WidgetBundleBuilder crash on #available(iOS 18.0) check: WidgetBundleBuilder includes an unknown OS version

Workaround:

Check #available(iOS 18.0, *) at the top level, without using WidgetBundleBuilder.

Please let us know if you run into additional issues.

The situation gets even worse if you need to triple-check to support, for example, older widgets without interaction, iOS 17 widgets with interaction, and the new iOS 18 control widgets.

If you use the above workaround with three versions, it will result in an error: Function declares an opaque return type 'some Widget', but the return statements in its body do not have matching underlying types

Code with error:

var body: some Widget {
		if #available(iOS 18.0, *) {
			return body_iOS18
		} else if #available(iOS 17.0, *) {
			return body_iOS17
		} else {
			return body_old
		}
	}

So you have to create ugly things like:

var body: some Widget {
		if #available(iOS 17.0, *) {
			return body_new
		} else {
			return body_old
		}
	}
	
	@available(iOSApplicationExtension 17.0, *)
	var body_new: some Widget {
		if #available(iOS 18.0, *) {
			return body_iOS18
		} else {
			return body_iOS17
		}
	}

You can modify this slightly to handle iOS 18

https://stackoverflow.com/questions/76864560/is-there-a-way-to-provide-ios-version-check-inside-widget-extension/77082330#77082330

This issue is fixed in Xcode 16.1 beta 3 with the updated SDKs. Thanks for filing the feedback!