swift-mirror/stdlib/public/core/StringBridge.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

import SwiftShims

/// Effectively an untyped NSString that doesn't require foundation.
@usableFromInline
internal typealias _CocoaString = AnyObject

#if _runtime(_ObjC)
// Swift's String bridges NSString via this protocol and these
// variables, allowing the core stdlib to remain decoupled from
// Foundation.

@usableFromInline // @testable
@_effects(releasenone)
internal func _stdlib_binary_CFStringCreateCopy(
  _ source: _CocoaString
) -> _CocoaString {
  let result = _swift_stdlib_CFStringCreateCopy(nil, source) as AnyObject
  return result
}

@usableFromInline // @testable
@_effects(readonly)
internal func _stdlib_binary_CFStringGetLength(
  _ source: _CocoaString
) -> Int {
  return _swift_stdlib_CFStringGetLength(source)
}

@usableFromInline // @testable
@_effects(readonly)
internal func _stdlib_binary_CFStringGetCharactersPtr(
  _ source: _CocoaString
) -> UnsafeMutablePointer<UTF16.CodeUnit>? {
  return UnsafeMutablePointer(
    mutating: _swift_stdlib_CFStringGetCharactersPtr(source))
}

/// Copies a slice of a _CocoaString into contiguous storage of sufficient
/// capacity.
@_effects(releasenone)
internal func _cocoaStringCopyCharacters(
  from source: _CocoaString,
  range: Range<Int>,
  into destination: UnsafeMutablePointer<UTF16.CodeUnit>
) {
  _swift_stdlib_CFStringGetCharacters(
    source,
    _swift_shims_CFRange(location: range.lowerBound, length: range.count),
    destination)
}

@_effects(readonly)
internal func _cocoaStringSubscript(
  _ target: _CocoaString, _ position: Int
) -> UTF16.CodeUnit {
  let cfSelf: _swift_shims_CFStringRef = target
  return _swift_stdlib_CFStringGetCharacterAtIndex(cfSelf, position)
}

@_effects(readonly)
internal func _cocoaStringCompare(
  _ string: _CocoaString, _ other: _CocoaString
) -> Int {
  let cfSelf: _swift_shims_CFStringRef = string
  let cfOther: _swift_shims_CFStringRef = other
  return _swift_stdlib_CFStringCompare(cfSelf, cfOther)
}

@_effects(readonly)
internal func _cocoaHashString(
  _ string: _CocoaString
) -> UInt {
  return _swift_stdlib_CFStringHashNSString(string)
}

@_effects(readonly)
internal func _cocoaHashASCIIBytes(
  _ bytes: UnsafePointer<UInt8>, length: Int
) -> UInt {
  return _swift_stdlib_CFStringHashCString(bytes, length)
}

// These "trampolines" are effectively objc_msgSend_super.
// They bypass our implementations to use NSString's.

@_effects(readonly)
internal func _cocoaCStringUsingEncodingTrampoline(
  _ string: _CocoaString, _ encoding: UInt
) -> UnsafePointer<UInt8>? {
  return _swift_stdlib_NSStringCStringUsingEncodingTrampoline(string, encoding)
}

@_effects(releasenone)
internal func _cocoaGetCStringTrampoline(
  _ string: _CocoaString,
  _ buffer: UnsafeMutablePointer<UInt8>,
  _ maxLength: Int,
  _ encoding: UInt
) -> Int8 {
  return Int8(_swift_stdlib_NSStringGetCStringTrampoline(
    string, buffer, maxLength, encoding))
}

//
// Conversion from NSString to Swift's native representation.
//

private var kCFStringEncodingASCII : _swift_shims_CFStringEncoding {
  @inline(__always) get { return 0x0600 }
}

private var kCFStringEncodingUTF8 : _swift_shims_CFStringEncoding {
  @inline(__always) get { return 0x8000100 }
}

@_effects(readonly)
private func _unsafeAddressOfCocoaStringClass(_ str: _CocoaString) -> UInt {
  return _swift_stdlib_unsafeAddressOfClass(str)
}

internal enum _KnownCocoaString {
  case storage
  case shared
  case cocoa
#if !(arch(i386) || arch(arm))
  case tagged
#endif
  
  @inline(__always)
  init(_ str: _CocoaString) {
    
#if !(arch(i386) || arch(arm))
    if _isObjCTaggedPointer(str) {
      self = .tagged
      return
    }
#endif
    
    switch _unsafeAddressOfCocoaStringClass(str) {
    case unsafeBitCast(__StringStorage.self, to: UInt.self):
      self = .storage
    case unsafeBitCast(__SharedStringStorage.self, to: UInt.self):
      self = .shared
    default:
      self = .cocoa
    }
  }
}

#if !(arch(i386) || arch(arm))
// Resiliently write a tagged _CocoaString's contents into a buffer.
@_effects(releasenone) // @opaque
internal func _bridgeTagged(
  _ cocoa: _CocoaString,
  intoUTF8 bufPtr: UnsafeMutableBufferPointer<UInt8>
) -> Int? {
  _internalInvariant(_isObjCTaggedPointer(cocoa))
  let ptr = bufPtr.baseAddress._unsafelyUnwrappedUnchecked
  let length = _stdlib_binary_CFStringGetLength(cocoa)
  _internalInvariant(length <= _SmallString.capacity)
  var count = 0
  let numCharWritten = _swift_stdlib_CFStringGetBytes(
    cocoa, _swift_shims_CFRange(location: 0, length: length),
    kCFStringEncodingUTF8, 0, 0, ptr, bufPtr.count, &count)
  return length == numCharWritten ? count : nil
}
#endif

@_effects(releasenone) // @opaque
internal func _cocoaUTF8Pointer(_ str: _CocoaString) -> UnsafePointer<UInt8>? {
  // TODO(String bridging): Is there a better interface here? This requires nul
  // termination and may assume ASCII.
  guard let ptr = _swift_stdlib_CFStringGetCStringPtr(
    str, kCFStringEncodingUTF8
  ) else { return nil }

  return ptr._asUInt8
}

private enum CocoaStringPointer {
  case ascii(UnsafePointer<UInt8>)
  case utf8(UnsafePointer<UInt8>)
  case utf16(UnsafePointer<UInt16>)
  case none
}

@_effects(readonly)
private func _getCocoaStringPointer(
  _ cfImmutableValue: _CocoaString
) -> CocoaStringPointer {
  if let utf8Ptr = _cocoaUTF8Pointer(cfImmutableValue) {
    // NOTE: CFStringGetCStringPointer means ASCII
    return .ascii(utf8Ptr)
  }
  if let utf16Ptr = _swift_stdlib_CFStringGetCharactersPtr(cfImmutableValue) {
    return .utf16(utf16Ptr)
  }
  return .none
}

@usableFromInline
@_effects(releasenone) // @opaque
internal func _bridgeCocoaString(_ cocoaString: _CocoaString) -> _StringGuts {
  switch _KnownCocoaString(cocoaString) {
  case .storage:
    return _unsafeUncheckedDowncast(
      cocoaString, to: __StringStorage.self).asString._guts
  case .shared:
    return _unsafeUncheckedDowncast(
      cocoaString, to: __SharedStringStorage.self).asString._guts
#if !(arch(i386) || arch(arm))
  case .tagged:
    return _StringGuts(_SmallString(taggedCocoa: cocoaString))
#endif
  case .cocoa:
    // "Copy" it into a value to be sure nobody will modify behind
    // our backs. In practice, when value is already immutable, this
    // just does a retain.
    //
    // TODO: Only in certain circumstances should we emit this call:
    //   1) If it's immutable, just retain it.
    //   2) If it's mutable with no associated information, then a copy must
    //      happen; might as well eagerly bridge it in.
    //   3) If it's mutable with associated information, must make the call
    let immutableCopy
      = _stdlib_binary_CFStringCreateCopy(cocoaString) as AnyObject
    
#if !(arch(i386) || arch(arm))
    if _isObjCTaggedPointer(immutableCopy) {
      return _StringGuts(_SmallString(taggedCocoa: immutableCopy))
    }
#endif
    
    let (fastUTF8, isASCII): (Bool, Bool)
    switch _getCocoaStringPointer(immutableCopy) {
    case .ascii(_): (fastUTF8, isASCII) = (true, true)
    case .utf8(_): (fastUTF8, isASCII) = (true, false)
    default:  (fastUTF8, isASCII) = (false, false)
    }
    let length = _stdlib_binary_CFStringGetLength(immutableCopy)
    
    return _StringGuts(
      cocoa: immutableCopy,
      providesFastUTF8: fastUTF8,
      isASCII: isASCII,
      length: length)
  }
}

extension String {
  public // SPI(Foundation)
  init(_cocoaString: AnyObject) {
    self._guts = _bridgeCocoaString(_cocoaString)
  }
}

extension String {
  @_effects(releasenone)
  public // SPI(Foundation)
  func _bridgeToObjectiveCImpl() -> AnyObject {
    if _guts.isSmall {
      return _guts.asSmall.withUTF8 { bufPtr in
        // TODO(String bridging): worth isASCII check for different encoding?
        return _swift_stdlib_CFStringCreateWithBytes(
            nil, bufPtr.baseAddress._unsafelyUnwrappedUnchecked,
            bufPtr.count,
            kCFStringEncodingUTF8, 0)
        as AnyObject
      }
    }
    if _guts._object.isImmortal {
      // TODO: We'd rather emit a valid ObjC object statically than create a
      // shared string class instance.
      let gutsCountAndFlags = _guts._object._countAndFlags
      return __SharedStringStorage(
        immortal: _guts._object.fastUTF8.baseAddress!,
        countAndFlags: _StringObject.CountAndFlags(
          sharedCount: _guts.count, isASCII: gutsCountAndFlags.isASCII))
    }

    _internalInvariant(_guts._object.hasObjCBridgeableObject,
      "Unknown non-bridgeable object case")
    return _guts._object.objCBridgeableObject
  }
}

// At runtime, this class is derived from `__SwiftNativeNSStringBase`,
// which is derived from `NSString`.
//
// The @_swift_native_objc_runtime_base attribute
// This allows us to subclass an Objective-C class and use the fast Swift
// memory allocator.
@objc @_swift_native_objc_runtime_base(__SwiftNativeNSStringBase)
class __SwiftNativeNSString {
  @objc internal init() {}
  deinit {}
}

// Called by the SwiftObject implementation to get the description of a value
// as an NSString.
@_silgen_name("swift_stdlib_getDescription")
public func _getDescription<T>(_ x: T) -> AnyObject {
  return String(reflecting: x)._bridgeToObjectiveCImpl()
}

#else // !_runtime(_ObjC)

internal class __SwiftNativeNSString {
  internal init() {}
  deinit {}
}

#endif

// Special-case Index <-> Offset converters for bridging and use in accelerating
// the UTF16View in general.
extension StringProtocol {
  @_specialize(where Self == String)
  @_specialize(where Self == Substring)
  public // SPI(Foundation)
  func _toUTF16Offset(_ idx: Index) -> Int {
    return self.utf16.distance(from: self.utf16.startIndex, to: idx)
  }

  @_specialize(where Self == String)
  @_specialize(where Self == Substring)
  public // SPI(Foundation)
  func _toUTF16Index(_ offset: Int) -> Index {
    return self.utf16.index(self.utf16.startIndex, offsetBy: offset)
  }

  @_specialize(where Self == String)
  @_specialize(where Self == Substring)
  public // SPI(Foundation)
  func _toUTF16Offsets(_ indices: Range<Index>) -> Range<Int> {
    let lowerbound = _toUTF16Offset(indices.lowerBound)
    let length = self.utf16.distance(
      from: indices.lowerBound, to: indices.upperBound)
    return Range(
      uncheckedBounds: (lower: lowerbound, upper: lowerbound + length))
  }

  @_specialize(where Self == String)
  @_specialize(where Self == Substring)
  public // SPI(Foundation)
  func _toUTF16Indices(_ range: Range<Int>) -> Range<Index> {
    let lowerbound = _toUTF16Index(range.lowerBound)
    let upperbound = _toUTF16Index(range.lowerBound + range.count)
    return Range(uncheckedBounds: (lower: lowerbound, upper: upperbound))
  }
}

extension String {
  public // @testable / @benchmarkable
  func _copyUTF16CodeUnits(
    into buffer: UnsafeMutableBufferPointer<UInt16>,
    range: Range<Int>
  ) {
    _internalInvariant(buffer.count >= range.count)
    let indexRange = self._toUTF16Indices(range)
    self._nativeCopyUTF16CodeUnits(into: buffer, range: indexRange)
  }
}