I've come across an unexpected error during the build process of my AppKit macOS application. I've traced the problem to a selector, but I don't understand why it's happening and why the selector function would cause cascading errors for a wide swath of unrelated files that were building without issue before this occurrence. Error: Stored value type does not match pointer operand type! store %swift.bridge* %28, i64* %5, align 8, !dbg !1304  i64in function $s7Musaeum27ApplicationWindowControllerC9onAddBook33_8D55888026A145BCB0F1FE379539A486LLyyF unknown:0: error: fatal error encountered during compilation; As part of my custom NSToolbar implementation, the action associated with an NSToolbarItem sets the NSButton's action to an @objc selector. For example, this is how the toolbar item is being constructed: swift let image = NSImage(named: Constants.Toolbar.idAddBook) image!.size = NSSize(width: 20, height: 20) let button = NSButton(image: image!, target: self, action: #selector(onAddBook)) button.frame = NSRect(origin: .zero, size: CGSize(width: 35, height: 30)) button.isBordered = false toolbarItem = customToolbarItem(     itemForItemIdentifier: NSToolbarItem.Identifier.addBook.rawValue,     label: NSLocalizedString("Add", comment: ""),     paletteLabel: NSLocalizedString("Add", comment: ""),     toolTip: NSLocalizedString("tool tip add book", comment: ""),     itemContent: button ) I added the stub of the selector function as follows: swift @objc private func onAddBook() { } When the function body is empty, no issues, and the project builds correctly. If I add one trivial line as follows, still no problem: swift @objc private func onAddBook() {      let urls = fileController.selectFile() } However, as soon as I add the following line, all hell breaks loose: swift @objc private func onAddBook() {     let urls = fileController.selectFile() guard let urls = urls, urls.count 0 else { return } } The surprising thing is that I don't encounter this issue with any of the other selectors I've implemented in different parts of the project performing similar functions. I've tried moving the @objc functions to extensions, to other classes, etc., but they all result in the same outcome. I'm thoroughly perplexed and can't seem to work around this issue. Any insight/help would be greatly appreciated.