From a543559acfb21ecc509873790158ba16db4089fd Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Thu, 14 Aug 2025 13:36:29 -0700
Subject: [PATCH] fix: avoid recursion error when tagging circular references
 (#16622)

* fix: avoid recursion error when tagging circular references

* try suggestion

* add some logging

* make logging clearer

* more

* try this

* add test

* tweak

* fix?

* fix??
---
 .changeset/six-shirts-scream.md               |  5 ++++
 packages/svelte/src/internal/client/proxy.js  | 11 +++++---
 .../_config.js                                | 26 +++++++++++++++++++
 .../main.svelte                               | 10 +++++++
 4 files changed, 48 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/six-shirts-scream.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/inspect-trace-circular-reference/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/inspect-trace-circular-reference/main.svelte

diff --git a/.changeset/six-shirts-scream.md b/.changeset/six-shirts-scream.md
new file mode 100644
index 0000000000..ac4d183474
--- /dev/null
+++ b/.changeset/six-shirts-scream.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: avoid recursion error when tagging circular references
diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index 3ae4b87ed5..dae3791eb0 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -93,9 +93,11 @@ export function proxy(value) {
 
 	/** Used in dev for $inspect.trace() */
 	var path = '';
-
+	let updating = false;
 	/** @param {string} new_path */
 	function update_path(new_path) {
+		if (updating) return;
+		updating = true;
 		path = new_path;
 
 		tag(version, `${path} version`);
@@ -104,6 +106,7 @@ export function proxy(value) {
 		for (const [prop, source] of sources) {
 			tag(source, get_label(path, prop));
 		}
+		updating = false;
 	}
 
 	return new Proxy(/** @type {any} */ (value), {
@@ -284,13 +287,13 @@ export function proxy(value) {
 			if (s === undefined) {
 				if (!has || get_descriptor(target, prop)?.writable) {
 					s = with_parent(() => source(undefined, stack));
-					set(s, proxy(value));
-
-					sources.set(prop, s);
 
 					if (DEV) {
 						tag(s, get_label(path, prop));
 					}
+					set(s, proxy(value));
+
+					sources.set(prop, s);
 				}
 			} else {
 				has = s.v !== UNINITIALIZED;
diff --git a/packages/svelte/tests/runtime-runes/samples/inspect-trace-circular-reference/_config.js b/packages/svelte/tests/runtime-runes/samples/inspect-trace-circular-reference/_config.js
new file mode 100644
index 0000000000..ca81c7854a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/inspect-trace-circular-reference/_config.js
@@ -0,0 +1,26 @@
+import { test } from '../../test';
+import { normalise_trace_logs } from '../../../helpers.js';
+
+export default test({
+	compileOptions: {
+		dev: true
+	},
+
+	test({ assert, logs }) {
+		const files = { id: 1, items: [{ id: 2, items: [{ id: 3 }, { id: 4 }] }] };
+		// @ts-expect-error
+		files.items[0].parent = files;
+		assert.deepEqual(normalise_trace_logs(logs), [
+			{ log: 'test (main.svelte:5:4)' },
+			{ log: '$state', highlighted: true },
+			{ log: 'filesState.files', highlighted: false },
+			{ log: files },
+			{ log: '$state', highlighted: true },
+			{ log: 'filesState.files.items[0].parent.items', highlighted: false },
+			{ log: files.items },
+			{ log: '$state', highlighted: true },
+			{ log: 'filesState.files.items[0].parent.items[0]', highlighted: false },
+			{ log: files.items[0] }
+		]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/inspect-trace-circular-reference/main.svelte b/packages/svelte/tests/runtime-runes/samples/inspect-trace-circular-reference/main.svelte
new file mode 100644
index 0000000000..7640d48f77
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/inspect-trace-circular-reference/main.svelte
@@ -0,0 +1,10 @@
+<script>
+    const filesState = $state({ files: {} });
+    let nodes = { id: 1, items: [{ id: 2, items: [{ id: 3 }, { id: 4 }] }] };
+    filesState.files = nodes;
+    function test() {
+        $inspect.trace();
+        filesState.files.items[0].parent = filesState.files;
+    }
+    $effect(test);
+</script>
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