require users to discard forks

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 (including as a result of a different fork being committed)
+Cannot commit a fork that was already committed or discarded
 ```
 
 ### fork_timing

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 (including as a result of a different fork being committed)
+> Cannot commit a fork that was already committed or discarded
 
 ## fork_timing
 

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

@@ -262,34 +262,34 @@ export function flush_sync_in_effect() {
 }
 
 /**
- * Cannot create a fork inside an effect or when state changes are pending
+ * Cannot commit a fork that was already committed or discarded
  * @returns {never}
  */
-export function fork_timing() {
+export function fork_discarded() {
 	if (DEV) {
-		const error = new Error(`fork_timing\nCannot create a fork inside an effect or when state changes are pending\nhttps://svelte.dev/e/fork_timing`);
+		const error = new Error(`fork_discarded\nCannot commit a fork that was already committed or discarded\nhttps://svelte.dev/e/fork_discarded`);
 
 		error.name = 'Svelte error';
 
 		throw error;
 	} else {
-		throw new Error(`https://svelte.dev/e/fork_timing`);
+		throw new Error(`https://svelte.dev/e/fork_discarded`);
 	}
 }
 
 /**
- * Cannot commit a fork that was already committed or discarded (including as a result of a different fork being committed)
+ * Cannot create a fork inside an effect or when state changes are pending
  * @returns {never}
  */
-export function fork_discarded() {
+export function fork_timing() {
 	if (DEV) {
-		const error = new Error(`fork_discarded\nCannot commit a fork that was already committed or discarded (including as a result of a different fork being committed)\nhttps://svelte.dev/e/fork_discarded`);
+		const error = new Error(`fork_timing\nCannot create a fork inside an effect or when state changes are pending\nhttps://svelte.dev/e/fork_timing`);
 
 		error.name = 'Svelte error';
 
 		throw error;
 	} else {
-		throw new Error(`https://svelte.dev/e/fork_discarded`);
+		throw new Error(`https://svelte.dev/e/fork_timing`);
 	}
 }
 

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

@@ -880,6 +880,9 @@ export function eager(fn) {
  * state changes will be reverted after the fork is initialised, then reapplied
  * if and when the fork is eventually committed.
  *
+ * When it becomes clear that a fork will _not_ be committed (e.g. because the
+ * user navigated elsewhere), it must be discarded to avoid leaking memory.
+ *
  * @param {() => void} fn
  * @returns {{ commit: () => void, discard: () => void }}
  */
@@ -912,11 +915,6 @@ export function fork(fn) {
 
 			batch.is_fork = false;
 
-			// delete all other forks
-			for (const b of batches) {
-				if (b.is_fork) batches.delete(b);
-			}
-
 			// apply changes
 			for (const [source, value] of batch.current) {
 				source.v = value;

packages/svelte/types/index.d.ts

@@ -460,6 +460,9 @@ declare module 'svelte' {
 	 * state changes will be reverted after the fork is initialised, then reapplied
 	 * if and when the fork is eventually committed.
 	 *
+	 * When it becomes clear that a fork will _not_ be committed (e.g. because the
+	 * user navigated elsewhere), it must be discarded to avoid leaking memory.
+	 *
 	 * */
 	export function fork(fn: () => void): {
 		commit: () => void;