Unified sources allow you to get away without #including all the files you need in a .cpp file, because some earlier file in the group has probably already included them for you. This means that when you add a new file to the build, and the unified sources get shuffled around, you end up with a long list of build breakages, some platform-specific, that you can only fix by repeating EWS trials. Here's an example: https://bugs.webkit.org/show_bug.cgi?id=189223. That patch added on new file in Source/WebCore/rendering, which required unrelated #include changes in at least: rendering/RenderBlockFlow.cpp: rendering/RenderFrame.cpp: rendering/RenderImage.cpp: How can we solve this? Should we have an EWS that builds non-unified? Can we somehow have the style checker do #include enforcement? Simon