From 657ec89caa93d39d2cf8d8cdbe27b0041615409f Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sat, 25 Oct 2025 14:12:22 -0400
Subject: [PATCH] fix: ignore fork `discard()` after `commit()` (#17034)

* fix: ignore fork `discard()` after `commit()`

* fix message
---
 .changeset/twenty-onions-attack.md            |  5 +++++
 .../98-reference/.generated/client-errors.md  |  2 +-
 .../svelte/messages/client-errors/errors.md   |  2 +-
 packages/svelte/src/internal/client/errors.js |  4 ++--
 .../src/internal/client/reactivity/batch.js   | 22 +++++++++++++------
 5 files changed, 24 insertions(+), 11 deletions(-)
 create mode 100644 .changeset/twenty-onions-attack.md

diff --git a/.changeset/twenty-onions-attack.md b/.changeset/twenty-onions-attack.md
new file mode 100644
index 0000000000..c23c8b590b
--- /dev/null
+++ b/.changeset/twenty-onions-attack.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ignore fork `discard()` after `commit()`
diff --git a/documentation/docs/98-reference/.generated/client-errors.md b/documentation/docs/98-reference/.generated/client-errors.md
index 74a0674dba..3f1cb8f76b 100644
--- a/documentation/docs/98-reference/.generated/client-errors.md
+++ b/documentation/docs/98-reference/.generated/client-errors.md
@@ -149,7 +149,7 @@ This restriction only applies when using the `experimental.async` option, which
 ### fork_discarded
 
 ```
-Cannot commit a fork that was already committed or discarded
+Cannot commit a fork that was already discarded
 ```
 
 ### fork_timing
diff --git a/packages/svelte/messages/client-errors/errors.md b/packages/svelte/messages/client-errors/errors.md
index b5fe51539d..ae7d811b2e 100644
--- a/packages/svelte/messages/client-errors/errors.md
+++ b/packages/svelte/messages/client-errors/errors.md
@@ -114,7 +114,7 @@ This restriction only applies when using the `experimental.async` option, which
 
 ## fork_discarded
 
-> Cannot commit a fork that was already committed or discarded
+> Cannot commit a fork that was already discarded
 
 ## fork_timing
 
diff --git a/packages/svelte/src/internal/client/errors.js b/packages/svelte/src/internal/client/errors.js
index 2a433ed8f9..8a5fde4f3b 100644
--- a/packages/svelte/src/internal/client/errors.js
+++ b/packages/svelte/src/internal/client/errors.js
@@ -262,12 +262,12 @@ export function flush_sync_in_effect() {
 }
 
 /**
- * Cannot commit a fork that was already committed or discarded
+ * Cannot commit a fork that was already discarded
  * @returns {never}
  */
 export function fork_discarded() {
 	if (DEV) {
-		const error = new Error(`fork_discarded\nCannot commit a fork that was already committed or discarded\nhttps://svelte.dev/e/fork_discarded`);
+		const error = new Error(`fork_discarded\nCannot commit a fork that was already discarded\nhttps://svelte.dev/e/fork_discarded`);
 
 		error.name = 'Svelte error';
 
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index fdeb111a4d..ab83050cd0 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -913,28 +913,36 @@ export function fork(fn) {
 		e.fork_timing();
 	}
 
-	const batch = Batch.ensure();
+	var batch = Batch.ensure();
 	batch.is_fork = true;
 
-	const settled = batch.settled();
+	var committed = false;
+	var settled = batch.settled();
 
 	flushSync(fn);
 
 	// revert state changes
-	for (const [source, value] of batch.previous) {
+	for (var [source, value] of batch.previous) {
 		source.v = value;
 	}
 
 	return {
 		commit: async () => {
+			if (committed) {
+				await settled;
+				return;
+			}
+
 			if (!batches.has(batch)) {
 				e.fork_discarded();
 			}
 
+			committed = true;
+
 			batch.is_fork = false;
 
 			// apply changes
-			for (const [source, value] of batch.current) {
+			for (var [source, value] of batch.current) {
 				source.v = value;
 			}
 
@@ -945,9 +953,9 @@ export function fork(fn) {
 			// TODO maybe there's a better implementation?
 			flushSync(() => {
 				/** @type {Set<Effect>} */
-				const eager_effects = new Set();
+				var eager_effects = new Set();
 
-				for (const source of batch.current.keys()) {
+				for (var source of batch.current.keys()) {
 					mark_eager_effects(source, eager_effects);
 				}
 
@@ -959,7 +967,7 @@ export function fork(fn) {
 			await settled;
 		},
 		discard: () => {
-			if (batches.has(batch)) {
+			if (!committed && batches.has(batch)) {
 				batches.delete(batch);
 				batch.discard();
 			}