Segmentation fault: 11 - Xcode/Swift 5 compile issue

Question

I'm always getting a Segmentation fault: 11 error when compiling.

I have massively stripped back my code to identify the nuances of what is causing the issue and have produced the demo code below that exhibits the exact same problem.

Can anyone suggest any way to resolve this issue (thats different to what I have already highlight in the code comments)?

PS: this Swift 5 code and occurs with both Xcode 11.7 and Xcode 12

// If we make this a class instead, it compiles! (but I want it to be a struct)
struct SomeStruct {
    // If we remove either of these properties or change them to an Int, it compiles! (but I obviously need 2 strings)
    let propertyA: String
    let propertyB: String
}

protocol Protocol { }

enum Enumeration {

    // If we remove this case, it compiles! (but I need this case, and the protocol also)
    case possibilityA(protocol: Protocol)

    // If we add additional associated values to this case, it compiles! (but I need this case)
    case possibilityB(completion: (Result<SomeStruct, Error>) -> ())
}

class SomeClass {

    func method() {
        // If we remove the use of `possibilityB`, it compiles! (but I need this)
        _ = Enumeration.possibilityB(completion: { _ in
        })
    }
}

Here's the stack dump...

Stack dump:
0.  Program arguments: /Applications/Xcode_12.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift -frontend -c -primary-file /Users/x/Demo/Sources/Demo/Demo.swift -emit-module-path /Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Intermediates.noindex/Demo.build/Debug-iphoneos/Demo.build/Objects-normal/arm64/Demo~partial.swiftmodule -emit-module-doc-path /Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Intermediates.noindex/Demo.build/Debug-iphoneos/Demo.build/Objects-normal/arm64/Demo~partial.swiftdoc -emit-module-source-info-path /Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Intermediates.noindex/Demo.build/Debug-iphoneos/Demo.build/Objects-normal/arm64/Demo~partial.swiftsourceinfo -serialize-diagnostics-path /Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Intermediates.noindex/Demo.build/Debug-iphoneos/Demo.build/Objects-normal/arm64/Demo.dia -emit-dependencies-path /Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Intermediates.noindex/Demo.build/Debug-iphoneos/Demo.build/Objects-normal/arm64/Demo.d -emit-reference-dependencies-path /Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Intermediates.noindex/Demo.build/Debug-iphoneos/Demo.build/Objects-normal/arm64/Demo.swiftdeps -target arm64-apple-ios9.0 -Xllvm -aarch64-use-tbi -enable-objc-interop -sdk /Applications/Xcode_12.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk -I /Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Products/Debug-iphoneos -I /Applications/Xcode_12.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/lib -F /Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Products/Debug-iphoneos -F /Applications/Xcode_12.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/Library/Frameworks -F /Applications/Xcode_12.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.0.sdk/Developer/Library/Frameworks -enable-testing -g -module-cache-path /Users/x/Library/Developer/Xcode/DerivedData/ModuleCache.noindex -swift-version 5 -enforce-exclusivity=checked -Onone -D SWIFT_PACKAGE -D DEBUG -D Xcode -serialize-debugging-options -Xcc -working-directory -Xcc /Users/x/Demo -enable-anonymous-context-mangled-names -Xcc -I/Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Intermediates.noindex/Demo.build/Debug-iphoneos/Demo.build/swift-overrides.hmap -Xcc -I/Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Products/Debug-iphoneos/include -Xcc -I/Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Intermediates.noindex/Demo.build/Debug-iphoneos/Demo.build/DerivedSources-normal/arm64 -Xcc -I/Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Intermediates.noindex/Demo.build/Debug-iphoneos/Demo.build/DerivedSources/arm64 -Xcc -I/Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Intermediates.noindex/Demo.build/Debug-iphoneos/Demo.build/DerivedSources -Xcc -DSWIFT_PACKAGE -Xcc -DDEBUG=1 -target-sdk-version 14.0 -parse-as-library -module-name Demo -o /Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Build/Intermediates.noindex/Demo.build/Debug-iphoneos/Demo.build/Objects-normal/arm64/Demo.o -embed-bitcode-marker -index-store-path /Users/x/Library/Developer/Xcode/DerivedData/Demo-hjukrlyoxxzhqwasgqzluieckmux/Index/DataStore -index-system-modules 
1.  Apple Swift version 5.3 (swiftlang-1200.0.29.2 clang-1200.0.30.1)
2.  While evaluating request IRGenSourceFileRequest(IR Generation for file "/Users/x/Demo/Sources/Demo/Demo.swift")
3.  While emitting IR SIL function "@$s8Demo9SomeClassC6methodyyF".
 for 'method()' (at /Users/x/Demo/Sources/Demo/Demo.swift:21:5)
4.  While converting type '(@callee_guaranteed (@in_guaranteed Result<SomeStruct, Error>) -> ())'
0  swift                    0x0000000107a19865 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 37
1  swift                    0x0000000107a18865 llvm::sys::RunSignalHandlers() + 85
2  swift                    0x0000000107a19e1f SignalHandler(int) + 111
3  libsystem_platform.dylib 0x00007fff68acc5fd _sigtramp + 29
4  libsystem_platform.dylib 0x0000000000000004 _sigtramp + 18446603338760010276
5  swift                    0x00000001039794d8 swift::SILInstructionVisitor<(anonymous namespace)::IRGenSILFunction, void>::visit(swift::SILInstruction*) + 21400
6  swift                    0x000000010396fc26 swift::irgen::IRGenModule::emitSILFunction(swift::SILFunction*) + 8982
7  swift                    0x0000000103809dc7 swift::irgen::IRGenerator::emitGlobalTopLevel(llvm::StringSet<llvm::MallocAllocator>*) + 1607
8  swift                    0x00000001039449d7 performIRGeneration(swift::IRGenOptions const&, swift::ModuleDecl*, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule> >, llvm::StringRef, swift::PrimarySpecificPaths const&, llvm::StringRef, swift::SourceFile*, llvm::GlobalVariable**, llvm::StringSet<llvm::MallocAllocator>*) + 1687
9  swift                    0x000000010396d681 swift::SimpleRequest<swift::IRGenSourceFileRequest, swift::GeneratedModule (swift::IRGenDescriptor), (swift::RequestFlags)9>::evaluateRequest(swift::IRGenSourceFileRequest const&, swift::Evaluator&) + 97
10 swift                    0x0000000103948dec llvm::Expected<swift::IRGenSourceFileRequest::OutputType> swift::Evaluator::getResultUncached<swift::IRGenSourceFileRequest>(swift::IRGenSourceFileRequest const&) + 940
11 swift                    0x000000010394503d swift::performIRGeneration(swift::IRGenOptions const&, swift::SourceFile&, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule> >, llvm::StringRef, swift::PrimarySpecificPaths const&, llvm::StringRef, llvm::GlobalVariable**, llvm::StringSet<llvm::MallocAllocator>*) + 269
12 swift                    0x0000000103590d3a performCompileStepsPostSILGen(swift::CompilerInstance&, swift::CompilerInvocation const&, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule> >, llvm::PointerUnion<swift::ModuleDecl*, swift::SourceFile*>, swift::PrimarySpecificPaths const&, int&, swift::FrontendObserver*) + 3002
13 swift                    0x0000000103580928 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 20712
14 swift                    0x0000000103501c07 main + 1255
15 libdyld.dylib            0x00007fff688d3cc9 start + 1
16 libdyld.dylib            0x000000000000004f start + 18446603338762077063
error: Segmentation fault: 11 (in target 'Demo' from project 'Demo')

Answer 1

Naming the enum associated values is a shadow zone. While it is apparently accepted under certain conditions, it is not used or even mentioned in the official Swift Language Guide chapter on Enumerations. So in this case, your code compiles fine if you remove the naming.

enum Enumeration {
    case possibilityA(Protocol)
    case possibilityB((Result<SomeStruct, Error>) -> ())
}
...
func method() {
    let _ = Enumeration.possibilityB({ _ in
})

In any case, a crashing compiler is never nice, no matter how bad code you feed it, and furthermore you got a pretty cool minimal test, so filling a report should be your duty and honor :)