fix: don't clone non-proxies in `$inspect`

.changeset/itchy-games-guess.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: don't clone non-proxies in `$inspect`

packages/svelte/src/internal/client/dev/inspect.js

@@ -26,7 +26,7 @@ export function inspect(get_value, inspector = console.log) {
 			return;
 		}
 
-		var snap = snapshot(value, true);
+		var snap = snapshot(value, true, true);
 		untrack(() => {
 			inspector(initial ? 'init' : 'update', ...snap);
 		});

packages/svelte/src/internal/shared/clone.js

@@ -15,9 +15,10 @@ const empty = [];
  * @template T
  * @param {T} value
  * @param {boolean} [skip_warning]
+ * @param {boolean} [only_deproxy]
  * @returns {Snapshot<T>}
  */
-export function snapshot(value, skip_warning = false) {
+export function snapshot(value, skip_warning = false, only_deproxy = false) {
 	if (DEV && !skip_warning) {
 		/** @type {string[]} */
 		const paths = [];
@@ -40,7 +41,7 @@ export function snapshot(value, skip_warning = false) {
 		return copy;
 	}
 
-	return clone(value, new Map(), '', empty);
+	return clone(value, new Map(), '', empty, null, only_deproxy);
 }
 
 /**
@@ -49,16 +50,19 @@ export function snapshot(value, skip_warning = false) {
  * @param {Map<T, Snapshot<T>>} cloned
  * @param {string} path
  * @param {string[]} paths
- * @param {null | T} original The original value, if `value` was produced from a `toJSON` call
+ * @param {null | T} [original] The original value, if `value` was produced from a `toJSON` call
+ * @param {boolean} [only_deproxy] Don't clone objects that aren't proxies
  * @returns {Snapshot<T>}
  */
-function clone(value, cloned, path, paths, original = null) {
+function clone(value, cloned, path, paths, original = null, only_deproxy = false) {
 	if (typeof value === 'object' && value !== null) {
 		var unwrapped = cloned.get(value);
 		if (unwrapped !== undefined) return unwrapped;
 
-		if (value instanceof Map) return /** @type {Snapshot<T>} */ (new Map(value));
-		if (value instanceof Set) return /** @type {Snapshot<T>} */ (new Set(value));
+		if (value instanceof Map)
+			return /** @type {Snapshot<T>} */ (only_deproxy ? value : new Map(value));
+		if (value instanceof Set)
+			return /** @type {Snapshot<T>} */ (only_deproxy ? value : new Set(value));
 
 		if (is_array(value)) {
 			var copy = /** @type {Snapshot<any>} */ (Array(value.length));
@@ -71,7 +75,7 @@ function clone(value, cloned, path, paths, original = null) {
 			for (var i = 0; i < value.length; i += 1) {
 				var element = value[i];
 				if (i in value) {
-					copy[i] = clone(element, cloned, DEV ? `${path}[${i}]` : path, paths);
+					copy[i] = clone(element, cloned, DEV ? `${path}[${i}]` : path, paths, null, only_deproxy);
 				}
 			}
 
@@ -88,26 +92,49 @@ function clone(value, cloned, path, paths, original = null) {
 			}
 
 			for (var key in value) {
-				// @ts-expect-error
-				copy[key] = clone(value[key], cloned, DEV ? `${path}.${key}` : path, paths);
+				copy[key] = clone(
+					// @ts-expect-error
+					value[key],
+					cloned,
+					DEV ? `${path}.${key}` : path,
+					paths,
+					null,
+					only_deproxy
+				);
 			}
 
 			return copy;
 		}
 
 		if (value instanceof Date) {
-			return /** @type {Snapshot<T>} */ (structuredClone(value));
+			if (only_deproxy) {
+				structuredClone(value);
+			} else {
+				return /** @type {Snapshot<T>} */ (structuredClone(value));
+			}
 		}
 
 		if (typeof (/** @type {T & { toJSON?: any } } */ (value).toJSON) === 'function') {
-			return clone(
-				/** @type {T & { toJSON(): any } } */ (value).toJSON(),
-				cloned,
-				DEV ? `${path}.toJSON()` : path,
-				paths,
-				// Associate the instance with the toJSON clone
-				value
-			);
+			if (!only_deproxy) {
+				return clone(
+					/** @type {T & { toJSON(): any } } */ (value).toJSON(),
+					cloned,
+					DEV ? `${path}.toJSON()` : path,
+					paths,
+					// Associate the instance with the toJSON clone
+					value
+				);
+			} else {
+				// we still want to read each property
+				clone(
+					/** @type {T & { toJSON(): any } } */ (value).toJSON(),
+					cloned,
+					DEV ? `${path}.toJSON()` : path,
+					paths,
+					// Associate the instance with the toJSON clone
+					value
+				);
+			}
 		}
 	}
 
@@ -116,6 +143,13 @@ function clone(value, cloned, path, paths, original = null) {
 		return /** @type {Snapshot<T>} */ (value);
 	}
 
+	if (only_deproxy) {
+		try {
+			structuredClone(value);
+		} catch {}
+		return /** @type {Snapshot<T>} */ (value);
+	}
+
 	try {
 		return /** @type {Snapshot<T>} */ (structuredClone(value));
 	} catch (e) {