Re-shim tagged NSString creation

stdlib/public/Darwin/Foundation/String.swift

@@ -96,3 +96,28 @@ extension Substring : _ObjectiveCBridgeable {
 }
 
 extension String: CVarArg {}
+
+/*
+ This is on NSObject so that the stdlib can call it in StringBridge.swift
+ without having to synthesize a receiver (e.g. lookup a class or allocate)
+
+ In the future (once the Foundation overlay can know about SmallString), we
+ should move the caller of this method up into the overlay and avoid this
+ indirection.
+ */
+private extension NSObject {
+  // The ObjC selector has to start with "new" to get ARC to not autorelease
+  @_effects(releasenone)
+  @objc(newTaggedNSStringWithASCIIBytes_:length_:)
+  func createTaggedString(bytes: UnsafePointer<UInt8>,
+                          count: Int) -> AnyObject? {
+    //TODO: update this to use _CFStringCreateTaggedPointerString once we can
+    return CFStringCreateWithBytes(
+      kCFAllocatorSystemDefault,
+      bytes,
+      count,
+      CFStringBuiltInEncodings.UTF8.rawValue,
+      false
+    ) as NSString as NSString? //just "as AnyObject" inserts unwanted bridging
+  }
+}

stdlib/public/SwiftShims/CoreFoundationShims.h

@@ -28,29 +28,17 @@ namespace swift { extern "C" {
 
 #ifdef __OBJC2__
 #if __LLP64__
-typedef unsigned long long _swift_shims_CFTypeID;
 typedef unsigned long long _swift_shims_CFHashCode;
 typedef signed long long _swift_shims_CFIndex;
 #else
-typedef unsigned long _swift_shims_CFTypeID;
 typedef unsigned long _swift_shims_CFHashCode;
 typedef signed long _swift_shims_CFIndex;
 #endif
 
-typedef id _swift_shims_CFStringRef;
-typedef __swift_uint32_t _swift_shims_CFStringEncoding;
-
 // Consider creating SwiftMacTypes.h for these
 typedef unsigned char _swift_shims_Boolean;
 typedef __swift_uint8_t _swift_shims_UInt8;
-
-SWIFT_RUNTIME_STDLIB_API
-__attribute__((ns_returns_retained))
-_swift_shims_CFStringRef _Nonnull _swift_stdlib_CFStringCreateWithBytes(
-    const void * _Nullable unused,
-    const __swift_uint8_t *_Nonnull bytes, _swift_shims_CFIndex numBytes,
-    _swift_shims_CFStringEncoding encoding,
-    _swift_shims_Boolean isExternalRepresentation);
+typedef __swift_uint32_t _swift_shims_CFStringEncoding;
 
 SWIFT_RUNTIME_STDLIB_API
 __swift_uint8_t _swift_stdlib_isNSString(id _Nonnull obj);

stdlib/public/core/StringBridge.swift

@@ -58,6 +58,10 @@ internal typealias _CocoaString = AnyObject
                options: UInt,
                range: _SwiftNSRange,
                locale: AnyObject?) -> Int
+
+  @objc(newTaggedNSStringWithASCIIBytes_:length_:)
+  func createTaggedString(bytes: UnsafePointer<UInt8>, 
+                          count: Int) -> AnyObject?
 }
 
 /*
@@ -410,19 +414,28 @@ extension String {
   }
 }
 
+@_effects(releasenone)
+private func _createNSString(
+  _ receiver: _StringSelectorHolder,
+  _ ptr: UnsafePointer<UInt8>,
+  _ count: Int,
+  _ encoding: UInt32
+) -> AnyObject? {
+  return receiver.createTaggedString(bytes: ptr, count: count)
+}
+
 @_effects(releasenone)
 private func _createCFString(
   _ ptr: UnsafePointer<UInt8>,
   _ count: Int,
   _ encoding: UInt32
-) -> AnyObject {
-  return _swift_stdlib_CFStringCreateWithBytes(
-    nil, //ignored in the shim for perf reasons
+) -> AnyObject? {
+  return _createNSString(
+    unsafeBitCast(__StringStorage.self as AnyClass, to: _StringSelectorHolder.self),
     ptr,
     count,
-    kCFStringEncodingUTF8,
-    0
-  ) as AnyObject
+    encoding
+  )
 }
 
 extension String {
@@ -431,13 +444,14 @@ extension String {
   func _bridgeToObjectiveCImpl() -> AnyObject {
     // Smol ASCII a) may bridge to tagged pointers, b) can't contain a BOM
     if _guts.isSmallASCII {
-      return _guts.asSmall.withUTF8 { bufPtr in
+      let maybeTagged = _guts.asSmall.withUTF8 { bufPtr in
         return _createCFString(
           bufPtr.baseAddress._unsafelyUnwrappedUnchecked,
           bufPtr.count,
           kCFStringEncodingUTF8
         )
       }
+      if let tagged = maybeTagged { return tagged }
     }
     if _guts.isSmall {
         // We can't form a tagged pointer String, so grow to a non-small String,

stdlib/public/stubs/FoundationHelpers.mm

@@ -25,38 +25,13 @@
 
 using namespace swift;
 
-template <class FromTy> struct DestType;
-
-#define BRIDGE_TYPE(FROM, TO) \
-template <> struct DestType<FROM> { using type = TO; }
-
-BRIDGE_TYPE(_swift_shims_CFStringRef, CFStringRef);
-BRIDGE_TYPE(_swift_shims_CFStringEncoding, CFStringEncoding);
-BRIDGE_TYPE(CFStringRef, _swift_shims_CFStringRef);
-
-template <class FromTy>
-static typename DestType<FromTy>::type cast(FromTy value) {
-  return (typename DestType<FromTy>::type) value;
-}
-
 __swift_uint8_t
 swift::_swift_stdlib_isNSString(id obj) {
   //TODO: we can likely get a small perf win by using _NSIsNSString on
   //sufficiently new OSs
   return CFGetTypeID((CFTypeRef)obj) == CFStringGetTypeID() ? 1 : 0;
 }
 
-_swift_shims_CFStringRef
-swift::_swift_stdlib_CFStringCreateWithBytes(
-    const void *unused, const uint8_t *bytes,
-    _swift_shims_CFIndex numBytes, _swift_shims_CFStringEncoding encoding,
-    _swift_shims_Boolean isExternalRepresentation) {
-  assert(unused == NULL);
-  return cast(CFStringCreateWithBytes(kCFAllocatorSystemDefault, bytes, numBytes,
-                                      cast(encoding),
-                                      isExternalRepresentation));
-}
-
 extern "C" CFHashCode CFStringHashCString(const uint8_t *bytes, CFIndex len);
 extern "C" CFHashCode CFStringHashNSString(id str);