Add #1588 to changelogs

CHANGELOG.md

@@ -210,6 +210,12 @@
   * Don't log if partial or no header typeID is read.  It happens too often due to `.beam` files being written partially to disk during the build process.  They will be re-indexed when they are complete.
 * [#1587](https://github.com/KronicDeth/intellij-elixir/pull/1587) - [@KronicDeth](https://github.com/KronicDeth)
   * Update gradle intellij plugin to fix `runIde` on newer macOS.
+* [#1588](https://github.com/KronicDeth/intellij-elixir/pull/1588) - [@KronicDeth](https://github.com/KronicDeth)
+  * Fix `ConcurrentModificationException` in Structure View
+
+    Java 9 fixed a bug (https://bugs.openjdk.java.net/browse/JDK-8071667) in `HashMap` where `computeIfAbsent` did not check for concurrent modifications, and it turns out that `TreeElementList` was using concurrent modifications, so it was now broke.
+
+    Fixed by use `get` or `put` if it is absent, so that `putNew` can ensure that the `CallDefinition` is in the `TreeElementList` before it is added to the `MutableList<TreeElement>`, which was the original reason why there was a `put` inside of `computeIfAbsent`, which would have `put` when the function returned anyway.
 
 ## v11.0.1
 ### Bug Fixes

resources/META-INF/changelog.html

@@ -27,6 +27,22 @@ <h1>v11.1.0</h1>
         written partially to disk during the build process.  They will be re-indexed when they are complete.
       </li>
       <li>Update gradle intellij plugin to fix <code>runIde</code> on newer macOS.</li>
+      <li>
+        <p>Fix <code>ConcurrentModificationException</code> in Structure View</p>
+        <p>
+          Java 9 fixed a bug (
+          <a href="https://bugs.openjdk.java.net/browse/JDK-8071667" rel="nofollow">
+            https://bugs.openjdk.java.net/browse/JDK-8071667
+          </a>) in <code>HashMap</code> where <code>computeIfAbsent</code> did not check for concurrent modifications,
+          and it turns out that <code>TreeElementList</code> was using concurrent modifications, so it was now broke.
+        </p>
+        <p>
+          Fixed by use <code>get</code> or <code>put</code> if it is absent, so that <code>putNew</code> can ensure that
+          the <code>CallDefinition</code> is in the <code>TreeElementList</code> before it is added to the
+          <code>MutableList&lt;TreeElement&gt;</code>, which was the original reason why there was a <code>put</code>
+          inside of <code>computeIfAbsent</code>, which would have <code>put</code> when the function returned anyway.
+        </p>
+      </li>
     </ul>
   </li>
 </ul>