stdlib: SE-0065: change UnsafeBufferPointer.Indices to CountableRange<Int>

CountableRange is cheaper than DefaultRandomAccessIndices.

Author: gribozavr

stdlib/private/StdlibUnittest/StdlibUnittest.swift.gyb

@@ -329,9 +329,9 @@ public func expectSequenceType<
   X.SubSequence.SubSequence == X.SubSequence
 >(_ x: X) -> X { return x }
 
-public func expectIndexable<X : Indexable>(_ x: X) -> X { return x }
-public func expectCollectionType<
-  X : Collection
+% for Mutable in ['', 'Mutable']:
+public func expect${Mutable}CollectionType<
+  X : ${Mutable}Collection
   where
 
   // FIXME(ABI)(compiler limitation): there should be no constraints in
@@ -345,7 +345,8 @@ public func expectCollectionType<
   X.Indices.Iterator.Element == X.Index,
   X.Indices.Index == X.Index,
   X.Indices.SubSequence == X.Indices
->(_ x: X) -> X { return x }
+>(_ x: X.Type) {}
+% end
 
 /// A slice is a `Collection` that when sliced returns an instance of
 /// itself.

stdlib/public/core/UnsafeBufferPointer.swift.gyb

@@ -57,7 +57,11 @@ public struct Unsafe${Mutable}BufferPointer<Element>
     return count
   }
 
-  public typealias Indices = DefaultRandomAccessIndices<Unsafe${Mutable}BufferPointer<Element>>
+  public typealias Indices = CountableRange<Int>
+
+  public var indices: Indices {
+    return startIndex..<endIndex
+  }
 
   /// Access the `i`th element in the buffer.
   public subscript(i: Int) -> Element {

test/1_stdlib/UnsafeBufferPointer.swift.gyb renamed to validation-test/stdlib/UnsafeBufferPointer.swift.gyb

@@ -4,13 +4,28 @@
 // REQUIRES: executable_test
 
 import StdlibUnittest
+import StdlibCollectionUnittest
 
 var UnsafeBufferPointerTestSuite = TestSuite("UnsafeBufferPointer")
 var UnsafeMutableBufferPointerTestSuite = TestSuite("UnsafeMutableBufferPointer")
 
-% for (SelfName, SelfType, PointerType) in [
-%         ('UnsafeBufferPointer', 'UnsafeBufferPointer<Float>', 'UnsafePointer<Float>'),
-%         ('UnsafeMutableBufferPointer', 'UnsafeMutableBufferPointer<Float>', 'UnsafeMutablePointer<Float>')]:
+% for (SelfName, IsMutable, SelfType, PointerType) in [
+%   ('UnsafeBufferPointer', False, 'UnsafeBufferPointer<Float>', 'UnsafePointer<Float>'),
+%   ('UnsafeMutableBufferPointer', True, 'UnsafeMutableBufferPointer<Float>', 'UnsafeMutablePointer<Float>')
+% ]:
+
+${SelfName}TestSuite.test("AssociatedTypes") {
+  typealias Subject = ${SelfName}<OpaqueValue<Int>>
+  expectRandomAccessCollectionAssociatedTypes(
+    collectionType: Subject.self,
+    iteratorType: IndexingIterator<Subject>.self,
+    subSequenceType: ${'Mutable' if IsMutable else ''}RandomAccessSlice<Subject>.self,
+    indexType: Int.self,
+    indexDistanceType: Int.self,
+    indicesType: CountableRange<Int>.self)
+
+  expect${'Mutable' if IsMutable else ''}CollectionType(Subject.self)
+}
 
 ${SelfName}TestSuite.test("nilBaseAddress") {
   let emptyBuffer = ${SelfType}(start: nil, count: 0)