Apply suggestions from code review

Author: Rich-Harris

packages/svelte/src/compiler/phases/3-transform/client/visitors/AssignmentExpression.js

@@ -75,8 +75,7 @@ function build_assignment(operator, left, right, context) {
 				context.state.in_constructor ? '$.simple_set' : '$.set',
 				left,
 				value,
-				needs_proxy && b.true,
-				dev && needs_proxy && b.true
+				needs_proxy && b.true
 			);
 		}
 	}

packages/svelte/src/compiler/phases/3-transform/client/visitors/ClassBody.js

@@ -159,11 +159,7 @@ export function ClassBody(node, context) {
 								'set',
 								definition.key,
 								[value],
-								[
-									b.stmt(
-										b.call('$.set', member, value, field.kind === 'state' && b.true, dev && b.true)
-									)
-								]
+								[b.stmt(b.call('$.set', member, value, field.kind === 'state' && b.true))]
 							)
 						);
 					}

packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/declarations.js

@@ -26,7 +26,7 @@ export function add_state_transformers(context) {
 			context.state.transform[name] = {
 				read: binding.declaration_kind === 'var' ? (node) => b.call('$.safe_get', node) : get_value,
 				assign: (node, value, proxy = false) => {
-					let call = b.call('$.set', node, value, proxy && b.true, dev && proxy && b.true);
+					let call = b.call('$.set', node, value, proxy && b.true);
 
 					if (context.state.scope.get(`$${node.name}`)?.kind === 'store_sub') {
 						call = b.call('$.store_unsub', call, b.literal(`$${node.name}`), b.id('$$stores'));

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

@@ -183,10 +183,9 @@ export function mutate(source, value) {
  * @param {Source<V>} source
  * @param {V} value
  * @param {boolean} [should_proxy]
- * @param {boolean} [needs_previous]
  * @returns {V}
  */
-export function set(source, value, should_proxy = false, needs_previous = false) {
+export function set(source, value, should_proxy = false) {
 	if (
 		active_reaction !== null &&
 		!untracking &&
@@ -200,7 +199,7 @@ export function set(source, value, should_proxy = false, needs_previous = false)
 	}
 
 	let new_value = should_proxy
-		? needs_previous
+		? DEV
 			? proxy(value, source.o, null, source)
 			: proxy(value, source.o)
 		: value;
@@ -213,12 +212,11 @@ export function set(source, value, should_proxy = false, needs_previous = false)
  * @param {Source<V>} source
  * @param {V} value
  * @param {boolean} [should_proxy]
- * @param {boolean} [needs_previous]
  * @returns {V}
  */
-export function simple_set(source, value, should_proxy = false, needs_previous = false) {
+export function simple_set(source, value, should_proxy = false) {
 	let new_value = should_proxy
-		? needs_previous
+		? DEV
 			? proxy(value, source.o, null, source)
 			: proxy(value, source.o)
 		: value;