add effect_pending_outside_reaction error

documentation/docs/98-reference/.generated/client-errors.md

@@ -80,6 +80,12 @@ Effect cannot be created inside a `$derived` value that was not itself created i
 `%rune%` can only be used inside an effect (e.g. during component initialisation)
 ```
 
+### effect_pending_outside_reaction
+
+```
+`$effect.pending()` can only be called inside an effect or derived
+```
+
 ### effect_update_depth_exceeded
 
 ```

packages/svelte/messages/client-errors/errors.md

@@ -54,6 +54,10 @@ See the [migration guide](/docs/svelte/v5-migration-guide#Components-are-no-long
 
 > `%rune%` can only be used inside an effect (e.g. during component initialisation)
 
+## effect_pending_outside_reaction
+
+> `$effect.pending()` can only be called inside an effect or derived
+
 ## effect_update_depth_exceeded
 
 > Maximum update depth exceeded. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops

packages/svelte/scripts/process-messages/templates/client-errors.js

@@ -1,4 +1,5 @@
 import { DEV } from 'esm-env';
+export * from '../shared/errors.js';
 
 /**
  * MESSAGE

packages/svelte/scripts/process-messages/templates/server-errors.js

@@ -1,3 +1,5 @@
+export * from '../shared/errors.js';
+
 /**
  * MESSAGE
  * @param {string} PARAMETER

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

@@ -20,7 +20,7 @@ import {
 } from '../hydration.js';
 import { get_next_sibling } from '../operations.js';
 import { queue_micro_task } from '../task.js';
-import * as e from '../../../shared/errors.js';
+import * as e from '../../errors.js';
 import { DEV } from 'esm-env';
 import { from_async_derived, set_from_async_derived } from '../../reactivity/deriveds.js';
 import { Batch } from '../../reactivity/batch.js';
@@ -454,8 +454,11 @@ function exit() {
 }
 
 export function pending() {
-	// TODO throw helpful error if called outside an effect
-	const boundary = /** @type {Effect} */ (active_effect).b;
+	if (active_effect === null) {
+		e.effect_pending_outside_reaction();
+	}
+
+	var boundary = active_effect.b;
 
 	if (boundary === null) {
 		return 0; // TODO eventually we will need this to be global

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

@@ -2,6 +2,8 @@
 
 import { DEV } from 'esm-env';
 
+export *  from '../shared/errors.js';
+
 /**
  * Cannot create a `$derived(...)` with an `await` expression outside of an effect tree
  * @returns {never}
@@ -195,6 +197,22 @@ export function effect_orphan(rune) {
 	}
 }
 
+/**
+ * `$effect.pending()` can only be called inside an effect or derived
+ * @returns {never}
+ */
+export function effect_pending_outside_reaction() {
+	if (DEV) {
+		const error = new Error(`effect_pending_outside_reaction\n\`$effect.pending()\` can only be called inside an effect or derived\nhttps://svelte.dev/e/effect_pending_outside_reaction`);
+
+		error.name = 'Svelte error';
+
+		throw error;
+	} else {
+		throw new Error(`https://svelte.dev/e/effect_pending_outside_reaction`);
+	}
+}
+
 /**
  * Maximum update depth exceeded. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops
  * @returns {never}

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

@@ -1,6 +1,6 @@
 /* This file is generated by scripts/process-messages/index.js. Do not edit! */
 
-
+export *  from '../shared/errors.js';
 
 /**
  * `%name%(...)` is not available on the server