Remove _LegacyStringCore 🎉🎉🎉

Author: lorentey

stdlib/public/core/CMakeLists.txt

@@ -125,7 +125,6 @@ set(SWIFTLIB_ESSENTIAL
   StringBridge.swift
   StringBuffer.swift
   StringComparable.swift
-  StringCore.swift
   StringGuts.swift
   StringObject.swift
   StringIndex.swift

stdlib/public/core/GroupInfo.json

@@ -15,7 +15,6 @@
     "StringBuffer.swift",
     "StringCharacterView.swift",
     "StringComparable.swift",
-    "StringCore.swift",
     "StringObject.swift",
     "StringGuts.swift",
     "StringGraphemeBreaking.swift",  

stdlib/public/core/String.swift

@@ -784,12 +784,6 @@ public struct String {
   init(_ _guts: _StringGuts) {
     self._guts = _guts
   }
-
-  public // @testable
-  var _core: _LegacyStringCore {
-    get { return _guts._legacyCore }
-    set { self._guts = _StringGuts(newValue) }
-  }
 }
 
 extension String {

stdlib/public/core/StringBridge.swift

@@ -193,40 +193,6 @@ func _makeCocoaStringGuts(_ cocoaString: _CocoaString) -> _StringGuts {
     start: start)
 }
 
-@inline(never) // Hide the CF dependency
-internal
-func makeCocoaLegacyStringCore(_cocoaString: AnyObject) -> _LegacyStringCore {
-  if let wrapped = _cocoaString as? _NSContiguousString {
-    return wrapped._core
-  }
-
-  // "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.
-  let cfImmutableValue
-    = _stdlib_binary_CFStringCreateCopy(_cocoaString) as AnyObject
-
-  let length = _swift_stdlib_CFStringGetLength(cfImmutableValue)
-
-  // Look first for null-terminated ASCII
-  // Note: the code in clownfish appears to guarantee
-  // nul-termination, but I'm waiting for an answer from Chris Kane
-  // about whether we can count on it for all time or not.
-  let nulTerminatedASCII = _swift_stdlib_CFStringGetCStringPtr(
-    cfImmutableValue, kCFStringEncodingASCII)
-
-  // start will hold the base pointer of contiguous storage, if it
-  // is found.
-  let (start, isUTF16) = _getCocoaStringPointer(cfImmutableValue)
-
-  return _LegacyStringCore(
-    baseAddress: UnsafeMutableRawPointer(mutating: start),
-    count: length,
-    elementShift: isUTF16 ? 1 : 0,
-    hasCocoaBuffer: true,
-    owner: cfImmutableValue)
-}
-
 extension String {
   public // SPI(Foundation)
   init(_cocoaString: AnyObject) {
@@ -405,11 +371,6 @@ public final class _NSContiguousString : _SwiftNativeNSString, _NSStringCore {
     }
     return try body(selfAsPointer, rhsAsPointer)
   }
-
-  public // @testable
-  var _core: _LegacyStringCore {
-    return _guts._legacyCore
-  }
 }
 
 extension String {