fix: correctly serialize object assignment expressions

fixes #12174
#12109 didn't take into account actual object assignments and couldn't differentiate them from our "fake" assignments, this fixes that

.changeset/eleven-avocados-walk.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: correctly serialize object assignment expressions

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

@@ -120,7 +120,7 @@ export function serialize_get_binding(node, state) {
  * @param {import('estree').AssignmentExpression} node
  * @param {import('zimmerframe').Context<import('#compiler').SvelteNode, State>} context
  * @param {() => any} fallback
- * @param {boolean} prefix
+ * @param {boolean | null} [prefix] - If the assignment is a transformed update expression, set this. Else `null`
  * @param {{skip_proxy_and_freeze?: boolean}} [options]
  * @returns {import('estree').Expression}
  */
@@ -419,6 +419,7 @@ export function serialize_set_binding(node, context, fallback, prefix, options)
  }
  } else if (
  node.right.type === 'Literal' &&
+ prefix != null &&
  (node.operator === '+=' || node.operator === '-=')
  ) {
  return b.update(

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

@@ -32,7 +32,7 @@ export const global_visitors = {
  next();
  },
  AssignmentExpression(node, context) {
- return serialize_set_binding(node, context, context.next, false);
+ return serialize_set_binding(node, context, context.next);
  },
  UpdateExpression(node, context) {
  const { state, next, visit } = context;

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

@@ -791,9 +791,7 @@ function serialize_inline_component(node, component_name, context) {
  const assignment = b.assignment('=', attribute.expression, b.id('$$value'));
  push_prop(
  b.set(attribute.name, [
- b.stmt(
- serialize_set_binding(assignment, context, () => context.visit(assignment), false)
- )
+ b.stmt(serialize_set_binding(assignment, context, () => context.visit(assignment)))
  ])
  );
  }
@@ -1025,7 +1023,7 @@ function serialize_bind_this(bind_this, context, node) {
  const bind_this_id = /** @type {import('estree').Expression} */ (context.visit(bind_this));
  const ids = Array.from(each_ids.values()).map((id) => b.id('$$value_' + id[0]));
  const assignment = b.assignment('=', bind_this, b.id('$$value'));
- const update = serialize_set_binding(assignment, context, () => context.visit(assignment), false);
+ const update = serialize_set_binding(assignment, context, () => context.visit(assignment));
 
  for (const [binding, [, , expression]] of each_ids) {
  // reset expressions to what they were before
@@ -2399,7 +2397,7 @@ export const template_visitors = {
  if (assignment.left.type !== 'Identifier' && assignment.left.type !== 'MemberExpression') {
  // serialize_set_binding turns other patterns into IIFEs and separates the assignments
  // into separate expressions, at which point this is called again with an identifier or member expression
- return serialize_set_binding(assignment, context, () => assignment, false);
+ return serialize_set_binding(assignment, context, () => assignment);
  }
  const left = object(assignment.left);
  const value = get_assignment_value(assignment, context);
@@ -2780,7 +2778,7 @@ export const template_visitors = {
  assignment,
  context,
  () => /** @type {import('estree').Expression} */ (visit(assignment)),
- false,
+ null,
  {
  skip_proxy_and_freeze: true
  }

packages/svelte/tests/runtime-runes/samples/state-update/_config.js

@@ -2,6 +2,6 @@ import { test } from '../../test';
 
 export default test({
  test({ assert, logs }) {
- assert.deepEqual(logs, [1, 1, 1, 1]);
+ assert.deepEqual(logs, [1, 1, 1, 1, 4, 4]);
  }
 });

packages/svelte/tests/runtime-runes/samples/state-update/main.svelte

@@ -6,4 +6,6 @@
  console.log(x++);
  console.log(++o.x);
  console.log(o.x++);
+ console.log((o.x += 2));
+ console.log((x += 2));
 </script>