stdlib: move 'String : Hashable' conformance to a separate file

I'm about to add more code around it.

Author: gribozavr

stdlib/public/core/CMakeLists.txt

@@ -114,6 +114,7 @@ set(SWIFTLIB_ESSENTIAL
   StringBridge.swift
   StringBuffer.swift
   StringCore.swift
+  StringHashable.swift
   StringInterpolation.swift.gyb
   StringLegacy.swift
   StringRangeReplaceableCollection.swift.gyb

stdlib/public/core/GroupInfo.json

@@ -12,6 +12,7 @@
     "StringBuffer.swift",
     "StringCharacterView.swift",
     "StringCore.swift",
+    "StringHashable.swift",
     "StringIndexConversions.swift",
     "StringInterpolation.swift",
     "StringLegacy.swift",

stdlib/public/core/String.swift

@@ -654,52 +654,6 @@ extension String {
   }
 }
 
-#if _runtime(_ObjC)
-@_silgen_name("swift_stdlib_NSStringHashValue")
-func _stdlib_NSStringHashValue(_ str: AnyObject, _ isASCII: Bool) -> Int
-
-@_silgen_name("swift_stdlib_NSStringHashValuePointer")
-func _stdlib_NSStringHashValuePointer(_ str: OpaquePointer, _ isASCII: Bool) -> Int
-#endif
-
-extension String : Hashable {
-  /// The string's hash value.
-  ///
-  /// Hash values are not guaranteed to be equal across different executions of
-  /// your program. Do not save hash values to use during a future execution.
-  public var hashValue: Int {
-#if _runtime(_ObjC)
-    // Mix random bits into NSString's hash so that clients don't rely on
-    // Swift.String.hashValue and NSString.hash being the same.
-#if arch(i386) || arch(arm)
-    let hashOffset = Int(bitPattern: 0x88dd_cc21)
-#else
-    let hashOffset = Int(bitPattern: 0x429b_1266_88dd_cc21)
-#endif
-    // If we have a contiguous string then we can use the stack optimization.
-    let core = self._core
-    let isASCII = core.isASCII
-    if core.hasContiguousStorage {
-      let stackAllocated = _NSContiguousString(core)
-      return hashOffset ^ stackAllocated._unsafeWithNotEscapedSelfPointer {
-        return _stdlib_NSStringHashValuePointer($0, isASCII)
-      }
-    } else {
-      let cocoaString = unsafeBitCast(
-        self._bridgeToObjectiveCImpl(), to: _NSStringCore.self)
-      return hashOffset ^ _stdlib_NSStringHashValue(cocoaString, isASCII)
-    }
-#else
-    if self._core.isASCII {
-      return _swift_stdlib_unicode_hash_ascii(
-        _core.startASCII, Int32(_core.count))
-    } else {
-      return _swift_stdlib_unicode_hash(_core.startUTF16, Int32(_core.count))
-    }
-#endif
-  }
-}
-
 extension String {
   @effects(readonly)
   @_semantics("string.concat")

stdlib/public/core/StringHashable.swift

@@ -0,0 +1,60 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SwiftShims
+
+#if _runtime(_ObjC)
+@_silgen_name("swift_stdlib_NSStringHashValue")
+func _stdlib_NSStringHashValue(_ str: AnyObject, _ isASCII: Bool) -> Int
+
+@_silgen_name("swift_stdlib_NSStringHashValuePointer")
+func _stdlib_NSStringHashValuePointer(_ str: OpaquePointer, _ isASCII: Bool) -> Int
+#endif
+
+extension String : Hashable {
+  /// The string's hash value.
+  ///
+  /// Hash values are not guaranteed to be equal across different executions of
+  /// your program. Do not save hash values to use during a future execution.
+  public var hashValue: Int {
+#if _runtime(_ObjC)
+    // Mix random bits into NSString's hash so that clients don't rely on
+    // Swift.String.hashValue and NSString.hash being the same.
+#if arch(i386) || arch(arm)
+    let hashOffset = Int(bitPattern: 0x88dd_cc21)
+#else
+    let hashOffset = Int(bitPattern: 0x429b_1266_88dd_cc21)
+#endif
+    // If we have a contiguous string then we can use the stack optimization.
+    let core = self._core
+    let isASCII = core.isASCII
+    if core.hasContiguousStorage {
+      let stackAllocated = _NSContiguousString(core)
+      return hashOffset ^ stackAllocated._unsafeWithNotEscapedSelfPointer {
+        return _stdlib_NSStringHashValuePointer($0, isASCII)
+      }
+    } else {
+      let cocoaString = unsafeBitCast(
+        self._bridgeToObjectiveCImpl(), to: _NSStringCore.self)
+      return hashOffset ^ _stdlib_NSStringHashValue(cocoaString, isASCII)
+    }
+#else
+    if self._core.isASCII {
+      return _swift_stdlib_unicode_hash_ascii(
+        _core.startASCII, Int32(_core.count))
+    } else {
+      return _swift_stdlib_unicode_hash(_core.startUTF16, Int32(_core.count))
+    }
+#endif
+  }
+}
+