fix: ensure inspect effects are skipped from effect parent logic (#12810)

.changeset/stupid-cars-behave.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure inspect effects are skipped from effect parent logic

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

@@ -81,6 +81,14 @@ export function push_effect(effect, parent_effect) {
  */
 function create_effect(type, fn, sync, push = true) {
 	var is_root = (type & ROOT_EFFECT) !== 0;
+	var parent_effect = current_effect;
+
+	if (DEV) {
+		// Ensure the parent is never an inspect effect
+		while (parent_effect !== null && (parent_effect.f & INSPECT_EFFECT) !== 0) {
+			parent_effect = parent_effect.parent;
+		}
+	}
 
 	/** @type {Effect} */
 	var effect = {
@@ -92,7 +100,7 @@ function create_effect(type, fn, sync, push = true) {
 		fn,
 		last: null,
 		next: null,
-		parent: is_root ? null : current_effect,
+		parent: is_root ? null : parent_effect,
 		prev: null,
 		teardown: null,
 		transitions: null,
@@ -130,8 +138,8 @@ function create_effect(type, fn, sync, push = true) {
 		effect.teardown === null;
 
 	if (!inert && !is_root && push) {
-		if (current_effect !== null) {
-			push_effect(effect, current_effect);
+		if (parent_effect !== null) {
+			push_effect(effect, parent_effect);
 		}
 
 		// if we're in a derived, add the effect there too

packages/svelte/tests/runtime-runes/samples/inspect-nested-effect/_config.js

@@ -0,0 +1,11 @@
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true
+	},
+
+	async test({ assert, logs }) {
+		assert.deepEqual(logs, ['init', 0, 'update', 1]);
+	}
+});

packages/svelte/tests/runtime-runes/samples/inspect-nested-effect/main.svelte

@@ -0,0 +1,12 @@
+<script>
+	let a = $state(0);
+	let b = $derived.by(() => {
+		$effect(() => {
+			a = 1;
+		})
+		return a;
+	})
+
+	$inspect(b);
+</script>
+