struct Object {
    var id: String
    var string: String
}

struct Data {
    var string: String
    var tap: ((Object) -> Void)?
}

class TestClass {
    var data: Data?

    func crash() {
        guard let data = data else { return }
        foo(a: "", tap: data.tap)
    }

    @discardableResult
    private func foo(a: String, tap: ((Object) -> Void)?) -> [String] {
        return []
    }
}

0  swift                    0x000000010a10fffa PrintStackTraceSignalHandler(void*) + 42
1  swift                    0x000000010a10f3b6 SignalHandler(int) + 966
2  libsystem_platform.dylib 0x00007fff6675df5a _sigtramp + 26
3  libsystem_platform.dylib 0x00007f0100000008 _sigtramp + 2575966408
4  swift                    0x00000001067bc24d llvm::IRBuilder<llvm::ConstantFolder, llvm::IRBuilderDefaultInserter>::CreateCast(llvm::Instruction::CastOps, llvm::Value*, llvm::Type*, llvm::Twine const&) + 77
5  swift                    0x00000001068cdcca swift::irgen::reemitAsUnsubstituted(swift::irgen::IRGenFunction&, swift::SILType, swift::SILType, swift::irgen::Explosion&, swift::irgen::Explosion&) + 522
6  swift                    0x0000000106955da9 emitApplyArgument((anonymous namespace)::IRGenSILFunction&, swift::SILValue, swift::SILType, swift::irgen::Explosion&) + 393
7  swift                    0x0000000106955119 (anonymous namespace)::IRGenSILFunction::visitFullApplySite(swift::FullApplySite) + 2569
8  swift                    0x0000000106932ff1 swift::irgen::IRGenModule::emitSILFunction(swift::SILFunction*) + 9073
9  swift                    0x0000000106828070 swift::irgen::IRGenerator::emitGlobalTopLevel() + 1024
10 swift                    0x0000000106914527 performIRGeneration(swift::IRGenOptions&, swift::ModuleDecl*, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule> >, llvm::StringRef, llvm::LLVMContext&, swift::SourceFile*, llvm::GlobalVariable**, unsigned int) + 1399
11 swift                    0x000000010676fdce performCompile(swift::CompilerInstance&, swift::CompilerInvocation&, llvm::ArrayRef<char const*>, int&, swift::FrontendObserver*, swift::UnifiedStatsReporter*) + 38110
12 swift                    0x0000000106764e64 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 7908
13 swift                    0x00000001067198b5 main + 18917
14 libdyld.dylib            0x00007fff6644f015 start + 1