From fa5d3a9002106c9abc15f25dfafef1e24ca4ae7a Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Mon, 12 Aug 2024 16:26:32 +0100
Subject: [PATCH] fix: ensure inspect effects are skipped from effect parent
 logic (#12810)

---
 .changeset/stupid-cars-behave.md                   |  5 +++++
 .../src/internal/client/reactivity/effects.js      | 14 +++++++++++---
 .../samples/inspect-nested-effect/_config.js       | 11 +++++++++++
 .../samples/inspect-nested-effect/main.svelte      | 12 ++++++++++++
 4 files changed, 39 insertions(+), 3 deletions(-)
 create mode 100644 .changeset/stupid-cars-behave.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/inspect-nested-effect/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/inspect-nested-effect/main.svelte

diff --git a/.changeset/stupid-cars-behave.md b/.changeset/stupid-cars-behave.md
new file mode 100644
index 0000000000..9612cb3a86
--- /dev/null
+++ b/.changeset/stupid-cars-behave.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure inspect effects are skipped from effect parent logic
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index 9fd238c866..d05243bb14 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/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
diff --git a/packages/svelte/tests/runtime-runes/samples/inspect-nested-effect/_config.js b/packages/svelte/tests/runtime-runes/samples/inspect-nested-effect/_config.js
new file mode 100644
index 0000000000..82429e5e36
--- /dev/null
+++ b/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]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/inspect-nested-effect/main.svelte b/packages/svelte/tests/runtime-runes/samples/inspect-nested-effect/main.svelte
new file mode 100644
index 0000000000..3693e4f6d5
--- /dev/null
+++ b/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>
+