Failed to emit precompiled module in Xcode 26b1

Question

Created 1w

Replies 4

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I'm trying to bring up an existing macOS app workspace to build against the macOS 26 SDK, however Xcode 26b1 is producing the following error, and I'm unable to proceed:

/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/_Builtin_stdbool-LVR359SH1U4537HG9T3JOGN.pcm' for module map '/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/17/include/module.modulemap'

I've checked and the module map that it claims is missing is there on the filesystem.

Is this a known issue with this beta?

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Answer 1

tonyarnold OP

1w

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'

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Answer 2

Developer Tools Engineer OP

Apple

1w

Can you please share a small reproducer for this issue?

To me it looks like "XcodeDefault.xctoolchain/usr/lib/clang/17/include/module.modulemap" sometimes is present and sometimes is absent. When it is present, Xcode decides to build modules "_Builtin_stdbool", "ptrcheck". But later when actually building those modules it cannot find the module map. I would expect such behavior when Xcode-beta.app is on external hard drive and that drive not working reliably.

Still, a small reproducer would help us to understand the issue better and to be able to help you.

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Answer 3

tonyarnold OP

1w

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.

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Answer 4

Developer Tools Engineer OP

Apple

6d

@tonyarnold a reproducer would be ideal, but in the meantime a build log where this failed might be helpful to get us started figuring out what went wrong. We wouldn't expect this kind of error to happen when using compilation caching; in that mode the modulemap should only be read during dependency scanning/planning and not when emitting a precompiled module, which is what seems to have happened here. If you can share a full build log (possibly attached to a Feedback) we may be able to figure it out or at least narrow it down.

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