Attach Sources dialog: JAR files not visible in IntelliJ IDEA 2026.2 – Support | JetBrains

Problem

Opening the Attach Sources dialog via Choose Sources... in the decompiled class editor banner shows only directories — JAR files are not visible and cannot be selected. The issue occurs in IntelliJ IDEA 2026.2 and does not reproduce in 2026.1.3.

Errors appear in idea.log:

java.lang.IllegalStateException: AWT-EventQueue-0
    at com.intellij.openapi.fileChooser.universal.NioFileTreeModel$State.getRoots(NioFileTreeModel.kt:225)

java.util.ConcurrentModificationException
    at com.intellij.openapi.fileChooser.universal.UniversalFileChooser$Panel$FileView$startCacheUpdates$1$1.invokeSuspend(UniversalFileChooser.kt:797)

Cause

IntelliJ IDEA 2026.2 introduced a new file chooser implementation (UniversalFileChooser) as the default. Two threading bugs prevent files from loading in the dialog:

IllegalStateException in NioFileTreeModel.getRoots() — invoked on the Event Dispatch Thread where it must not run.
ConcurrentModificationException in the cache-update coroutine — an ArrayList of roots is iterated while being modified concurrently.

The issue is tracked in Existing source JAR not visible in 'Attach Sources' dialog and can't be selected (2026.2) using new universal file chooser.

Resolution

Open Registry (Press ⇧Shift twice to open the search window → Actions → Registry...), then find key universal.file.chooser.is.enabled and unset the checkbox. Attach the file again, now the source JAR file will be visible.

For full resolution, update IntelliJ IDEA once a patch that fixes Existing source JAR not visible in 'Attach Sources' dialog and can't be selected (2026.2) using new universal file chooser becomes available, or downgrade to IntelliJ IDEA 2026.1.4 where the issue does not occur.