[stdlib] Add conditional Hashable conformance for indices

Author: natecook1000

stdlib/public/core/ClosedRange.swift

@@ -85,6 +85,17 @@ extension ClosedRangeIndex : Comparable {
   }
 }
 
+extension ClosedRangeIndex : Hashable where Bound : Hashable {
+  public var hashValue: Int {
+    switch _value {
+    case .inRange(let value):
+      return value.hashValue
+    case .pastEnd:
+      return .max
+    }
+  }
+}
+
 /// A closed range that forms a collection of consecutive values.
 ///
 /// You create a `CountableClosedRange` instance by using the closed range

stdlib/public/core/DropWhile.swift.gyb

@@ -140,6 +140,12 @@ public struct LazyDropWhileIndex<Base : Collection> : Comparable {
   }
 }
 
+extension LazyDropWhileIndex : Hashable where Base.Index : Hashable {
+  public var hashValue: Int {
+    return base.hashValue
+  }
+}
+
 % for Traversal in ['Forward', 'Bidirectional']:
 %   Collection = collectionForTraversal(Traversal)
 %   Self = "LazyDropWhile" + Collection

stdlib/public/core/Flatten.swift.gyb

@@ -220,6 +220,14 @@ extension ${Index} : Comparable {
   }
 }
 
+extension ${Index} : Hashable
+  where BaseElements.Index : Hashable, BaseElements.Element.Index : Hashable
+{
+  public var hashValue: Int {
+    return _mixInt(_inner?.hashValue ?? 0) ^ _outer.hashValue
+  }
+}
+
 /// A flattened view of a base collection of collections.
 ///
 /// The elements of this view are a concatenation of the elements of

stdlib/public/core/PrefixWhile.swift.gyb

@@ -161,6 +161,17 @@ public struct LazyPrefixWhileIndex<Base : Collection> : Comparable {
   }
 }
 
+extension LazyPrefixWhileIndex : Hashable where Base.Index : Hashable {
+  public var hashValue: Int {
+    switch _value {
+    case .index(let value):
+      return value.hashValue
+    case .pastEnd:
+      return .max
+    }
+  }
+}
+
 % for Traversal in ['Forward', 'Bidirectional']:
 %   Collection = collectionForTraversal(Traversal)
 %   Self = "LazyPrefixWhile" + Collection

stdlib/public/core/Reverse.swift

@@ -149,6 +149,12 @@ public struct ReversedIndex<Base : Collection> : Comparable {
   }
 }
 
+extension ReversedIndex : Hashable where Base.Index : Hashable {
+  public var hashValue: Int {
+    return base.hashValue
+  }
+}
+
 /// A collection that presents the elements of its base collection
 /// in reverse order.
 ///
@@ -349,6 +355,12 @@ public struct ReversedRandomAccessIndex<
   }
 }
 
+extension ReversedRandomAccessIndex : Hashable where Base.Index : Hashable {
+  public var hashValue: Int {
+    return base.hashValue
+  }
+}
+
 /// A collection that presents the elements of its base collection
 /// in reverse order.
 ///

validation-test/stdlib/HashableIndices.swift

@@ -0,0 +1,38 @@
+// RUN: %target-run-simple-swift
+// REQUIRES: executable_test
+
+import StdlibUnittest
+
+var HashTests = TestSuite("HashableIndices")
+
+HashTests.test("ClosedRangeIndex") {
+  let a = 1...10
+  checkHashable(a.indices, equalityOracle: { $0 == $1 })
+}
+
+HashTests.test("FlattenIndex") {
+  let a = [1...10, 11...20, 21...30].joined()
+  checkHashable(a.indices, equalityOracle: { $0 == $1 })
+}
+
+HashTests.test("LazyDropWhileIndex") {
+  let a = (1...10).lazy.drop(while: { $0 < 5 })
+  checkHashable(a.indices, equalityOracle: { $0 == $1 })
+}
+
+HashTests.test("LazyPrefixWhileIndex") {
+  let a = (1...10).lazy.prefix(while: { $0 < 5 })
+  checkHashable(a.indices, equalityOracle: { $0 == $1 })
+}
+
+HashTests.test("ReversedIndex") {
+  let a = (1...10).lazy.filter({ $0 > 3 }).reversed()
+  checkHashable(a.indices, equalityOracle: { $0 == $1 })
+}
+
+HashTests.test("ReversedRandomAccessIndex") {
+  let a = (1...10).reversed()
+  checkHashable(a.indices, equalityOracle: { $0 == $1 })
+}
+
+runAllTests()