Merge pull request #1582 from millenomi/bridging-darwin-fixes-4.2

[4.2][SR-7865] swift-corelibs-foundation does not compile on macOS after 'as' bridging was merged

Author: millenomi

Foundation/Bridging.swift

@@ -12,10 +12,24 @@
 
 import CoreFoundation
 
+#if canImport(ObjectiveC)
+import ObjectiveC
+#endif
+
 public protocol _StructBridgeable {
     func _bridgeToAny() -> Any
 }
 
+fileprivate protocol Unwrappable {
+    func unwrap() -> Any?
+}
+
+extension Optional: Unwrappable {
+    func unwrap() -> Any? {
+        return self
+    }
+}
+
 /// - Note: This does not exist currently on Darwin but it is the inverse correlation to the bridge types such that a 
 /// reference type can be converted via a callout to a conversion method.
 public protocol _StructTypeBridgeable : _StructBridgeable {
@@ -54,18 +68,92 @@ internal protocol _NSBridgeable {
 }
 
 
+#if !canImport(ObjectiveC)
+// The _NSSwiftValue protocol is in the stdlib, and only available on platforms without ObjC.
+extension _SwiftValue: _NSSwiftValue {}
+#endif
+
 /// - Note: This is an internal boxing value for containing abstract structures
-internal final class _SwiftValue : NSObject, NSCopying, _NSSwiftValue {
+internal final class _SwiftValue : NSObject, NSCopying {
     public private(set) var value: Any
 
     static func fetch(_ object: AnyObject?) -> Any? {
         if let obj = object {
-            return fetch(nonOptional: obj)
+            let value = fetch(nonOptional: obj)
+            if let wrapper = value as? Unwrappable, wrapper.unwrap() == nil {
+                return nil
+            } else {
+                return value
+            }
         }
         return nil
     }
 
+    #if canImport(ObjectiveC)
+    private static var _objCNSNullClassStorage: Any.Type?
+    private static var objCNSNullClass: Any.Type? {
+        if let type = _objCNSNullClassStorage {
+            return type
+        }
+        
+        let name = "NSNull"
+        let maybeType = name.withCString { cString in
+            return objc_getClass(cString)
+        }
+        
+        if let type = maybeType as? Any.Type {
+            _objCNSNullClassStorage = type
+            return type
+        } else {
+            return nil
+        }
+    }
+    
+    private static var _swiftStdlibSwiftValueClassStorage: Any.Type?
+    private static var swiftStdlibSwiftValueClass: Any.Type? {
+        if let type = _swiftStdlibSwiftValueClassStorage {
+            return type
+        }
+        
+        let name = "_SwiftValue"
+        let maybeType = name.withCString { cString in
+            return objc_getClass(cString)
+        }
+        
+        if let type = maybeType as? Any.Type {
+            _swiftStdlibSwiftValueClassStorage = type
+            return type
+        } else {
+            return nil
+        }
+    }
+    
+    #endif
+    
     static func fetch(nonOptional object: AnyObject) -> Any {
+        #if canImport(ObjectiveC)
+        // You can pass the result of a `as AnyObject` expression to this method. This can have one of three results on Darwin:
+        // - It's a SwiftFoundation type. Bridging will take care of it below.
+        // - It's nil. The compiler is hardcoded to return [NSNull null] for nils.
+        // - It's some other Swift type. The compiler will box it in a native _SwiftValue.
+        // Case 1 is handled below.
+        // Case 2 is handled here:
+        if type(of: object as Any) == objCNSNullClass {
+            return Optional<Any>.none as Any
+        }
+        // Case 3 is handled here:
+        if type(of: object as Any) == swiftStdlibSwiftValueClass {
+            return object
+            // Since this returns Any, the object is casted almost immediately — e.g.:
+            //   _SwiftValue.fetch(x) as SomeStruct
+            // which will immediately unbox the native box. For callers, it will be exactly
+            // as if we returned the unboxed value directly.
+        }
+        
+        // On Linux, case 2 is handled by the stdlib bridging machinery, and case 3 can't happen —
+        // the compiler will produce SwiftFoundation._SwiftValue boxes rather than ObjC ones.
+        #endif
+        
         if object === kCFBooleanTrue {
             return true
         } else if object === kCFBooleanFalse {
@@ -79,6 +167,13 @@ internal final class _SwiftValue : NSObject, NSCopying, _NSSwiftValue {
         }
     }
 
+    static func store(optional value: Any?) -> NSObject? {
+        if let val = value {
+            return store(val)
+        }
+        return nil
+    }
+    
     static func store(_ value: Any?) -> NSObject? {
         if let val = value {
             return store(val)
@@ -89,8 +184,20 @@ internal final class _SwiftValue : NSObject, NSCopying, _NSSwiftValue {
     static func store(_ value: Any) -> NSObject {
         if let val = value as? NSObject {
             return val
+        } else if let opt = value as? Unwrappable, opt.unwrap() == nil {
+            return NSNull()
         } else {
-            return (value as AnyObject) as! NSObject
+            #if canImport(ObjectiveC)
+                // On Darwin, this can be a native (ObjC) _SwiftValue.
+                let boxed = (value as AnyObject)
+                if !(boxed is NSObject) {
+                    return _SwiftValue(value) // Do not emit native boxes — wrap them in Swift Foundation boxes instead.
+                } else {
+                    return boxed as! NSObject
+                }
+            #else
+                return (value as AnyObject) as! NSObject
+            #endif
         }
     }
 

Foundation/NSArray.swift

@@ -337,7 +337,7 @@ open class NSArray : NSObject, NSCopying, NSMutableCopying, NSSecureCoding, NSCo
             } else {
               let val1 = object(at: idx)
               let val2 = otherArray[idx]
-                if !((val1 as AnyObject) as! NSObject).isEqual(val2 as AnyObject) {
+                if !_SwiftValue.store(val1).isEqual(_SwiftValue.store(val2)) {
                     return false
                 }
             }

Foundation/NSDictionary.swift

@@ -396,9 +396,10 @@ open class NSDictionary : NSObject, NSCopying, NSMutableCopying, NSSecureCoding,
                     return false
                 }
             } else {
-              let otherBridgeable = otherDictionary[key as! AnyHashable]
-              let bridgeable = object(forKey: key)!
-                if !((otherBridgeable as AnyObject) as! NSObject).isEqual(bridgeable as AnyObject) {
+                let otherBridgeable = otherDictionary[key as! AnyHashable]
+                let bridgeable = object(forKey: key)!
+                let equal = _SwiftValue.store(optional: otherBridgeable)?.isEqual(_SwiftValue.store(bridgeable))
+                if equal != true {
                     return false
                 }
             }

Foundation/NSError.swift

@@ -1383,6 +1383,8 @@ enum UnknownNSError: Error {
     case missingError
 }
 
+#if !canImport(ObjectiveC)
+
 public // COMPILER_INTRINSIC
 func _convertNSErrorToError(_ error: NSError?) -> Error {
     return error ?? UnknownNSError.missingError
@@ -1410,3 +1412,6 @@ func _convertErrorToNSError(_ error: Error) -> NSError {
         return NSError(domain: domain, code: code, userInfo: userInfo)
     }
 }
+
+#endif
+

Foundation/NSKeyedArchiver.swift

@@ -597,7 +597,7 @@ open class NSKeyedArchiver : NSCoder {
         object = _replacementObject(objv)
 
         // bridge value types
-        object = object as AnyObject
+        object = _SwiftValue.store(object)
 
         objectRef = _referenceObject(object, conditional: conditional)
         guard let unwrappedObjectRef = objectRef else {

Foundation/NSKeyedUnarchiver.swift

@@ -483,7 +483,7 @@ open class NSKeyedUnarchiver : NSCoder {
                 _cacheObject(object!, forReference: objectRef as! _NSKeyedArchiverUID)
             }
         } else {
-            object = dereferencedObject as AnyObject
+            object = _SwiftValue.store(dereferencedObject)
         }
 
         return _replacementObject(object)

Foundation/NSSet.swift

@@ -46,7 +46,7 @@ open class NSSet : NSObject, NSCopying, NSMutableCopying, NSSecureCoding, NSCodi
         super.init()
         let buffer = UnsafeBufferPointer(start: objects, count: cnt)
         for obj in buffer {
-            _storage.insert(obj as! NSObject)
+            _storage.insert(_SwiftValue.store(obj))
         }
     }