The compiler doesn’t support bridging these types; cast unsafely, and note it is so.

Author: millenomi

Foundation/NSError.swift

@@ -222,8 +222,8 @@ extension CFError : _NSBridgeable {
 
 public struct _CFErrorSPIForFoundationXMLUseOnly {
     let error: CFError
-    public init(_ error: AnyObject) {
-        self.error = error as! CFError
+    public init(unsafelyAssumingIsCFError error: AnyObject) {
+        self.error = unsafeBitCast(error, to: CFError.self)
     }
 
     public var _nsObject: NSError {

Foundation/XMLDTD.swift

@@ -44,7 +44,7 @@ open class XMLDTD : XMLNode {
 
         guard let node = _CFXMLParseDTDFromData(unsafeBitCast(data as NSData, to: CFData.self), &unmanagedError) else {
             if let error = unmanagedError?.takeRetainedValue() {
-                throw _CFErrorSPIForFoundationXMLUseOnly(error)._nsObject
+                throw _CFErrorSPIForFoundationXMLUseOnly(unsafelyAssumingIsCFError: error)._nsObject
             }
             //TODO: throw a generic error?
             fatalError("parsing dtd from data failed")

Foundation/XMLDocument.swift

@@ -363,7 +363,7 @@ open class XMLDocument : XMLNode {
         if !result,
             let unmanagedError = unmanagedError {
             let error = unmanagedError.takeRetainedValue()
-            throw _CFErrorSPIForFoundationXMLUseOnly(error)._nsObject
+            throw _CFErrorSPIForFoundationXMLUseOnly(unsafelyAssumingIsCFError: error)._nsObject
         }
     }
 

Foundation/XMLParser.swift

@@ -384,7 +384,7 @@ internal func _NSXMLParserExternalSubset(_ ctx: _CFXMLInterface, name: UnsafePoi
 
 internal func _structuredErrorFunc(_ interface: _CFXMLInterface, error: _CFXMLInterfaceError) {
     let cferr = _CFErrorCreateFromXMLInterface(error)
-    let err = _CFErrorSPIForFoundationXMLUseOnly(cferr)._nsObject
+    let err = _CFErrorSPIForFoundationXMLUseOnly(unsafelyAssumingIsCFError: cferr)._nsObject
     let parser = interface.parser
     parser._parserError = err
     if let delegate = parser.delegate {