From 90f2a06b5e892ac08e989f5809e2e371ee101ec4 Mon Sep 17 00:00:00 2001
From: Kevin Jahns <kevin.jahns@protonmail.com>
Date: Tue, 27 Jun 2023 13:20:53 +0200
Subject: [PATCH] throw error when event changes are computed after a
 transaction

---
 src/utils/YEvent.js  |  9 +++++++++
 tests/y-map.tests.js | 23 +++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/src/utils/YEvent.js b/src/utils/YEvent.js
index 8aafd94f..b47d8c9a 100644
--- a/src/utils/YEvent.js
+++ b/src/utils/YEvent.js
@@ -6,6 +6,9 @@ import {
 
 import * as set from 'lib0/set'
 import * as array from 'lib0/array'
+import * as error from 'lib0/error'
+
+const errorComputeChanges = 'You must not compute changes after the event-handler fired.'
 
 /**
  * @template {AbstractType<any>} T
@@ -84,6 +87,9 @@ export class YEvent {
    */
   get keys () {
     if (this._keys === null) {
+      if (this.transaction.doc._transactionCleanups.length === 0) {
+        throw error.create(errorComputeChanges)
+      }
       const keys = new Map()
       const target = this.target
       const changed = /** @type Set<string|null> */ (this.transaction.changed.get(target))
@@ -167,6 +173,9 @@ export class YEvent {
   get changes () {
     let changes = this._changes
     if (changes === null) {
+      if (this.transaction.doc._transactionCleanups.length === 0) {
+        throw error.create(errorComputeChanges)
+      }
       const target = this.target
       const added = set.create()
       const deleted = set.create()
diff --git a/tests/y-map.tests.js b/tests/y-map.tests.js
index 3356afc1..346bd746 100644
--- a/tests/y-map.tests.js
+++ b/tests/y-map.tests.js
@@ -8,6 +8,29 @@ import * as Y from '../src/index.js'
 import * as t from 'lib0/testing'
 import * as prng from 'lib0/prng'
 
+/**
+ * Computing event changes after transaction should result in an error. See yjs#539
+ *
+ * @param {t.TestCase} _tc
+ */
+export const testMapEventError = _tc => {
+  const doc = new Y.Doc()
+  const ymap = doc.getMap()
+  /**
+   * @type {any}
+   */
+  let event = null
+  ymap.observe((e) => {
+    event = e
+  })
+  t.fails(() => {
+    t.info(event.keys)
+  })
+  t.fails(() => {
+    t.info(event.keys)
+  })
+}
+
 /**
  * @param {t.TestCase} tc
  */