From 5f218b5f3d98a4b9333db595993c93c59815a59e Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Fri, 31 May 2024 16:17:46 +0100
Subject: [PATCH] chore: improve $state.frozen performance in prod (#11852)

* chore: improve $state.frozen performance in prod

* lint

* feedback
---
 .changeset/silver-sheep-knock.md              |  5 ++++
 .../svelte/src/internal/client/constants.js   |  1 +
 packages/svelte/src/internal/client/proxy.js  | 15 ++++++----
 .../svelte/src/internal/client/runtime.js     | 30 ++++++++++++++-----
 4 files changed, 38 insertions(+), 13 deletions(-)
 create mode 100644 .changeset/silver-sheep-knock.md

diff --git a/.changeset/silver-sheep-knock.md b/.changeset/silver-sheep-knock.md
new file mode 100644
index 0000000000..5c1ab0a910
--- /dev/null
+++ b/.changeset/silver-sheep-knock.md
@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+chore: improve $state.frozen performance in prod
diff --git a/packages/svelte/src/internal/client/constants.js b/packages/svelte/src/internal/client/constants.js
index 543f812e79..0d691cfd96 100644
--- a/packages/svelte/src/internal/client/constants.js
+++ b/packages/svelte/src/internal/client/constants.js
@@ -18,4 +18,5 @@ export const EFFECT_TRANSPARENT = 1 << 15;
 export const LEGACY_DERIVED_PROP = 1 << 16;
 
 export const STATE_SYMBOL = Symbol('$state');
+export const STATE_FROZEN_SYMBOL = Symbol('$state.frozen');
 export const LOADING_ATTR_SYMBOL = Symbol('');
diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index 31a22600b6..53ce093dc3 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -18,20 +18,25 @@ import {
 } from './utils.js';
 import { check_ownership, widen_ownership } from './dev/ownership.js';
 import { mutable_source, source, set } from './reactivity/sources.js';
-import { STATE_SYMBOL } from './constants.js';
+import { STATE_FROZEN_SYMBOL, STATE_SYMBOL } from './constants.js';
 import { UNINITIALIZED } from '../../constants.js';
 import * as e from './errors.js';
 
 /**
  * @template T
- * @param {T} value
+ * @param {T} initial_value
  * @param {boolean} [immutable]
  * @param {import('#client').ProxyMetadata | null} [parent]
  * @param {import('#client').Source<T>} [prev] dev mode only
  * @returns {import('#client').ProxyStateObject<T> | T}
  */
-export function proxy(value, immutable = true, parent = null, prev) {
-	if (typeof value === 'object' && value != null && !is_frozen(value)) {
+export function proxy(initial_value, immutable = true, parent = null, prev) {
+	if (typeof initial_value === 'object' && initial_value != null) {
+		let value = initial_value;
+		// If the object is frozen then snapshot the value
+		if (is_frozen(value) || STATE_FROZEN_SYMBOL in value) {
+			value = snapshot(value);
+		}
 		// If we have an existing proxy, return it...
 		if (STATE_SYMBOL in value) {
 			const metadata = /** @type {import('#client').ProxyMetadata<T>} */ (value[STATE_SYMBOL]);
@@ -94,7 +99,7 @@ export function proxy(value, immutable = true, parent = null, prev) {
 		}
 	}
 
-	return value;
+	return initial_value;
 }
 
 /**
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 8fe016532d..545d3f6561 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -1,5 +1,11 @@
 import { DEV } from 'esm-env';
-import { get_descriptors, get_prototype_of, is_frozen, object_freeze } from './utils.js';
+import {
+	define_property,
+	get_descriptors,
+	get_prototype_of,
+	is_frozen,
+	object_freeze
+} from './utils.js';
 import { snapshot } from './proxy.js';
 import { destroy_effect, effect, execute_effect_teardown } from './reactivity/effects.js';
 import {
@@ -17,7 +23,8 @@ import {
 	BLOCK_EFFECT,
 	ROOT_EFFECT,
 	LEGACY_DERIVED_PROP,
-	DISCONNECTED
+	DISCONNECTED,
+	STATE_FROZEN_SYMBOL
 } from './constants.js';
 import { flush_tasks } from './dom/task.js';
 import { add_owner } from './dev/ownership.js';
@@ -1353,19 +1360,26 @@ if (DEV) {
 }
 
 /**
- * Expects a value that was wrapped with `freeze` and makes it frozen.
+ * Expects a value that was wrapped with `freeze` and makes it frozen in DEV.
  * @template T
  * @param {T} value
  * @returns {Readonly<T>}
  */
 export function freeze(value) {
-	if (typeof value === 'object' && value != null && !is_frozen(value)) {
+	if (typeof value === 'object' && value != null && !(STATE_FROZEN_SYMBOL in value)) {
 		// If the object is already proxified, then snapshot the value
-		if (STATE_SYMBOL in value) {
-			return object_freeze(snapshot(value));
+		if (STATE_SYMBOL in value || is_frozen(value)) {
+			value = snapshot(value);
+		}
+		define_property(value, STATE_FROZEN_SYMBOL, {
+			value: true,
+			writable: true,
+			enumerable: false
+		});
+		// Freeze the object in DEV
+		if (DEV) {
+			object_freeze(value);
 		}
-		// Otherwise freeze the object
-		object_freeze(value);
 	}
 	return value;
 }