Changed code is a nightmare. This is unanimously agreed by the community of developers across the world. To control change, there are versioning systems available. These can show you in detail that a file has changed whenever you upload your changed file to the versioning server. However, who is responsible for the changes you make to your local working copy? How are you going to track which change caused your code to break down?
You can use file comparisons. Since PhpStorm records each and every activity that you perform on the editor, you can find out the actual nonworking code by comparing your troublesome file across different timelines. If you feel timelines is an alien here, you might feel easy to know that PhpStorm actually saves your local copy versions according to timestamps. If at some point in time, your code stops working and undo will not help, you can use file comparison to review the timeline and compare the historical file with your current file...