Hi all, For several years now, Xcode has included two build systems: the “legacy” build system and the newer “XCBuild” system (see, for example, <https://developer.apple.com/videos/play/wwdc2018/408/> and <https://developer.apple.com/videos/play/wwdc2018/415>, as well as <https://medium.com/xcblog/xcode-new-build-system-for-speedy-swift-builds-c39ea6596e17> and <https://medium.com/xcblog/five-things-you-must-know-about-xcode-10-new-build-system-41676cd5fd6c>). WebKit is finally in a position to move to the new build system. However, this switch is not without consequences. In particular, WebKit has a complicated build process and requires new XCBuild features only found in Xcode 11.4. If you build from within the IDE, you will need Xcode 11.4 or later. Pre-releases have been available for some time on developer.apple.com, but the final version of Xcode 11.4 was posted to the Mac App Store last week on March 24, 2020. When building from the command line, the conditions are less strict. By default, builds are performed with XCBuild if the `build-webkit` script or the makefiles detect that Xcode 11.4 or later is installed. If not, builds are performed with the legacy build system. We can be flexible here because the build process is controlled by these scripts and makefiles, allowing the build process to determine the Xcode version before invoking `xcodebuild`. There is no such opportunity when building within the Xcode IDE, and so the build requirements are stricter. I’ve made the changes to switch over to XCBuild but I haven’t yet posted them. I want to first find out if this move will cause any issues for developers who — for whatever reason — need to stay on old versions of Xcode. If so, please let me know. — Keith Rollin