[stdlib] Eliminate over-constraint on StringProtocol

Author: Dave Abrahams

stdlib/public/SDK/Foundation/NSRange.swift

@@ -105,22 +105,20 @@ extension NSRange {
 //===----------------------------------------------------------------------===//
 
 extension NSRange {
-  public init<R: RangeExpression>(_ rangeExpression: R)
+  public init<R: RangeExpression>(_ region: R)
   where R.Bound: FixedWidthInteger, R.Bound.Stride : SignedInteger {
-    let range = rangeExpression.relative(to: 0..<R.Bound.max)
-    let start: Int = numericCast(range.lowerBound)
-    let end: Int = numericCast(range.upperBound)
-    self = NSRange(location: start, length: end - start)
+    let r = region.relative(to: 0..<R.Bound.max)
+    location = numericCast(r.lowerBound)
+    length = numericCast(r.count)
   }
 
-  public init<R: RangeExpression, S: StringProtocol>(_ rangeExpression: R, in string: S)
-  where R.Bound == String.Index, S.Index == String.Index {
-    let range = rangeExpression.relative(to: string)
-    let start = range.lowerBound.samePosition(in: string.utf16)
-    let end = range.upperBound.samePosition(in: string.utf16)
-    let location = string.utf16.distance(from: string.utf16.startIndex, to: start)
-    let length = string.utf16.distance(from: start, to: end)
-    self = NSRange(location: location, length: length)
+  public init<R: RangeExpression, S: StringProtocol>(_ region: R, in target: S)
+  where R.Bound == S.Index, S.Index == String.Index {
+    let r = region.relative(to: target)
+    self = NSRange(
+      location: r.lowerBound._utf16Index - target.startIndex._utf16Index,
+      length: r.upperBound._utf16Index - r.lowerBound._utf16Index
+    )
   }
 
   @available(swift, deprecated: 4, renamed: "Range.init(_:)")

stdlib/public/core/String.swift

@@ -15,22 +15,24 @@ import SwiftShims
 /// A type that can represent a string as a collection of characters.
 public protocol StringProtocol
   : RangeReplaceableCollection, BidirectionalCollection,
-  CustomDebugStringConvertible,
-  CustomReflectable, CustomPlaygroundQuickLookable,
   TextOutputStream, TextOutputStreamable,
   LosslessStringConvertible, ExpressibleByStringLiteral,
   Hashable, Comparable
   where Iterator.Element == Character {
 
-  associatedtype UTF8Index
-  var utf8: String.UTF8View { get }
-  associatedtype UTF16Index
-  var utf16: String.UTF16View { get }
-  associatedtype UnicodeScalarIndex
-  var unicodeScalars: String.UnicodeScalarView { get }
-  /*associatedtype CharacterIndex*/
-  var characters: String.CharacterView { get }
+  associatedtype UTF8View : /*Bidirectional*/Collection
+  where UTF8View.Element == UInt8 // Unicode.UTF8.CodeUnit
+  
+  associatedtype UTF16View : BidirectionalCollection
+  where UTF16View.Element == UInt16 // Unicode.UTF16.CodeUnit
 
+  associatedtype UnicodeScalarView : BidirectionalCollection
+  where UnicodeScalarView.Element == Unicode.Scalar
+  
+  var utf8: UTF8View { get }
+  var utf16: UTF16View { get }
+  var unicodeScalars: UnicodeScalarView { get }
+  
 #if _runtime(_ObjC)
   func hasPrefix(_ prefix: String) -> Bool
   func hasSuffix(_ prefix: String) -> Bool
@@ -110,6 +112,18 @@ public protocol StringProtocol
   ) rethrows -> Result
 }
 
+extension StringProtocol {
+  //@available(swift, deprecated: 3.2, obsoleted: 4.0, message: "Please use the StringProtocol itself")
+  //public var characters: Self { return self }
+
+  @available(swift, deprecated: 3.2, obsoleted: 4.0, renamed: "UTF8View.Index")
+  public typealias UTF8Index = UTF8View.Index
+  @available(swift, deprecated: 3.2, obsoleted: 4.0, renamed: "UTF16View.Index")
+  public typealias UTF16Index = UTF16View.Index
+  @available(swift, deprecated: 3.2, obsoleted: 4.0, renamed: "UnicodeScalarView.Index")
+  public typealias UnicodeScalarIndex = UnicodeScalarView.Index
+}
+
 /// A protocol that provides fast access to a known representation of String.
 ///
 /// Can be used to specialize generic functions that would otherwise end up

validation-test/compiler_crashers_2/0105-sr5050.swift

@@ -1,5 +1,8 @@
 // RUN: not --crash %target-swift-frontend %s -typecheck
 
+// See <rdar://32555384> 
+// XFAIL: *
+
 protocol P {}
 
 func bar(p: P?) {