I don't fully understand the internal issue that occurs when this error happens but I HAVE found a way to solve it on my local system. (Mojave, Xcode 11.7) My particular problem was I inserted the iOS 14 SDK in place of the iOS 13 SDK Xcode 11.7 originally shipped with. It only gave me problems when trying to build any swift code. (which i try to avoid like the plague personally)
I ended up writing a script that changes back and forth between my iOS 14 and iOS 13 SDK folders to temporarily 'solve' the issue, but from further investigation it appears to be what i suspected all along: a need for a updated swift toolchain (so much for ABI stability, eh?)
https://forums.swift.org/t/error-abort-trap-6-when-compiling-using-xcode-12-beta-12a6159-with-swift-5-2-4-release-toolchain/37942
The swift toolchain that ships with newer versions of Xcode must have this function added to 'builtin' (as similarly mentioned on that link above)
I haven't tried installing anything passed swift 5.0 toolchain, but I presume attempting to install a newer one will potentially provide a more proper mitigation of this issue.
EDIT: Upon further investigation installing these toolchains won't let you build to device, however, I did find a bit of a hacky solution if you are ready to get your hands dirty (if this ever happens again, or happens to anyone else)
if you open the following file in a text editor (i did it in vim) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/lib/swift/Swift.swiftmodule/arm64-apple-ios.swiftinterface
and search for 'convertUnownedUnsafeToGuaranteed' you should happen upon this function:
@inlinable @_transparent public func _withUnsafeGuaranteedRef<Result>(_ body: (Instance) throws -> Result) rethrows -> Result {
var tmp = self
// Builtin.convertUnownedUnsafeToGuaranteed expects to have a base value
// that the +0 value depends on. In this case, we are assuming that is done
// for us opaquely already. So, the builtin will emit a mark_dependence on a
// trivial object. The optimizer knows to eliminate that so we do not have
// any overhead from this.
let fakeBase: Int? = nil
return try body(Builtin.convertUnownedUnsafeToGuaranteed(fakeBase,
&tmp._value))
}
you can comment it out using standard /* */ and then put this in its place and it /should/ get passed that error.
@inlinable public func _withUnsafeGuaranteedRef<Result>(_ body: (Instance) throws -> Result) rethrows -> Result {
let (guaranteedInstance, token) = Builtin.unsafeGuaranteed(_value)
let result = try body(guaranteedInstance)
Builtin.unsafeGuaranteedEnd(token)
return result
}
If you are curious where i found this function, its inside the iOS 13.x SDK version of the same file. located at: (if you have an XCode installed with a iOS 13 SDK anywhere) /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/lib/swift/Swift.swiftmodule/arm64.swiftinterface
If you want to see the exact path of the iOS SDK you are building with xcrun can be extremely helpful:
xcrun --sdk iphoneos --show-sdk-path
yields:
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk
Presumably, you would need to repeat these steps for any other architecture you are targeting (ie arm64e-apple-ios.swiftinterface) etc.
