I'm seeing this with every release of Xcode now - 26.4.1, 26.5, 26.7 betas - and I'm targeting a macOS app. FB23991559

I'm also looking for a way to do this. I assume that it's not possible with the currently released version of SwiftData/SwiftUI, and that you'd need to drop back to manually sharing a model container somehow, or present the content that should have been in a separate window in a sheet, meaning you can't present more than one at a time. It's quite limiting.

I ended up updating my CI nodes to run macOS 26 Tahoe, and this error doesn't occur anymore.

I'll do my best to create a small reproducer, but this is part of a very large, somewhat complex workspace. Turning off the new Compilation Caching option in Workspace Settings gets me past this error.

After turning on SWIFT_ENABLE_EXPLICIT_MODULES, it gets a little further, and then spits out a very similar error: Showing Recent Issues /Users/tonyarnold/Documents/Reveal/<unknown>:1:1: error reading '/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/17/include/module.modulemap': No such file or directory /Users/tonyarnold/Documents/Reveal/<unknown>:1:1: failed to emit precompiled module '/Users/tonyarnold/Library/Developer/Xcode/DerivedData/ModuleCache.noindex/ptrcheck-4LS9E3I68COI6XN5HHO8H5O7N.pcm' for module map '/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/17/include/module.modulemap'

I'm seeing the same issue affect my app, Reveal (http://revealapp.com). Even setting up the appropriate NSBonjourServices and NSLocalNetworkUsageDescription entries in an iOS app's property list doesn't allow us to use DNSServiceRegister(…) — all we get is an error: kDNSServiceErr_PolicyDenied. If anyone has a workaround, I'd love to hear it!

Quinn, do you feel like I'd be able to gain more insight by opening a TSI for this? Would you recommend that if I needed more help working out why the initial situation is occurring?

I've filed FB13786010. It's frustrating that this is still happening over a year later.

This happened for me with Xcode 15.3 beta 1 and beta 2, and I've just tested and it's still happening with Xcode 15.3 beta 3. I've reported this as FB13620516.

Thanks, Quinn! That's very informative. For CI, someone also suggested separately that using ephemeral CI environments would also prevent this situation from triggering.