Cannot resolve merge conflicts in 2026.2: Resolve action does nothing for Perforce, SVN, Mercurial

Problem

In IntelliJ-based IDEs 2026.2, invoking merge-conflict resolution has no visible effect: the Merge Conflicts dialog does not open and no error appears in the UI. Both entry points are affected:

• The Resolve link on the Merge Conflicts node of the Local Changes view
• Any menu action that opens the merge dialog for the conflicting files

The IDE log contains:

java.lang.IndexOutOfBoundsException: Index 1 out of bounds for length 1
	at java.base/java.util.ArrayList.get(ArrayList.java:428)
	at com.intellij.openapi.vcs.merge.flow.IterativeMergeFlowDelegate.installTableContextMenu(IterativeMergeFlowDelegate.kt:382)
	at com.intellij.openapi.vcs.merge.flow.IterativeMergeFlowDelegate.createCenterPanel(IterativeMergeFlowDelegate.kt:144)
	at com.intellij.openapi.vcs.merge.MultipleFileMergeDialog.createCenterPanel(MultipleFileMergeDialog.kt:174)
	at com.intellij.openapi.vcs.merge.MultipleFileMergeDialog.<init>(MultipleFileMergeDialog.kt:167)

Affected builds: 2026.2 Beta (262.8665.81) through 2026.2.0.1. Reported with Perforce, Subversion, and Mercurial repositories in IntelliJ IDEA, JetBrains Rider, and CLion. Git repositories are not affected.

Cause

The registry key vcs.merge.conflict.iterative.resolution changed its default from false to true in 2026.2 Beta. This routes the merge dialog through IterativeMergeFlowDelegate instead of the previous OneShotMergeFlowDelegate.

Tracked in vcs.merge.conflict.iterative.resolution causes java.lang.IndexOutOfBoundsException.

Resolution

Update to 2026.2.1, which contains the fix.

To restore conflict resolution on 2026.2, disable the registry key:

1. Press Shift twice to open Search Everywhere.
2. Type Registry.. and open the Registry dialog.
3. Find the vcs.merge.conflict.iterative.resolution key and clear its checkbox.
4. Click Close.
5. Restart the IDE.

Disabling the key returns the merge dialog to its pre-2026.2 implementation. Conflict resolution remains fully functional; only the iterative-resolution UI introduced in 2026.2 is unavailable.