From bc4dc1d10d54ecbc61398a248f8a45a4f4bcfa13 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Wed, 4 Feb 2026 10:28:32 +0100
Subject: [PATCH 1/6] fix: avoid erroneous async derived expressions for blocks
 (#17604)

fixes #17595

When an if/key/etc block has an expression that depends on an async blocker (e.g., is inside a component with top level `await`), the compiler incorrectly treats the expression as async - even when the expression itself contains no `await`.

This causes the expression to be added to `$.async`'s `expressions` array, which wraps it in an `async_derived`. This is not only unnecessary but also buggy: it breaks the direct reactive connection between the source and its dependent effects, causing inconsistent effect executions.

The fix is to only add expressions to `$.async`'s `expressions` array when they actually contain an `await`.

When a branch is speculatively marked for destruction (condition temporarily falsy), its child effects are reset to `CLEAN` to prevent them running in a doomed branch (as of #17581). However, if the branch survives (condition becomes truthy again), those effects remain `CLEAN` and never run - the source was already marked dirty before the reset, so no new dirty marking occurs.

The fix is to change `skipped_effects` from a `Set` to a `Map` that tracks which child effects were dirty/maybe_dirty before being reset. When a branch is unskipped (survives), restore their status and reschedule them.

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .changeset/some-teams-pay.md                  |  5 ++
 .changeset/yummy-insects-wonder.md            |  5 ++
 .../3-transform/client/visitors/EachBlock.js  | 15 +++--
 .../3-transform/client/visitors/HtmlTag.js    | 14 ++--
 .../3-transform/client/visitors/IfBlock.js    | 14 ++--
 .../3-transform/client/visitors/KeyBlock.js   | 32 +++++----
 .../client/visitors/SvelteElement.js          | 14 ++--
 .../internal/client/dom/blocks/branches.js    |  8 +--
 .../src/internal/client/dom/blocks/each.js    |  4 +-
 .../src/internal/client/reactivity/batch.js   | 65 +++++++++++++++----
 .../svelte/tests/runtime-legacy/shared.ts     |  4 +-
 .../Child.svelte                              |  9 +++
 .../_config.js                                | 16 +++++
 .../main.svelte                               | 14 ++++
 14 files changed, 166 insertions(+), 53 deletions(-)
 create mode 100644 .changeset/some-teams-pay.md
 create mode 100644 .changeset/yummy-insects-wonder.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-derived-unmount-undefined-props/Child.svelte
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-derived-unmount-undefined-props/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-derived-unmount-undefined-props/main.svelte

diff --git a/.changeset/some-teams-pay.md b/.changeset/some-teams-pay.md
new file mode 100644
index 0000000000..d7ae69566d
--- /dev/null
+++ b/.changeset/some-teams-pay.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: avoid erroneous async derived expressions for blocks
diff --git a/.changeset/yummy-insects-wonder.md b/.changeset/yummy-insects-wonder.md
new file mode 100644
index 0000000000..6e705cd8cf
--- /dev/null
+++ b/.changeset/yummy-insects-wonder.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: reschedule effects inside unskipped branches
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
index c0bfe272e5..1dbc34fdc3 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
@@ -312,10 +312,10 @@ export function EachBlock(node, context) {
 		declarations.push(b.let(node.index, index));
 	}
 
-	const is_async = node.metadata.expression.is_async();
+	const has_await = node.metadata.expression.has_await;
 
-	const get_collection = b.thunk(collection, node.metadata.expression.has_await);
-	const thunk = is_async ? b.thunk(b.call('$.get', b.id('$$collection'))) : get_collection;
+	const get_collection = b.thunk(collection, has_await);
+	const thunk = has_await ? b.thunk(b.call('$.get', b.id('$$collection'))) : get_collection;
 
 	const render_args = [b.id('$$anchor'), item];
 	if (uses_index || collection_id) render_args.push(index);
@@ -342,15 +342,18 @@ export function EachBlock(node, context) {
 		statements.unshift(b.stmt(b.call('$.validate_each_keys', thunk, key_function)));
 	}
 
-	if (is_async) {
+	if (node.metadata.expression.is_async()) {
 		context.state.init.push(
 			b.stmt(
 				b.call(
 					'$.async',
 					context.state.node,
 					node.metadata.expression.blockers(),
-					b.array([get_collection]),
-					b.arrow([context.state.node, b.id('$$collection')], b.block(statements))
+					has_await ? b.array([get_collection]) : b.void0,
+					b.arrow(
+						has_await ? [context.state.node, b.id('$$collection')] : [context.state.node],
+						b.block(statements)
+					)
 				)
 			)
 		);
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/HtmlTag.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/HtmlTag.js
index 0567edc610..2706cf7f0a 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/HtmlTag.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/HtmlTag.js
@@ -11,10 +11,11 @@ import { build_expression } from './shared/utils.js';
 export function HtmlTag(node, context) {
 	context.state.template.push_comment();
 
-	const is_async = node.metadata.expression.is_async();
+	const has_await = node.metadata.expression.has_await;
+	const has_blockers = node.metadata.expression.has_blockers();
 
 	const expression = build_expression(context, node.expression, node.metadata.expression);
-	const html = is_async ? b.call('$.get', b.id('$$html')) : expression;
+	const html = has_await ? b.call('$.get', b.id('$$html')) : expression;
 
 	const is_svg = context.state.metadata.namespace === 'svg';
 	const is_mathml = context.state.metadata.namespace === 'mathml';
@@ -31,15 +32,18 @@ export function HtmlTag(node, context) {
 	);
 
 	// push into init, so that bindings run afterwards, which might trigger another run and override hydration
-	if (is_async) {
+	if (has_await || has_blockers) {
 		context.state.init.push(
 			b.stmt(
 				b.call(
 					'$.async',
 					context.state.node,
 					node.metadata.expression.blockers(),
-					b.array([b.thunk(expression, node.metadata.expression.has_await)]),
-					b.arrow([context.state.node, b.id('$$html')], b.block([statement]))
+					has_await ? b.array([b.thunk(expression, true)]) : b.void0,
+					b.arrow(
+						has_await ? [context.state.node, b.id('$$html')] : [context.state.node],
+						b.block([statement])
+					)
 				)
 			)
 		);
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/IfBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/IfBlock.js
index fcbb59ba74..c0e66635df 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/IfBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/IfBlock.js
@@ -25,10 +25,11 @@ export function IfBlock(node, context) {
 		statements.push(b.var(alternate_id, b.arrow([b.id('$$anchor')], alternate)));
 	}
 
-	const is_async = node.metadata.expression.is_async();
+	const has_await = node.metadata.expression.has_await;
+	const has_blockers = node.metadata.expression.has_blockers();
 
 	const expression = build_expression(context, node.test, node.metadata.expression);
-	const test = is_async ? b.call('$.get', b.id('$$condition')) : expression;
+	const test = has_await ? b.call('$.get', b.id('$$condition')) : expression;
 
 	/** @type {Expression[]} */
 	const args = [
@@ -72,15 +73,18 @@ export function IfBlock(node, context) {
 
 	statements.push(add_svelte_meta(b.call('$.if', ...args), node, 'if'));
 
-	if (is_async) {
+	if (has_await || has_blockers) {
 		context.state.init.push(
 			b.stmt(
 				b.call(
 					'$.async',
 					context.state.node,
 					node.metadata.expression.blockers(),
-					b.array([b.thunk(expression, node.metadata.expression.has_await)]),
-					b.arrow([context.state.node, b.id('$$condition')], b.block(statements))
+					has_await ? b.array([b.thunk(expression, true)]) : b.void0,
+					b.arrow(
+						has_await ? [context.state.node, b.id('$$condition')] : [context.state.node],
+						b.block(statements)
+					)
 				)
 			)
 		);
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/KeyBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/KeyBlock.js
index d050155e8b..143a4e8edd 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/KeyBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/KeyBlock.js
@@ -11,29 +11,35 @@ import { build_expression, add_svelte_meta } from './shared/utils.js';
 export function KeyBlock(node, context) {
 	context.state.template.push_comment();
 
-	const is_async = node.metadata.expression.is_async();
+	const has_await = node.metadata.expression.has_await;
+	const has_blockers = node.metadata.expression.has_blockers();
 
 	const expression = build_expression(context, node.expression, node.metadata.expression);
-	const key = b.thunk(is_async ? b.call('$.get', b.id('$$key')) : expression);
+	const key = b.thunk(has_await ? b.call('$.get', b.id('$$key')) : expression);
 	const body = /** @type {Expression} */ (context.visit(node.fragment));
 
-	let statement = add_svelte_meta(
+	const statement = add_svelte_meta(
 		b.call('$.key', context.state.node, key, b.arrow([b.id('$$anchor')], body)),
 		node,
 		'key'
 	);
 
-	if (is_async) {
-		statement = b.stmt(
-			b.call(
-				'$.async',
-				context.state.node,
-				node.metadata.expression.blockers(),
-				b.array([b.thunk(expression, node.metadata.expression.has_await)]),
-				b.arrow([context.state.node, b.id('$$key')], b.block([statement]))
+	if (has_await || has_blockers) {
+		context.state.init.push(
+			b.stmt(
+				b.call(
+					'$.async',
+					context.state.node,
+					node.metadata.expression.blockers(),
+					has_await ? b.array([b.thunk(expression, true)]) : b.void0,
+					b.arrow(
+						has_await ? [context.state.node, b.id('$$key')] : [context.state.node],
+						b.block([statement])
+					)
+				)
 			)
 		);
+	} else {
+		context.state.init.push(statement);
 	}
-
-	context.state.init.push(statement);
 }
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteElement.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteElement.js
index c8192cf00a..10024298fa 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteElement.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteElement.js
@@ -93,10 +93,11 @@ export function SvelteElement(node, context) {
 		);
 	}
 
-	const is_async = node.metadata.expression.is_async();
+	const has_await = node.metadata.expression.has_await;
+	const has_blockers = node.metadata.expression.has_blockers();
 
 	const expression = /** @type {Expression} */ (context.visit(node.tag));
-	const get_tag = b.thunk(is_async ? b.call('$.get', b.id('$$tag')) : expression);
+	const get_tag = b.thunk(has_await ? b.call('$.get', b.id('$$tag')) : expression);
 
 	/** @type {Statement[]} */
 	const inner = inner_context.state.init;
@@ -139,15 +140,18 @@ export function SvelteElement(node, context) {
 		)
 	);
 
-	if (is_async) {
+	if (has_await || has_blockers) {
 		context.state.init.push(
 			b.stmt(
 				b.call(
 					'$.async',
 					context.state.node,
 					node.metadata.expression.blockers(),
-					b.array([b.thunk(expression, node.metadata.expression.has_await)]),
-					b.arrow([context.state.node, b.id('$$tag')], b.block(statements))
+					has_await ? b.array([b.thunk(expression, true)]) : b.void0,
+					b.arrow(
+						has_await ? [context.state.node, b.id('$$tag')] : [context.state.node],
+						b.block(statements)
+					)
 				)
 			)
 		);
diff --git a/packages/svelte/src/internal/client/dom/blocks/branches.js b/packages/svelte/src/internal/client/dom/blocks/branches.js
index 527f0b0a8f..6b77903574 100644
--- a/packages/svelte/src/internal/client/dom/blocks/branches.js
+++ b/packages/svelte/src/internal/client/dom/blocks/branches.js
@@ -200,17 +200,17 @@ export class BranchManager {
 		if (defer) {
 			for (const [k, effect] of this.#onscreen) {
 				if (k === key) {
-					batch.skipped_effects.delete(effect);
+					batch.unskip_effect(effect);
 				} else {
-					batch.skipped_effects.add(effect);
+					batch.skip_effect(effect);
 				}
 			}
 
 			for (const [k, branch] of this.#offscreen) {
 				if (k === key) {
-					batch.skipped_effects.delete(branch.effect);
+					batch.unskip_effect(branch.effect);
 				} else {
-					batch.skipped_effects.add(branch.effect);
+					batch.skip_effect(branch.effect);
 				}
 			}
 
diff --git a/packages/svelte/src/internal/client/dom/blocks/each.js b/packages/svelte/src/internal/client/dom/blocks/each.js
index 232656ec11..6eaeac0f38 100644
--- a/packages/svelte/src/internal/client/dom/blocks/each.js
+++ b/packages/svelte/src/internal/client/dom/blocks/each.js
@@ -257,7 +257,7 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 				if (item.i) internal_set(item.i, index);
 
 				if (defer) {
-					batch.skipped_effects.delete(item.e);
+					batch.unskip_effect(item.e);
 				}
 			} else {
 				item = create_item(
@@ -299,7 +299,7 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 			if (defer) {
 				for (const [key, item] of items) {
 					if (!keys.has(key)) {
-						batch.skipped_effects.add(item.e);
+						batch.skip_effect(item.e);
 					}
 				}
 
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index 2b6e84889b..cef2df4716 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -130,11 +130,13 @@ export class Batch {
 	#maybe_dirty_effects = new Set();
 
 	/**
-	 * A set of branches that still exist, but will be destroyed when this batch
-	 * is committed — we skip over these during `process`
-	 * @type {Set<Effect>}
+	 * A map of branches that still exist, but will be destroyed when this batch
+	 * is committed — we skip over these during `process`.
+	 * The value contains child effects that were dirty/maybe_dirty before being reset,
+	 * so they can be rescheduled if the branch survives.
+	 * @type {Map<Effect, { d: Effect[], m: Effect[] }>}
 	 */
-	skipped_effects = new Set();
+	#skipped_branches = new Map();
 
 	is_fork = false;
 
@@ -144,6 +146,38 @@ export class Batch {
 		return this.is_fork || this.#blocking_pending > 0;
 	}
 
+	/**
+	 * Add an effect to the #skipped_branches map and reset its children
+	 * @param {Effect} effect
+	 */
+	skip_effect(effect) {
+		if (!this.#skipped_branches.has(effect)) {
+			this.#skipped_branches.set(effect, { d: [], m: [] });
+		}
+	}
+
+	/**
+	 * Remove an effect from the #skipped_branches map and reschedule
+	 * any tracked dirty/maybe_dirty child effects
+	 * @param {Effect} effect
+	 */
+	unskip_effect(effect) {
+		var tracked = this.#skipped_branches.get(effect);
+		if (tracked) {
+			this.#skipped_branches.delete(effect);
+
+			for (var e of tracked.d) {
+				set_signal_status(e, DIRTY);
+				schedule_effect(e);
+			}
+
+			for (e of tracked.m) {
+				set_signal_status(e, MAYBE_DIRTY);
+				schedule_effect(e);
+			}
+		}
+	}
+
 	/**
 	 *
 	 * @param {Effect[]} root_effects
@@ -172,8 +206,8 @@ export class Batch {
 			this.#defer_effects(render_effects);
 			this.#defer_effects(effects);
 
-			for (const e of this.skipped_effects) {
-				reset_branch(e);
+			for (const [e, t] of this.#skipped_branches) {
+				reset_branch(e, t);
 			}
 		} else {
 			// append/remove branches
@@ -220,7 +254,7 @@ export class Batch {
 			var is_branch = (flags & (BRANCH_EFFECT | ROOT_EFFECT)) !== 0;
 			var is_skippable_branch = is_branch && (flags & CLEAN) !== 0;
 
-			var skip = is_skippable_branch || (flags & INERT) !== 0 || this.skipped_effects.has(effect);
+			var skip = is_skippable_branch || (flags & INERT) !== 0 || this.#skipped_branches.has(effect);
 
 			// Inside a `<svelte:boundary>` with a pending snippet,
 			// all effects are deferred until the boundary resolves
@@ -807,7 +841,8 @@ export function schedule_effect(signal) {
 		var flags = effect.f;
 
 		// if the effect is being scheduled because a parent (each/await/etc) block
-		// updated an internal source, bail out or we'll cause a second flush
+		// updated an internal source, or because a branch is being unskipped,
+		// bail out or we'll cause a second flush
 		if (
 			is_flushing &&
 			effect === active_effect &&
@@ -887,20 +922,28 @@ export function eager(fn) {
 
 /**
  * Mark all the effects inside a skipped branch CLEAN, so that
- * they can be correctly rescheduled later
+ * they can be correctly rescheduled later. Tracks dirty and maybe_dirty
+ * effects so they can be rescheduled if the branch survives.
  * @param {Effect} effect
+ * @param {{ d: Effect[], m: Effect[] }} tracked
  */
-function reset_branch(effect) {
+function reset_branch(effect, tracked) {
 	// clean branch = nothing dirty inside, no need to traverse further
 	if ((effect.f & BRANCH_EFFECT) !== 0 && (effect.f & CLEAN) !== 0) {
 		return;
 	}
 
+	if ((effect.f & DIRTY) !== 0) {
+		tracked.d.push(effect);
+	} else if ((effect.f & MAYBE_DIRTY) !== 0) {
+		tracked.m.push(effect);
+	}
+
 	set_signal_status(effect, CLEAN);
 
 	var e = effect.first;
 	while (e !== null) {
-		reset_branch(e);
+		reset_branch(e, tracked);
 		e = e.next;
 	}
 }
diff --git a/packages/svelte/tests/runtime-legacy/shared.ts b/packages/svelte/tests/runtime-legacy/shared.ts
index 13975c68ee..8c29a6ada2 100644
--- a/packages/svelte/tests/runtime-legacy/shared.ts
+++ b/packages/svelte/tests/runtime-legacy/shared.ts
@@ -47,9 +47,9 @@ export interface RuntimeTest<Props extends Record<string, any> = Record<string,
 	mode?: Array<'server' | 'async-server' | 'client' | 'hydrate'>;
 	/** Temporarily skip specific modes, without skipping the entire test */
 	skip_mode?: Array<'server' | 'async-server' | 'client' | 'hydrate'>;
-	/** Skip if running with process.env.NO_ASYNC */
+	/** Skip if running with process.env.SVELTE_NO_ASYNC */
 	skip_no_async?: boolean;
-	/** Skip if running without process.env.NO_ASYNC */
+	/** Skip if running without process.env.SVELTE_NO_ASYNC */
 	skip_async?: boolean;
 	html?: string;
 	ssrHtml?: string;
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-unmount-undefined-props/Child.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived-unmount-undefined-props/Child.svelte
new file mode 100644
index 0000000000..fecbe222e3
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-unmount-undefined-props/Child.svelte
@@ -0,0 +1,9 @@
+<script>
+	let { id } = $props();
+
+	// BUG: This logs 'undefined' on unmount when parent has async derived
+	const data = $derived(await Promise.resolve(id).then((x) => {
+		console.log('promise resolved with:', x);
+		return x;
+	}));
+</script>
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-unmount-undefined-props/_config.js b/packages/svelte/tests/runtime-runes/samples/async-derived-unmount-undefined-props/_config.js
new file mode 100644
index 0000000000..2f371bc6b7
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-unmount-undefined-props/_config.js
@@ -0,0 +1,16 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, logs }) {
+		await tick();
+
+		assert.deepEqual(logs, ['promise resolved with:', 'some-id']);
+
+		const button = target.querySelector('button');
+		button?.click();
+		await tick();
+
+		assert.deepEqual(logs, ['promise resolved with:', 'some-id']);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-derived-unmount-undefined-props/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-derived-unmount-undefined-props/main.svelte
new file mode 100644
index 0000000000..d5cdd5967e
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-derived-unmount-undefined-props/main.svelte
@@ -0,0 +1,14 @@
+<script>
+	import Child from './Child.svelte';
+
+	// This async derived in parent triggers the bug
+	const something = $derived(await Promise.resolve('test'));
+
+	let active = $state('some-id');
+</script>
+
+{#if active}
+	<Child id={active} />
+{/if}
+
+<button onclick={() => active = undefined}>close</button>

From baba15ab981a3b090eaabefe3425f5f4ea9a8074 Mon Sep 17 00:00:00 2001
From: Tee Ming <chewteeming01@gmail.com>
Date: Thu, 5 Feb 2026 00:31:33 +0800
Subject: [PATCH 2/6] fix: avoid 'node:crypto' cloudflare warnings (#17612)

* fix: avoid 'node:crypto' cloudflare warnings

* format

* changeset

* Apply suggestion from @teemingc
---
 .changeset/violet-pans-know.md                | 5 +++++
 packages/svelte/src/internal/server/crypto.js | 3 ++-
 2 files changed, 7 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/violet-pans-know.md

diff --git a/.changeset/violet-pans-know.md b/.changeset/violet-pans-know.md
new file mode 100644
index 0000000000..59bf1dcaaf
--- /dev/null
+++ b/.changeset/violet-pans-know.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: avoid Cloudflare warnings about not having the "node:crypto" module
diff --git a/packages/svelte/src/internal/server/crypto.js b/packages/svelte/src/internal/server/crypto.js
index 8727635481..9bb6ecdd39 100644
--- a/packages/svelte/src/internal/server/crypto.js
+++ b/packages/svelte/src/internal/server/crypto.js
@@ -12,7 +12,8 @@ export async function sha256(data) {
 	crypto ??= globalThis.crypto?.subtle?.digest
 		? globalThis.crypto
 		: // @ts-ignore - we don't install node types in the prod build
-			(await import('node:crypto')).webcrypto;
+			// don't use 'node:crypto' because static analysers will think we rely on node when we don't
+			(await import('node:' + 'crypto')).webcrypto;
 
 	const hash_buffer = await crypto.subtle.digest('SHA-256', text_encoder.encode(data));
 

From 05229d96823cc88d11c0b4a81b357cdb67f69326 Mon Sep 17 00:00:00 2001
From: Tee Ming <chewteeming01@gmail.com>
Date: Thu, 5 Feb 2026 00:32:33 +0800
Subject: [PATCH 3/6] chore: remove SvelteKit data attributes from
 elements.d.ts (#17613)

* Remove SvelteKit data attributes from elements.d.ts

Removed SvelteKit specific data attributes from elements.d.ts.

* Remove SvelteKit data attributes from elements.d.ts

Removed SvelteKit data attributes from elements.d.ts.

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
---
 .changeset/quiet-buttons-bathe.md |  5 +++++
 packages/svelte/elements.d.ts     | 17 -----------------
 2 files changed, 5 insertions(+), 17 deletions(-)
 create mode 100644 .changeset/quiet-buttons-bathe.md

diff --git a/.changeset/quiet-buttons-bathe.md b/.changeset/quiet-buttons-bathe.md
new file mode 100644
index 0000000000..419a5569b4
--- /dev/null
+++ b/.changeset/quiet-buttons-bathe.md
@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+chore: remove SvelteKit data attributes from elements.d.ts
diff --git a/packages/svelte/elements.d.ts b/packages/svelte/elements.d.ts
index fa74124472..885004dd2a 100644
--- a/packages/svelte/elements.d.ts
+++ b/packages/svelte/elements.d.ts
@@ -851,23 +851,6 @@ export interface HTMLAttributes<T extends EventTarget> extends AriaAttributes, D
 	readonly 'bind:offsetWidth'?: number | undefined | null;
 	readonly 'bind:offsetHeight'?: number | undefined | null;
 
-	// SvelteKit
-	'data-sveltekit-keepfocus'?: true | '' | 'off' | undefined | null;
-	'data-sveltekit-noscroll'?: true | '' | 'off' | undefined | null;
-	'data-sveltekit-preload-code'?:
-		| true
-		| ''
-		| 'eager'
-		| 'viewport'
-		| 'hover'
-		| 'tap'
-		| 'off'
-		| undefined
-		| null;
-	'data-sveltekit-preload-data'?: true | '' | 'hover' | 'tap' | 'off' | undefined | null;
-	'data-sveltekit-reload'?: true | '' | 'off' | undefined | null;
-	'data-sveltekit-replacestate'?: true | '' | 'off' | undefined | null;
-
 	// allow any data- attribute
 	[key: `data-${string}`]: any;
 

From eb63a6bbbaffec07890ae181b02edf4c52e2586a Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Wed, 4 Feb 2026 11:52:30 -0500
Subject: [PATCH 4/6] Version Packages (#17614)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/quiet-buttons-bathe.md  |  5 -----
 .changeset/some-teams-pay.md       |  5 -----
 .changeset/violet-pans-know.md     |  5 -----
 .changeset/yummy-insects-wonder.md |  5 -----
 packages/svelte/CHANGELOG.md       | 12 ++++++++++++
 packages/svelte/package.json       |  2 +-
 packages/svelte/src/version.js     |  2 +-
 7 files changed, 14 insertions(+), 22 deletions(-)
 delete mode 100644 .changeset/quiet-buttons-bathe.md
 delete mode 100644 .changeset/some-teams-pay.md
 delete mode 100644 .changeset/violet-pans-know.md
 delete mode 100644 .changeset/yummy-insects-wonder.md

diff --git a/.changeset/quiet-buttons-bathe.md b/.changeset/quiet-buttons-bathe.md
deleted file mode 100644
index 419a5569b4..0000000000
--- a/.changeset/quiet-buttons-bathe.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-"svelte": patch
----
-
-chore: remove SvelteKit data attributes from elements.d.ts
diff --git a/.changeset/some-teams-pay.md b/.changeset/some-teams-pay.md
deleted file mode 100644
index d7ae69566d..0000000000
--- a/.changeset/some-teams-pay.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: avoid erroneous async derived expressions for blocks
diff --git a/.changeset/violet-pans-know.md b/.changeset/violet-pans-know.md
deleted file mode 100644
index 59bf1dcaaf..0000000000
--- a/.changeset/violet-pans-know.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: avoid Cloudflare warnings about not having the "node:crypto" module
diff --git a/.changeset/yummy-insects-wonder.md b/.changeset/yummy-insects-wonder.md
deleted file mode 100644
index 6e705cd8cf..0000000000
--- a/.changeset/yummy-insects-wonder.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: reschedule effects inside unskipped branches
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index c7c38302e8..a71effd5dd 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,17 @@
 # svelte
 
+## 5.49.2
+
+### Patch Changes
+
+- chore: remove SvelteKit data attributes from elements.d.ts ([#17613](https://github.com/sveltejs/svelte/pull/17613))
+
+- fix: avoid erroneous async derived expressions for blocks ([#17604](https://github.com/sveltejs/svelte/pull/17604))
+
+- fix: avoid Cloudflare warnings about not having the "node:crypto" module ([#17612](https://github.com/sveltejs/svelte/pull/17612))
+
+- fix: reschedule effects inside unskipped branches ([#17604](https://github.com/sveltejs/svelte/pull/17604))
+
 ## 5.49.1
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index fd4b98679e..48f492783f 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.49.1",
+  "version": "5.49.2",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 557b1ff156..31538c3fe7 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.49.1';
+export const VERSION = '5.49.2';
 export const PUBLIC_VERSION = '5';

From 4f41e816baa007fb6a4e31164da49576e87e342e Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 4 Feb 2026 13:07:46 -0500
Subject: [PATCH 5/6] fix: ensure infinite effect loops are cleared after
 flushing (#17601)

* failing effect-loop-infinite test

* fix
---
 .changeset/chatty-mammals-find.md                     |  5 +++++
 .../svelte/src/internal/client/reactivity/batch.js    |  3 ++-
 packages/svelte/tests/runtime-legacy/shared.ts        |  2 ++
 .../samples/effect-loop-infinite/_config.js           | 11 ++++++-----
 4 files changed, 15 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/chatty-mammals-find.md

diff --git a/.changeset/chatty-mammals-find.md b/.changeset/chatty-mammals-find.md
new file mode 100644
index 0000000000..373dc0059a
--- /dev/null
+++ b/.changeset/chatty-mammals-find.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure infinite effect loops are cleared after flushing
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index cef2df4716..9bf93c873f 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -647,8 +647,9 @@ function flush_effects() {
 			}
 		}
 	} finally {
-		is_flushing = false;
+		queued_root_effects = [];
 
+		is_flushing = false;
 		last_scheduled_effect = null;
 
 		if (DEV) {
diff --git a/packages/svelte/tests/runtime-legacy/shared.ts b/packages/svelte/tests/runtime-legacy/shared.ts
index 8c29a6ada2..c5317f822e 100644
--- a/packages/svelte/tests/runtime-legacy/shared.ts
+++ b/packages/svelte/tests/runtime-legacy/shared.ts
@@ -521,6 +521,8 @@ async function run_test_variant(
 						errors,
 						hydrate: hydrate_fn
 					});
+
+					flushSync();
 				}
 
 				if (config.runtime_error && !unhandled_rejection) {
diff --git a/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/_config.js b/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/_config.js
index 57f60c2b44..44cf5b09e2 100644
--- a/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/_config.js
@@ -11,11 +11,12 @@ export default test({
 	test({ assert, errors }) {
 		const [button] = document.querySelectorAll('button');
 
-		try {
+		assert.throws(() => {
 			flushSync(() => button.click());
-		} catch (e) {
-			assert.equal(errors.length, 1); // for whatever reason we can't get the name which should be 'updated at'
-			assert.ok(/** @type {Error} */ (e).message.startsWith('effect_update_depth_exceeded'));
-		}
+		}, /effect_update_depth_exceeded/);
+
+		assert.equal(errors.length, 1);
+
+		assert.doesNotThrow(flushSync);
 	}
 });

From d7a8e3d1300fbb802b84a6ebf0f3f71ed734a556 Mon Sep 17 00:00:00 2001
From: 7nik <kifiranet@gmail.com>
Date: Wed, 4 Feb 2026 21:51:50 +0200
Subject: [PATCH 6/6] fix: emit `each_key_duplicate` error in production
 (#16724)

* fix: emit `each_key_duplicate` error in production

* fix: preserve key

* Update packages/svelte/src/internal/client/dom/blocks/each.js

Co-authored-by: Rich Harris <rich.harris@vercel.com>

* Update packages/svelte/src/internal/client/dom/blocks/each.js

Co-authored-by: Rich Harris <rich.harris@vercel.com>

* fix: ensure keys are validated

* fix silly test name

* fix: cover other case of duplicate keys

* emit error on hydration

* ensure the error is handled

* drop useless tests

* unused

* finish merge

* add lost check back

* chore: bump playwright (#17565)

* chore: bump playwright

* maybe this will help somehow?

* err whatever

* fix

* chore: allow testing in production env 2 (#17590)

* Revert "chore: allow testing in production env (#16840)"

This reverts commit ffd65e90febc29feaca48e142126a4087fcaca9f.

* new approach

* fix: handle renderer.run rejections (#17591)

* fix: handle renderer run rejections

* add test

* changeset

* simplify

* explanatory comment

---------

Co-authored-by: Antonio Bennett <abennett@mabelslabels.com>
Co-authored-by: Rich Harris <rich.harris@vercel.com>

* fix: only create async functions in SSR output when necessary (#17593)

* fix: only create async functions in SSR output when necessary

* actually...

* simplify generated code a bit more

* simplify

* fix: merge consecutive text nodes during hydration for large text content (#17587)

* fix: merge consecutive text nodes during hydration for large text content

Fixes #17582

Browsers automatically split text nodes exceeding 65536 characters into
multiple consecutive text nodes during HTML parsing. This causes hydration
mismatches when Svelte expects a single text node.

The fix merges consecutive text nodes during hydration by:
- Detecting when the current node is a text node
- Finding all consecutive text node siblings
- Merging their content into the first text node
- Removing the extra text nodes

This restores correct hydration behavior for large text content.

* add test, fix

* fix

* fix

* changeset

---------

Co-authored-by: Miner <miner@example.com>
Co-authored-by: Rich Harris <rich.harris@vercel.com>

* Version Packages (#17585)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

* Revert "drop useless tests"

This reverts commit 65f77ef8409d6e8c91163f36853d36b05ec01ae8.

* update tests

* fix test

* we don't need to expose this function any more

* figured it out... we cant have errors during reconcile

* simplify

* tweak

* unused

* revert no-longer-needed change

* unused

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
Co-authored-by: Antonio Bennett <31296212+Antonio-Bennett@users.noreply.github.com>
Co-authored-by: Antonio Bennett <abennett@mabelslabels.com>
Co-authored-by: FORMI <239411042+Richman018@users.noreply.github.com>
Co-authored-by: Miner <miner@example.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 .changeset/sharp-snakes-poke.md               |  5 +++
 .../3-transform/client/visitors/EachBlock.js  |  4 --
 .../src/internal/client/dom/blocks/each.js    | 37 +++++++++++++++++++
 packages/svelte/src/internal/client/index.js  |  2 +-
 .../svelte/src/internal/client/validate.js    | 34 -----------------
 .../samples/keyed-each-unique-2/_config.js    | 12 ++++++
 .../samples/keyed-each-unique-2/main.svelte   |  8 ++++
 .../samples/keyed-each-unique-3/_config.js    |  5 +++
 .../samples/keyed-each-unique-3/main.svelte   |  7 ++++
 .../samples/keyed-each-unique/_config.js      | 12 ++++++
 .../samples/keyed-each-unique/main.svelte     |  8 ++++
 11 files changed, 95 insertions(+), 39 deletions(-)
 create mode 100644 .changeset/sharp-snakes-poke.md
 create mode 100644 packages/svelte/tests/runtime-production/samples/keyed-each-unique-2/_config.js
 create mode 100644 packages/svelte/tests/runtime-production/samples/keyed-each-unique-2/main.svelte
 create mode 100644 packages/svelte/tests/runtime-production/samples/keyed-each-unique-3/_config.js
 create mode 100644 packages/svelte/tests/runtime-production/samples/keyed-each-unique-3/main.svelte
 create mode 100644 packages/svelte/tests/runtime-production/samples/keyed-each-unique/_config.js
 create mode 100644 packages/svelte/tests/runtime-production/samples/keyed-each-unique/main.svelte

diff --git a/.changeset/sharp-snakes-poke.md b/.changeset/sharp-snakes-poke.md
new file mode 100644
index 0000000000..7f7f8aa7b2
--- /dev/null
+++ b/.changeset/sharp-snakes-poke.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: emit `each_key_duplicate` error in production
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
index 1dbc34fdc3..b2724fa90f 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/EachBlock.js
@@ -338,10 +338,6 @@ export function EachBlock(node, context) {
 
 	const statements = [add_svelte_meta(b.call('$.each', ...args), node, 'each')];
 
-	if (dev && node.metadata.keyed) {
-		statements.unshift(b.stmt(b.call('$.validate_each_keys', thunk, key_function)));
-	}
-
 	if (node.metadata.expression.is_async()) {
 		context.state.init.push(
 			b.stmt(
diff --git a/packages/svelte/src/internal/client/dom/blocks/each.js b/packages/svelte/src/internal/client/dom/blocks/each.js
index 6eaeac0f38..25f7cf91eb 100644
--- a/packages/svelte/src/internal/client/dom/blocks/each.js
+++ b/packages/svelte/src/internal/client/dom/blocks/each.js
@@ -40,6 +40,7 @@ import { get } from '../../runtime.js';
 import { DEV } from 'esm-env';
 import { derived_safe_equal } from '../../reactivity/deriveds.js';
 import { current_batch } from '../../reactivity/batch.js';
+import * as e from '../../errors.js';
 
 // When making substantive changes to this file, validate them with the each block stress test:
 // https://svelte.dev/playground/1972b2cf46564476ad8c8c6405b23b7b
@@ -290,6 +291,15 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 			}
 		}
 
+		if (length > keys.size) {
+			if (DEV) {
+				validate_each_keys(array, get_key);
+			} else {
+				// in prod, the additional information isn't printed, so don't bother computing it
+				e.each_key_duplicate('', '', '');
+			}
+		}
+
 		// remove excess nodes
 		if (hydrating && length > 0) {
 			set_hydrate_node(skip_nodes());
@@ -676,3 +686,30 @@ function link(state, prev, next) {
 		next.prev = prev;
 	}
 }
+
+/**
+ * @param {Array<any>} array
+ * @param {(item: any, index: number) => string} key_fn
+ * @returns {void}
+ */
+function validate_each_keys(array, key_fn) {
+	const keys = new Map();
+	const length = array.length;
+
+	for (let i = 0; i < length; i++) {
+		const key = key_fn(array[i], i);
+
+		if (keys.has(key)) {
+			const a = String(keys.get(key));
+			const b = String(i);
+
+			/** @type {string | null} */
+			let k = String(key);
+			if (k.startsWith('[object ')) k = null;
+
+			e.each_key_duplicate(a, b, k);
+		}
+
+		keys.set(key, i);
+	}
+}
diff --git a/packages/svelte/src/internal/client/index.js b/packages/svelte/src/internal/client/index.js
index 1d9f7dfff7..7fcaf77dc5 100644
--- a/packages/svelte/src/internal/client/index.js
+++ b/packages/svelte/src/internal/client/index.js
@@ -158,7 +158,7 @@ export {
 	deep_read_state,
 	active_effect
 } from './runtime.js';
-export { validate_binding, validate_each_keys } from './validate.js';
+export { validate_binding } from './validate.js';
 export { raf } from './timing.js';
 export { proxy } from './proxy.js';
 export { create_custom_element } from './dom/elements/custom-element.js';
diff --git a/packages/svelte/src/internal/client/validate.js b/packages/svelte/src/internal/client/validate.js
index 48a44db304..a169225f1e 100644
--- a/packages/svelte/src/internal/client/validate.js
+++ b/packages/svelte/src/internal/client/validate.js
@@ -1,45 +1,11 @@
 /** @import { Blocker } from '#client' */
 import { dev_current_component_function } from './context.js';
-import { is_array } from '../shared/utils.js';
-import * as e from './errors.js';
 import { FILENAME } from '../../constants.js';
 import { render_effect } from './reactivity/effects.js';
 import * as w from './warnings.js';
 import { capture_store_binding } from './reactivity/store.js';
 import { run_after_blockers } from './reactivity/async.js';
 
-/**
- * @param {() => any} collection
- * @param {(item: any, index: number) => string} key_fn
- * @returns {void}
- */
-export function validate_each_keys(collection, key_fn) {
-	render_effect(() => {
-		const keys = new Map();
-		const maybe_array = collection();
-		const array = is_array(maybe_array)
-			? maybe_array
-			: maybe_array == null
-				? []
-				: Array.from(maybe_array);
-		const length = array.length;
-		for (let i = 0; i < length; i++) {
-			const key = key_fn(array[i], i);
-			if (keys.has(key)) {
-				const a = String(keys.get(key));
-				const b = String(i);
-
-				/** @type {string | null} */
-				let k = String(key);
-				if (k.startsWith('[object ')) k = null;
-
-				e.each_key_duplicate(a, b, k);
-			}
-			keys.set(key, i);
-		}
-	});
-}
-
 /**
  * @param {string} binding
  * @param {Blocker[]} blockers
diff --git a/packages/svelte/tests/runtime-production/samples/keyed-each-unique-2/_config.js b/packages/svelte/tests/runtime-production/samples/keyed-each-unique-2/_config.js
new file mode 100644
index 0000000000..bc945876ea
--- /dev/null
+++ b/packages/svelte/tests/runtime-production/samples/keyed-each-unique-2/_config.js
@@ -0,0 +1,12 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	test({ assert, target }) {
+		let button = target.querySelector('button');
+
+		button?.click();
+
+		assert.throws(flushSync, 'https://svelte.dev/e/each_key_duplicate');
+	}
+});
diff --git a/packages/svelte/tests/runtime-production/samples/keyed-each-unique-2/main.svelte b/packages/svelte/tests/runtime-production/samples/keyed-each-unique-2/main.svelte
new file mode 100644
index 0000000000..f8ba50d866
--- /dev/null
+++ b/packages/svelte/tests/runtime-production/samples/keyed-each-unique-2/main.svelte
@@ -0,0 +1,8 @@
+<script>
+	let data = $state([1, 2, 3]);
+</script>
+
+<button onclick={() => data = [1, 1, 1]}>add</button>
+{#each data as d (d)}
+	{d}
+{/each}
diff --git a/packages/svelte/tests/runtime-production/samples/keyed-each-unique-3/_config.js b/packages/svelte/tests/runtime-production/samples/keyed-each-unique-3/_config.js
new file mode 100644
index 0000000000..7e1840200a
--- /dev/null
+++ b/packages/svelte/tests/runtime-production/samples/keyed-each-unique-3/_config.js
@@ -0,0 +1,5 @@
+import { test } from '../../test';
+
+export default test({
+	error: 'each_key_duplicate'
+});
diff --git a/packages/svelte/tests/runtime-production/samples/keyed-each-unique-3/main.svelte b/packages/svelte/tests/runtime-production/samples/keyed-each-unique-3/main.svelte
new file mode 100644
index 0000000000..a05781bcb9
--- /dev/null
+++ b/packages/svelte/tests/runtime-production/samples/keyed-each-unique-3/main.svelte
@@ -0,0 +1,7 @@
+<script>
+	let data = [1, 1, 1];
+</script>
+
+{#each data as d (d)}
+	{d}
+{/each}
diff --git a/packages/svelte/tests/runtime-production/samples/keyed-each-unique/_config.js b/packages/svelte/tests/runtime-production/samples/keyed-each-unique/_config.js
new file mode 100644
index 0000000000..bc945876ea
--- /dev/null
+++ b/packages/svelte/tests/runtime-production/samples/keyed-each-unique/_config.js
@@ -0,0 +1,12 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	test({ assert, target }) {
+		let button = target.querySelector('button');
+
+		button?.click();
+
+		assert.throws(flushSync, 'https://svelte.dev/e/each_key_duplicate');
+	}
+});
diff --git a/packages/svelte/tests/runtime-production/samples/keyed-each-unique/main.svelte b/packages/svelte/tests/runtime-production/samples/keyed-each-unique/main.svelte
new file mode 100644
index 0000000000..3d52179372
--- /dev/null
+++ b/packages/svelte/tests/runtime-production/samples/keyed-each-unique/main.svelte
@@ -0,0 +1,8 @@
+<script>
+	let data = $state([1, 2, 3, 4, 5]);
+</script>
+
+<button onclick={() => data = [1, 1, 3, 1]}>add</button>
+{#each data as d (d)}
+	{d}
+{/each}