How to add join lines shortcut to Xcode

Add the section below to the file IDETextKeyBindingSet.plist that might be located at:

/Applications/Xcode.app/Contents/Frameworks/IDEKit.framework/Versions/A/Resources/IDETextKeyBindingSet.plist depending where the Xcode app is placed and named.

<key>Custom</key>
<dict>
    <key>Join Lines</key>
    <string>moveDown:, moveToEndOfText:, moveToBeginningOfText:, deleteToBeginningOfLine:, deleteBackward:</string>
    <key>Join Lines Backward</key>
    <string>moveToEndOfText:, moveToBeginningOfText:, deleteToBeginningOfLine:, deleteBackward:</string>
</dict>

Join Lines joins the lines forward, the other one backward.

After the file is saved, Xcode needs to be restarted to load the new setup. In Xcode settings, the keyboard shorts can be configured: