if (node.type !== 'SvelteSelf') {
+		// Component name itself could be blocked on async values
+		memoizer.check_blockers(node.metadata.expression);
+	}
+
 	const statements = [...snippet_declarations, ...memoizer.deriveds(context.state.analysis.runes)];
 
 	if (is_component_dynamic) {
diff --git a/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/component.js b/packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/component.js
@@ -325,17 +325,26 @@ export function build_inline_component(node, expression, context) {
 		);
 	}
 
+	if (node.type !== 'SvelteSelf') {
+		// Component name itself could be blocked on async values
+		optimiser.check_blockers(node.metadata.expression);
+	}
+
 	const is_async = optimiser.is_async();
 
 	if (is_async) {
 		statement = create_async_block(
-			b.block([optimiser.apply(), statement]),
+			b.block([
+				optimiser.apply(),
+				dynamic && custom_css_props.length === 0
+					? b.stmt(b.call('$$renderer.push', empty_comment))
+					: b.empty,
+				statement
+			]),
 			optimiser.blockers(),
 			optimiser.has_await
 		);
-	}
-
-	if (dynamic && custom_css_props.length === 0) {
+	} else if (dynamic && custom_css_props.length === 0) {
 		context.state.template.push(empty_comment);
 	}
 
diff --git a/packages/svelte/src/compiler/types/template.d.ts b/packages/svelte/src/compiler/types/template.d.ts
@@ -308,6 +308,7 @@ export namespace AST {
 		type: 'Component';
 		/** @internal */
 		metadata: {
+			expression: ExpressionMetadata;
 			scopes: Record<string, Scope>;
 			dynamic: boolean;
 			/** The set of locally-defined snippets that this component tag could render,
@@ -355,6 +356,7 @@ export namespace AST {
 		expression: Expression;
 		/** @internal */
 		metadata: {
+			expression: ExpressionMetadata;
 			scopes: Record<string, Scope>;
 			/** The set of locally-defined snippets that this component tag could render,
 			 * used for CSS pruning purposes */
diff --git a/packages/svelte/src/internal/client/index.js b/packages/svelte/src/internal/client/index.js
@@ -119,6 +119,7 @@ export {
 	legacy_pre_effect_reset,
 	render_effect,
 	template_effect,
+	deferred_template_effect,
 	effect,
 	user_effect,
 	user_pre_effect
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -144,6 +144,10 @@ export class Batch {
 
 	is_fork = false;
 
+	is_deferred() {
+		return this.is_fork || this.#blocking_pending > 0;
+	}
+
 	/**
 	 *
 	 * @param {Effect[]} root_effects
@@ -172,7 +176,7 @@ export class Batch {
 			this.#resolve();
 		}
 
-		if (this.#blocking_pending > 0 || this.is_fork) {
+		if (this.is_deferred()) {
 			this.#defer_effects(target.effects);
 			this.#defer_effects(target.render_effects);
 			this.#defer_effects(target.block_effects);
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -40,7 +40,7 @@ import { DEV } from 'esm-env';
 import { define_property } from '../../shared/utils.js';
 import { get_next_sibling } from '../dom/operations.js';
 import { component_context, dev_current_component_function, dev_stack } from '../context.js';
-import { Batch, schedule_effect } from './batch.js';
+import { Batch, current_batch, schedule_effect } from './batch.js';
 import { flatten } from './async.js';
 import { without_reactive_context } from '../dom/elements/bindings/shared.js';
 
@@ -363,11 +363,29 @@ export function render_effect(fn, flags = 0) {
  * @param {Array<() => any>} sync
  * @param {Array<() => Promise<any>>} async
  * @param {Array<Promise<void>>} blockers
- * @param {boolean} defer
  */
-export function template_effect(fn, sync = [], async = [], blockers = [], defer = false) {
+export function template_effect(fn, sync = [], async = [], blockers = []) {
 	flatten(blockers, sync, async, (values) => {
-		create_effect(defer ? EFFECT : RENDER_EFFECT, () => fn(...values.map(get)), true);
+		create_effect(RENDER_EFFECT, () => fn(...values.map(get)), true);
+	});
+}
+
+/**
+ * Like `template_effect`, but with an effect which is deferred until the batch commits
+ * @param {(...expressions: any) => void | (() => void)} fn
+ * @param {Array<() => any>} sync
+ * @param {Array<() => Promise<any>>} async
+ * @param {Array<Promise<void>>} blockers
+ */
+export function deferred_template_effect(fn, sync = [], async = [], blockers = []) {
+	var batch = /** @type {Batch} */ (current_batch);
+	var is_async = async.length > 0 || blockers.length > 0;
+
+	if (is_async) batch.increment(true);
+
+	flatten(blockers, sync, async, (values) => {
+		create_effect(EFFECT, () => fn(...values.map(get)), false);
+		if (is_async) batch.decrement(true);
 	});
 }
 
diff --git a/packages/svelte/tests/runtime-runes/samples/async-dynamic-component/Component.svelte b/packages/svelte/tests/runtime-runes/samples/async-dynamic-component/Component.svelte
@@ -0,0 +1 @@
+Hi
diff --git a/packages/svelte/tests/runtime-runes/samples/async-dynamic-component/_config.js b/packages/svelte/tests/runtime-runes/samples/async-dynamic-component/_config.js
@@ -0,0 +1,11 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['async-server', 'client', 'hydrate'],
+	ssrHtml: 'Hi Hi Hi Hi',
+	async test({ assert, target }) {
+		await tick();
+		assert.htmlEqual(target.innerHTML, 'Hi Hi Hi Hi');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-dynamic-component/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-dynamic-component/main.svelte
@@ -0,0 +1,10 @@
+<script>
+	import Component from './Component.svelte'
+	const X = $derived(await Promise.resolve(Component))
+	const Y = await Promise.resolve(Component)
+</script>
+
+<X />
+<svelte:component this={X} />
+<Y />
+<svelte:component this={Y} />
diff --git a/packages/svelte/tests/runtime-runes/samples/async-head-title-3/Inner.svelte b/packages/svelte/tests/runtime-runes/samples/async-head-title-3/Inner.svelte
@@ -0,0 +1,15 @@
+<script>
+	let { deferred, title } = $props();
+
+	function push() {
+		const d = Promise.withResolvers();
+		deferred.push(() => d.resolve());
+		return d.promise;
+	}
+</script>
+
+<svelte:head>
+	<title>{title}</title>
+</svelte:head>
+
+<p>{await push()}</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-head-title-3/_config.js b/packages/svelte/tests/runtime-runes/samples/async-head-title-3/_config.js
@@ -0,0 +1,24 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [toggle, resolve] = target.querySelectorAll('button');
+		toggle.click();
+		await tick();
+		assert.equal(window.document.title, '');
+
+		toggle.click();
+		await tick();
+		assert.equal(window.document.title, '');
+
+		toggle.click();
+		await tick();
+		assert.equal(window.document.title, '');
+
+		resolve.click();
+		await tick();
+		await tick();
+		assert.equal(window.document.title, 'title');
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-head-title-3/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-head-title-3/main.svelte
@@ -0,0 +1,12 @@
+<script>
+	import Inner from './Inner.svelte';
+
+	let deferred = [];
+	let show = $state(false);
+</script>
+
+<button onclick={() => show = !show}>toggle</button>
+<button onclick={() => deferred.pop()()}>resolve</button>
+{#if show}
+	<Inner {deferred} title="title" />
+{/if}

-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +---
 +'svelte': patch
 +---
++
 +fix: properly defer document title until async work is complete
Original file line number	Diff line number	Diff line change
`@@ -242,6 +242,10 @@ export default function element(parser) {`
`242`	`242`	`parser.allow_whitespace();`
`243`	`243`	`}`
`244`	`244`
	`245`	`+ if (element.type === 'Component') {`
	`246`	`+ element.metadata.expression = new ExpressionMetadata();`
	`247`	`+ }`
	`248`	`+`
`245`	`249`	`if (element.type === 'SvelteComponent') {`
`246`	`250`	`const index = element.attributes.findIndex(`
`247`	`251`	`/** @param {any} attr */`
`@@ -257,6 +261,7 @@ export default function element(parser) {`
`257`	`261`	`}`
`258`	`262`
`259`	`263`	`element.expression = get_attribute_expression(definition);`
	`264`	`+ element.metadata.expression = new ExpressionMetadata();`
`260`	`265`	`}`
`261`	`266`
`262`	`267`	`if (element.type === 'SvelteElement') {`
Original file line number	Diff line number	Diff line change
`@@ -12,7 +12,7 @@ export function SvelteComponent(node, context) {`
`12`	`12`	`w.svelte_component_deprecated(node);`
`13`	`13`	`}`
`14`	`14`
`15`		`- context.visit(node.expression);`
	`15`	`+ context.visit(node.expression, { ...context.state, expression: node.metadata.expression });`
`16`	`16`
`17`	`17`	`visit_component(node, context);`
`18`	`18`	`}`