Swift compiler segmentation fault when building

Adding a (convenient) computed height property to UIView in my UIViewExtension.swift file is causing the Swift compiler to segfault… What could possibly be going wrong here?

0  swift                    0x00000001061e5608 llvm::sys::PrintStackTrace(__sFILE*) + 40
1  swift                    0x00000001061e5af4 SignalHandler(int) + 452
2  libsystem_platform.dylib 0x00007fff894da5aa _sigtramp + 26
3  libsystem_platform.dylib 0xb03939841e997c88 _sigtramp + 2504775416
4  swift                    0x00000001064c8bb9 swift::NominalTypeDecl::getMembers(bool) const + 41
5  swift                    0x00000001055efab9 swift::irgen::ClassMetadataLayout<(anonymous namespace)::FindClassMethodIndex>::addClassMembers(swift::ClassDecl*) + 329
6  swift                    0x00000001055e97b2 swift::irgen::emitVirtualMethodValue(swift::irgen::IRGenFunction&, llvm::Value*, swift::SILType, swift::SILDeclRef, swift::CanTypeWrapper<swift::SILFunctionType>, swift::ResilienceExpansion) + 434
7  swift                    0x00000001056550d3 swift::SILVisitor<(anonymous namespace)::IRGenSILFunction, void>::visit(swift::ValueBase*) + 42611
8  swift                    0x000000010564a266 swift::irgen::IRGenModule::emitSILFunction(swift::SILFunction*) + 8678
9  swift                    0x00000001055cb6f8 swift::irgen::IRGenModule::emitGlobalTopLevel() + 184
10 swift                    0x00000001056376e3 performIRGeneration(swift::IRGenOptions&, swift::Module*, swift::SILModule*, llvm::StringRef, llvm::LLVMContext&, swift::SourceFile*, unsigned int) + 1859
11 swift                    0x0000000105638033 swift::performIRGeneration(swift::IRGenOptions&, swift::SourceFile&, swift::SILModule*, llvm::StringRef, llvm::LLVMContext&, unsigned int) + 51
12 swift                    0x00000001055aa65a frontend_main(llvm::ArrayRef<char const*>, char const*, void*) + 4842
13 swift                    0x00000001055a935d main + 1533
14 libdyld.dylib            0x00007fff8a82e5fd start + 1


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  • 1.  While emitting IR SIL function @_TFCSo6UIViewg6heightSd for 'anonname=0x7ff422892fd0' at <path redacted>/UIViewExtension.swift:60:5
    <unknown>:0: error: unable to execute command: Segmentation fault: 11
    <unknown>:0: error: swift frontend command failed due to signal (use -v to see invocation)
    Command /Applications/Xcode6-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift failed with exit code 254

    If more information is needed to crack this, just comment. Thanks!


    Here’s a related .xcodeproj that returns this question’s compiler error. Download here

    30 Solutions Collect From Internet About “Swift compiler segmentation fault when building”

    I had this error because I was doing this :

    if(currentMeal?.State == .Deleted){

    instead of

    if(currentMeal!.State == .Deleted){

    so I think optional not unwrapped in if condition can cause this error

    When you run into a compiler segfault in Swift, you don’t get a handy line number and error message. Here’s how you can track the problem down:

    1. Create a new file called SegFaultDebugger.swift in your project.
    2. In this new file, define an extension to the class that’s giving you problems.
    3. Move a group of methods from the main file to SegFaultDebugger.swift.
    4. Compile.

    At this point, one of three things happens:

    • You still get the segfault in the original file: Move the methods from SegFaultDebugger.swift back to the original file and move a different set of methods into SegFaultDebugger.swift. Repeat
    • You get a segfault in SegFaultDebugger.swift: Great! Now use binary search to pin the segfault down to a specific method until you can figure out what construct is causing it.
    • You get meaningful compiler errors: Great! Fix the errors. Once everything compiles, move your methods back into the original file.

    I got this error while extending one of my protocols and mistyped and optional type argument.

    protocol SomeProtocolName: class {
        var someProtocolVariable: String { get set }
        func someProtocolFunction(someProtocolVariable: String)
    // MARK:
    extension SomeProtocolName {
        func someProtocolFunction(someProtocolVariable: String?) {
            self.someProtocolVariable = someProtocolVariable

    The difference in function arguments String in prototype and String? in extension caused Segmentation Fault 11.

    I had this error too, and I fixed it like this:

    Check your project and find out which files are used twice and remove one, or delete and re-add them all.

    Errors in my Xcode:

    :0: error: filename “AttributedString.swift” used twice:
    ‘/Users/…/CNJOB/CNJOB/AttributedString.swift’ and

    :0: note: filenames are used to distinguish private
    declarations with the same name

    :0: error: filename “APIClient.swift” used twice:
    ‘/Users/…/CNJOB/CNJOB/APIClient.swift’ and

    :0: note: filenames are used to distinguish private
    declarations with the same name

    Command /Applications/Xcode
    failed with exit code 1

    In Xcode 7, you can click on the error in the Debug Navigator and you’ll be shown an expanded view of the crashes. Clicking on the hamburger button on the right expands the error, and if you scroll all the way down to the bottom of the expanded error message, you will see where it comes from.

    enter image description here

    For me, I had two of those segmentation fault errors. In the picture above, the first one is what it looks like when collapsed, the second is when you expand the hamburger button. At the very bottom of the expanded gray box, you’ll see a message that says where the compiler crashed.

    Note however that the error message may at times be not informative enough, so while it tells you where it crashed, it doesn’t always say why and how to fix it. Getting rid of this error is still very much a matter of guesswork.

    I’ve discovered a simple workaround until the problem is fixed in a future Xcode/Swift build:

    • Simply place all extensions causing the issue in the .swift file that it’s being used.

    In the example project you provided, place the contents of UIViewExtension.swift and CALayerExtension.swift above AppDelegate.swift

    Hopefully this can get us to write working Swift code until the problem’s cleared up.

    As for me, adding private to static var fixed clang crash:

    private static var taskId = 0

    I had a compiler segmentation fault on a statement like this:

    someFunction(isFlagged ? "String1" : "String2")

    I just did a if-else statement instead and it works.

    You can also have this problem if you declare a condition with an unwrapped Bool as a property

    In my case, a misplaced colon during string interpolation broke mine (XCode 6.1.1).



    when I meant to do:

    println("\(value1) : \(value2)")

    This error happened to me when I tried to override weak variable from parent class.

    In base class:

    weak var stripeViewDelegate : StripeViewDelegate? = nil    

    Derived class:

    override weak var stripeViewDelegate : StripeViewDelegate? = nil {
        didSet {
            self.stripeView.delegate = stripeViewDelegate

    The error disappeared when I removed =nil from derived class.

    I catch some exception today

    class func createByAny(instance: Any?) -> ApiCollectionResponse { ... }

    and this solved it:

    class func createByAny(instance: Any) -> ApiCollectionResponse { ... }

    Because “Any” type is any type event “nil”, “AnyObject”, optional, … 🙂
    It is cannot be optional, it is already optional.

    typealias Any = protocol<>

    This error happens also if you accidentally declare a variable with a type matching its name:

        var sectionGroup: sectionGroup? { ... }

    Ran into this error because of an extraneous generic type on an operator function, e.g.

    func ==<T>(lhs: Foo, rhs: Foo) -> Bool {
      return lhs.bar == rhs.bar

    In my case, removing <T> resolved the issue.

    In my case I had declared a struct inside a func. Moving the struct to class level solved the issue.

    Now that I write this I remember having had issues with struct inside funcs before. It was something else than the segmentation fault (which seems to become notorious with the Swift 1.2 beta). OMG Apple, what are you doing there?

    In my case, this error because I use Class name for variable

    var MYClass : MYClass {
        get {

    And this fixes my problem

    var myClass : MYClass {
        get {

    Im my case, this happened when I did incorrect static initialization in a protocol. I found a way to get around, but a compiler should never produce a segmentation fault while building.

    There are three files involved. A protocol NamedSegues.swift, a custom TableViewController that among other things implements the protocol which contains a callback, a custom TableViewCell that holds reference to this protocol to call the callback.

    import Foundation
    protocol NamedSegues {
        func  executeSegueWithId(id: String) -> Void
        static func getDefault() -> NamedSegues  // This was required because of init requirement in CustomCellView
    class CustomController: UITableViewController, NamedSegues {
    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
                let cell = tableView.dequeueReusableCellWithIdentifier("CustomCellID", forIndexPath: indexPath ) as! CustomCellView
            // Configure the cell...
           //App logic...
            cell.parent = self
     //Mark: NamedSegues
         func executeSegueWithId(id: String) ->() {
            NSLog("Received callback to execute segue: \(id)")
        static func getDefault() -> NamedSegues { // I think this must be where it threw up.
            return self as! NamedSegues
    import UIKit
    class CustomCellView: UITableViewCell {
        var id: String = "NoName"
        var parent: NamedSegues = NamedSegues.getDefault() // This is where it was needed.
    override func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent) {
            NSLog("Touched id: \(id)")
                 parent.executeSegueWithId(id) // This is where parent was used.

    I got around it by using ?

    In the protocol file, file1: delete the declaration of getDefault()
    In the CustomController file2: delete the implementation of getDefault.
    In the CustomCellView, file3:

        var parent: NamedSegues?

    The compiler should have caught this and given some error message instead of throwing a segmentation fault during build!

    Seems like the Swift 2 compiler might not have been quite ready for prime-time! In case this helps anyone, I was getting a segmentation fault: 11 due to a mismatch with the variable type in a closure header, specifically in a Parse method, PFQuery.query.findObjectsInBackgroundWithBlock.

    You can see the issue in more detail here:

    Like @Fjohn said, this was an issue related to unwrapping an optional for me (broke in both Xcode 7.0 beta 6 and Xcode 7). In my case, I was not unwrapping optional of the optional (what tipped me off was double ?? in the descriptor. Using if let solved the issue

    double optional causing segmentation fault

    As others wrote above, for me this happened when I’m using an extension over a protocol but the signature of methods in the protocol don’t match the implementations in an extension.

    In my case, I had added a new parameter to the implementation (in the extension) but forgot to also add it to the method’s signature in the protocol.

    This typically happens when the compiler does not have enough information (despite what you think) to guarantee/determine the state of a statement or a variable within a statement.

    For example, imagine you have a dictionary of type [String: String] which you populate with city names as keys and a comma separated list of corresponding zip codes/post codes.

    Imagine that somewhere in your code you want to update the list of corresponding codes:

    myDict[town] += newZipCode + ","

    In this case, the compiler will respond with segmentation fault as town might not be in the dictionary and therefore it cannot guarantee that the above statement will have a valid value.

    To resolve this, you should store the current state of myDict[town] in a separate variable allowing you to handle the case of key not in dict and then update the value for the given key:

    myDict[town] = guaranteedValue + "," newZipCode + ","

    Unfortunately, it is not always straightforward to determine the root cause so I hope this simple example helps.

    Swift 3.0 (Xcode 8.1) exhibits this issue when a protocol declares an optional variable, and an implementer implements that variable as a lazy initialised one.

    Bug is reported here:

    Xcode 8.2.

    Adding @nonobjc protocol implementation into extension causing segmentation faults.
    Move @nonobjc protocol implementation into class implementation.

    For me the following caused a segfault while type is an optional:

    switch type {
        case .aType:
            // Do Something

    and this solved it:

    switch type {
        case .Some(.aType):
            // Do Something

    I got this error with the following method signature in a custom UITableViewController.

    func filterContentForSearchText(searchText: String)

    changing to:

    func filterContentForSearchText(searchText: String!)

    fixed the problem.

    I had the same problem in an extension. My extension had two convenience initializers:

    convenience init(context: NSManagedObjectContext) {
        let entityDescription = NSEntityDescription.entityForName("PropertyEntity", inManagedObjectContext: context)!
        self.init(entity: entityDescription, insertIntoManagedObjectContext: context)
    convenience init(dictionary: NSDictionary, context: NSManagedObjectContext) {
        self.init(context: context)
        property1 = (dictionary["key"] as? String) ?? ""
        // More properties...

    To get rid of the error I added an instance method map(dictionary: NSDictionary) and the segmentation fault error disappeared.

    convenience init(dictionary: NSDictionary, context: NSManagedObjectContext) {
        self.init(context: context)

    For me the issue was having my architectures not set to the standard. I had added i386 or something, just set it back to default xcodeproject arch and it compiled fine.

    I had the same problem in a swift project. The issue was a function that should have returned an object, but didn’t have a return in it. This sort of error used to be signaled while editing with Obj-C. It seems like t isn’t the case in Swift.

    It looks like it can be caused by a lot of reasons lol. In my case it was the pch file – when I tried to import the .pch file in bridging-header.h I got the segmentation fault and I assume maybe it’s caused by the PROJECT-swift.h inside. So what I should do is putting everything swift needs into another const.h and #import "const.h" in both .pch and bridgng-header.h. This is a pretty dumb mistake I made but hope it can help some random guys come cross.

    Discovered yet another way to get this error while attempting to use an empty struct with Argo:

    Causes Segmentation Fault 11:

    struct Action {
    //  let foo: String
    extension Action: Decodable {
      static func decode(json: JSON) -> Decoded<Action> {
        return .MissingKey("foo")

    Compiles just fine:

    struct Action {
      let foo: String
    extension Action: Decodable {
      static func decode(json: JSON) -> Decoded<Action> {
        return .MissingKey("foo")