title: Xcode 10 segmentation fault
body: <p>I stumbled upon segmentation fault 11 issue while compiling project on Xcode 10(+ change to swift 4.2), previously was Xcode 9.4.</p>
  
  <p>I attached log, and class if it should help.</p>
  
  <h2>Compile log</h2>
  
  <p>Xcode gave me no clue with compile log - only saying it happened in OptionDto: </p>
  
  <pre><code>    While verifying SIL function "@$s6Wander9OptionDtoVAA0B0Vs5Error_pIegnrzo_AcEsAF_pIeggozo_TR".
   for &lt;&lt;debugloc at "&lt;compiler-generated&gt;":0:0&gt;&gt;0  swift                    0x000000011159e328 llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;) + 40
  1  swift                    0x000000011159d5a5 llvm::sys::RunSignalHandlers() + 85
  2  swift                    0x000000011159e932 SignalHandler(int) + 258
  3  libsystem_platform.dylib 0x00007fff7793bf5a _sigtramp + 26
  4  libsystem_platform.dylib 0x000000011b01c608 _sigtramp + 2741896904
  5  libsystem_c.dylib        0x00007fff776d91ae abort + 127
  6  swift                    0x000000010e8582b9 (anonymous namespace)::SILVerifier::_require(bool, llvm::Twine const&amp;, std::__1::function&lt;void ()&gt; const&amp;) + 633
  7  swift                    0x000000010e873a4c (anonymous namespace)::SILVerifier::checkFullApplySite(swift::FullApplySite) + 636
  8  swift                    0x000000010e85e097 swift::SILInstructionVisitor&lt;(anonymous namespace)::SILVerifier, void&gt;::visit(swift::SILInstruction*) + 11255
  9  swift                    0x000000010e85a01c (anonymous namespace)::SILVerifier::visitSILBasicBlock(swift::SILBasicBlock*) + 1196
  10 swift                    0x000000010e8545f7 swift::SILFunction::verify(bool) const + 7095
  11 swift                    0x000000010e857693 swift::SILModule::verify() const + 211
  12 swift                    0x000000010e2b4971 swift::Lowering::SILGenModule::~SILGenModule() + 33
  13 swift                    0x000000010e2bfc44 swift::SILModule::constructSIL(swift::ModuleDecl*, swift::SILOptions&amp;, swift::FileUnit*) + 1460
  14 swift                    0x000000010e2bfd4c swift::performSILGeneration(swift::FileUnit&amp;, swift::SILOptions&amp;) + 44
  15 swift                    0x000000010da30df2 performCompile(swift::CompilerInstance&amp;, swift::CompilerInvocation&amp;, llvm::ArrayRef&lt;char const*&gt;, int&amp;, swift::FrontendObserver*, swift::UnifiedStatsReporter*) + 7186
  16 swift                    0x000000010da2e14d swift::performFrontend(llvm::ArrayRef&lt;char const*&gt;, char const*, void*, swift::FrontendObserver*) + 3021
  17 swift                    0x000000010d9e018e main + 686
  18 libdyld.dylib            0x00007fff7762d015 start + 1
  error: Abort trap: 6
  </code></pre>
  
  <p>and also when I downloaded snapshot:</p>
  
  <pre><code>  SIL verification failed: apply doesn't have right number of arguments for function: site.getNumArguments() == substConv.getNumSILArguments()
  Verifying instruction:
     %0 = argument of bb0 : $OptionDto              // user: %2
     %1 = argument of bb0 : $@callee_guaranteed (@in_guaranteed OptionDto) -&gt; (@out Option, @error Error) // user: %2
  -&gt;   try_apply %1(%0) : $@callee_guaranteed (@in_guaranteed OptionDto) -&gt; (@out Option, @error Error), normal bb1, error bb2 // id: %2
  In function:
  // thunk for @escaping @callee_guaranteed (@in_guaranteed OptionDto) -&gt; (@out Option, @error @owned Error)
  sil shared [transparent] [serializable] [thunk] @$s6Wander9OptionDtoVAA0B0Vs5Error_pIegnrzo_AcEsAF_pIeggozo_TR : $@convention(thin) (@guaranteed OptionDto, @guaranteed @callee_guaranteed (@in_guaranteed OptionDto) -&gt; (@out Option, @error Error)) -&gt; (@owned Option, @error Error) {
  // %0                                             // user: %2
  // %1                                             // user: %2
  bb0(%0 : @guaranteed $OptionDto, %1 : @guaranteed $@callee_guaranteed (@in_guaranteed OptionDto) -&gt; (@out Option, @error Error)):
    try_apply %1(%0) : $@callee_guaranteed (@in_guaranteed OptionDto) -&gt; (@out Option, @error Error), normal bb1, error bb2 // id: %2
  
  // %3                                             // user: %4
  bb1(%3 : @trivial $()):                           // Preds: bb0
    return %3 : $()                                 // id: %4
  
  // %5                                             // users: %7, %6
  bb2(%5 : @owned $Error):                          // Preds: bb0
    %6 = builtin "willThrow"(%5 : $Error) : $()
    throw %5 : $Error                               // id: %7
  } // end sil function '$s6Wander9OptionDtoVAA0B0Vs5Error_pIegnrzo_AcEsAF_pIeggozo_TR'
  </code></pre>
  
  <h2>OptionDto</h2>
  
  <pre><code>import ObjectMapper
  struct OptionDto {
      var correctAnswer: Bool?
      var id: Int?
      var optionText: String?
      var task: Int?
  }
  
  extension OptionDto: Mappable {
      init?(map: Map) {}
  
      mutating func mapping(map: Map) {
          correctAnswer &lt;- map["correctAnswer"]
          id &lt;- map["id"]
          optionText &lt;- map["optionText"]
          task &lt;- map["task"]
      }
  }
  </code></pre>