[4.0] Add recursive where clauses to Collection protocols (#9404)

* Add Collection constraints via protocol where clauses (#9374)

* Merge pull request #9379 from airspeedswift/redundant-where

Author: airspeedswift

stdlib/private/StdlibCollectionUnittest/CheckCollectionInstance.swift.gyb

@@ -257,8 +257,7 @@ public func checkCollection<${genericParam}, C : Collection>(
   ${TRACE},
   resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
   sameValue: (${Element}, ${Element}) -> Bool
-) where C.Iterator.Element == ${Element},
-  C.SubSequence : Collection {
+) where C.Iterator.Element == ${Element} {
 
   checkForwardCollection(expected, collection, message(),
     stackTrace: stackTrace, showFrame: showFrame, file: file, line: line,
@@ -278,7 +277,6 @@ public func check${Traversal}Collection<
   resiliencyChecks: CollectionMisuseResiliencyChecks = .all
 ) where
   C.Iterator.Element == ${Element},
-  C.SubSequence : ${TraversalCollection},
   ${Element} : Equatable {
 
   check${Traversal}Collection(
@@ -298,8 +296,7 @@ public func check${Traversal}Collection<
   resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
   sameValue: (${Element}, ${Element}) -> Bool
 ) where
-  C.Iterator.Element == ${Element},
-  C.SubSequence : ${TraversalCollection} {
+  C.Iterator.Element == ${Element} {
 
   checkOneLevelOf${Traversal}Collection(expected, collection, ${trace},
     resiliencyChecks: resiliencyChecks, sameValue: sameValue)
@@ -504,8 +501,7 @@ ${genericParam}, S : ${TraversalCollection}
   resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
   sameValue: (${Element}, ${Element}) -> Bool
 ) where
-  S.Iterator.Element == ${Element},
-  S.SubSequence : ${TraversalCollection} {
+  S.Iterator.Element == ${Element} {
 
   let expectedArray = Array(expected)
 

stdlib/private/StdlibCollectionUnittest/CheckCollectionType.swift.gyb

@@ -471,16 +471,9 @@ internal enum _SubSequenceSubscriptOnRangeMode {
 %{
   from gyb_stdlib_support import collectionForTraversal
   def testConstraints(protocol):
-    if protocol == 'Collection':
-      subseq_as_collection = 'CollectionWithEquatableElement.SubSequence : Collection,'
-    else:
-      subseq_as_collection=''
     return '''
     C : %(protocol)s,
     CollectionWithEquatableElement : %(protocol)s,
-    %(subseq_as_collection)s
-    C.SubSequence : %(protocol)s,
-    C.Indices : %(protocol)s,
     CollectionWithEquatableElement.Iterator.Element : Equatable
   ''' % locals()
 
@@ -494,6 +487,7 @@ internal enum _SubSequenceSubscriptOnRangeMode {
       [CollectionWithEquatableElement.Iterator.Element]
     ) -> CollectionWithEquatableElement,
 
+
     wrapValueIntoEquatable: @escaping (
       MinimalEquatableValue) -> CollectionWithEquatableElement.Iterator.Element,
 

stdlib/private/StdlibCollectionUnittest/CheckMutableCollectionType.swift.gyb

@@ -121,8 +121,6 @@ extension TestSuite {
     isFixedLengthCollection: Bool,
     collectionIsBidirectional: Bool = false
   ) where
-    C.SubSequence : MutableCollection,
-    C.Indices : Collection,
     CollectionWithEquatableElement.Iterator.Element : Equatable,
     CollectionWithComparableElement.Iterator.Element : Comparable {
 
@@ -783,8 +781,6 @@ self.test("\(testNamePrefix).partition/InvalidOrderings") {
     withUnsafeMutableBufferPointerIsSupported: Bool,
     isFixedLengthCollection: Bool
   ) where
-    C.SubSequence : BidirectionalCollection & MutableCollection,
-    C.Indices : BidirectionalCollection,
     CollectionWithEquatableElement.Iterator.Element : Equatable,
     CollectionWithComparableElement.Iterator.Element : Comparable {
 
@@ -929,8 +925,6 @@ self.test("\(testNamePrefix).partition/DispatchesThrough_withUnsafeMutableBuffer
     withUnsafeMutableBufferPointerIsSupported: Bool,
     isFixedLengthCollection: Bool
   ) where
-    C.SubSequence : RandomAccessCollection & MutableCollection,
-    C.Indices : RandomAccessCollection,
     CollectionWithEquatableElement.Iterator.Element : Equatable,
     CollectionWithComparableElement.Iterator.Element : Comparable {
 

stdlib/private/StdlibCollectionUnittest/CheckRangeReplaceableCollectionType.swift

@@ -462,10 +462,7 @@ extension TestSuite {
     outOfBoundsIndexOffset: Int = 1,
     collectionIsBidirectional: Bool = false
   ) where
-    C.SubSequence : Collection,
-    C.Indices : Collection,
-    CollectionWithEquatableElement.Iterator.Element : Equatable,
-    CollectionWithEquatableElement.SubSequence : Collection {
+    CollectionWithEquatableElement.Iterator.Element : Equatable {
 
     var testNamePrefix = testNamePrefix
 
@@ -1180,8 +1177,6 @@ self.test("\(testNamePrefix).OperatorPlus") {
     resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
     outOfBoundsIndexOffset: Int = 1
   ) where
-    C.SubSequence : BidirectionalCollection & RangeReplaceableCollection,
-    C.Indices : BidirectionalCollection,
     CollectionWithEquatableElement.Iterator.Element : Equatable {
 
     var testNamePrefix = testNamePrefix
@@ -1302,8 +1297,6 @@ self.test("\(testNamePrefix).removeLast(n: Int)/whereIndexIsBidirectional/remove
     resiliencyChecks: CollectionMisuseResiliencyChecks = .all,
     outOfBoundsIndexOffset: Int = 1
   ) where
-    C.SubSequence : RandomAccessCollection & RangeReplaceableCollection,
-    C.Indices : RandomAccessCollection,
     CollectionWithEquatableElement.Iterator.Element : Equatable {
 
     var testNamePrefix = testNamePrefix

stdlib/private/StdlibCollectionUnittest/CheckRangeReplaceableSliceType.swift

@@ -33,7 +33,6 @@ extension TestSuite {
     collectionIsBidirectional: Bool = false
   ) where
     C.SubSequence == C,
-    C.Indices : Collection,
     CollectionWithEquatableElement.SubSequence == CollectionWithEquatableElement,
     CollectionWithEquatableElement.Iterator.Element : Equatable {
 
@@ -165,7 +164,6 @@ extension TestSuite {
     outOfBoundsIndexOffset: Int = 1
   ) where
     C.SubSequence == C,
-    C.Indices : BidirectionalCollection,
     CollectionWithEquatableElement.SubSequence == CollectionWithEquatableElement,
     CollectionWithEquatableElement.Iterator.Element : Equatable {
 
@@ -310,7 +308,6 @@ extension TestSuite {
     outOfBoundsIndexOffset: Int = 1
   ) where
     C.SubSequence == C,
-    C.Indices : RandomAccessCollection,
     CollectionWithEquatableElement.SubSequence == CollectionWithEquatableElement,
     CollectionWithEquatableElement.Iterator.Element : Equatable {
 

stdlib/private/StdlibUnittest/StdlibUnittest.swift.gyb

@@ -376,14 +376,7 @@ public func expectSequenceType<X : Sequence>(_ x: X) -> X
 % for Mutable in ['', 'Mutable']:
 public func expect${Mutable}CollectionType<X : ${Mutable}Collection>(
   _ x: X.Type
-) where
-  // FIXME(ABI)#2 (Associated Types with where clauses): there should be no constraints in
-  // the 'where' clause, all of these should be required by the protocol.
-%   if Mutable == '':
-  X.SubSequence : Collection,
-%   end
-  // X.SubSequence.Indices == X.Indices, // FIXME(ABI)#3 (Recursive Protocol Constraints): can't have this constraint now.
-  X.Indices : Collection {}
+) { }
 % end
 
 /// A slice is a `Collection` that when sliced returns an instance of
@@ -421,12 +414,7 @@ public func expectCollectionAssociatedTypes<X : Collection>(
   indexType: X.Index.Type,
   indexDistanceType: X.IndexDistance.Type,
   indicesType: X.Indices.Type
-) where
-  // FIXME(ABI)#6 (Associated Types with where clauses): there should be no constraints in
-  // the 'where' clause, all of these should be required by the protocol.
-  X.SubSequence : Collection,
-  // X.SubSequence.Indices == X.Indices, // FIXME(ABI)#7 (Recursive Protocol Constraints): can't have this constraint now.
-  X.Indices : Collection {}
+) { }
 
 /// Check that all associated types of a `BidirectionalCollection` are what we
 /// expect them to be.
@@ -437,12 +425,7 @@ public func expectBidirectionalCollectionAssociatedTypes<X : BidirectionalCollec
   indexType: X.Index.Type,
   indexDistanceType: X.IndexDistance.Type,
   indicesType: X.Indices.Type
-) where
-  // FIXME(ABI)#8 (Associated Types with where clauses): there should be no constraints in
-  // the 'where' clause, all of these should be required by the protocol.
-  X.SubSequence : BidirectionalCollection,
-  // X.SubSequence.Indices == X.Indices, // FIXME(ABI)#9 (Recursive Protocol Constraints): can't have this constraint now.
-  X.Indices : BidirectionalCollection {}
+) { }
 
 /// Check that all associated types of a `RandomAccessCollection` are what we
 /// expect them to be.
@@ -453,12 +436,7 @@ public func expectRandomAccessCollectionAssociatedTypes<X : RandomAccessCollecti
   indexType: X.Index.Type,
   indexDistanceType: X.IndexDistance.Type,
   indicesType: X.Indices.Type
-) where
-  // FIXME(ABI)#10 (Associated Types with where clauses): there should be no constraints in
-  // the 'where' clause, all of these should be required by the protocol.
-  X.SubSequence : RandomAccessCollection,
-  // X.SubSequence.Indices == X.Indices, // FIXME(ABI)#11 (Recursive Protocol Constraints): can't have this constraint now.
-  X.Indices : RandomAccessCollection {}
+) { }
 
 public struct AssertionResult : CustomStringConvertible {
   init(isPass: Bool) {

stdlib/public/core/ArrayBufferProtocol.swift

@@ -16,7 +16,7 @@
 internal protocol _ArrayBufferProtocol
   : MutableCollection, RandomAccessCollection {
 
-  associatedtype Indices : RandomAccessCollection = CountableRange<Int>
+  associatedtype Indices = CountableRange<Int>
 
   /// The type of elements stored in the buffer.
   associatedtype Element

stdlib/public/core/BidirectionalCollection.swift

@@ -65,8 +65,8 @@ public protocol _BidirectionalIndexable : _Indexable {
 ///   `c.index(before: c.index(after: i)) == i`.
 /// - If `i > c.startIndex && i <= c.endIndex`
 ///   `c.index(after: c.index(before: i)) == i`.
-public protocol BidirectionalCollection
-  : _BidirectionalIndexable, Collection {
+public protocol BidirectionalCollection : _BidirectionalIndexable, Collection 
+where SubSequence: BidirectionalCollection, Indices: BidirectionalCollection {
 
 // TODO: swift-3-indexing-model - replaces functionality in BidirectionalIndex
   /// Returns the position immediately before the given index.
@@ -84,17 +84,11 @@ public protocol BidirectionalCollection
 
   /// A sequence that can represent a contiguous subrange of the collection's
   /// elements.
-  associatedtype SubSequence : _BidirectionalIndexable, Collection
-    = BidirectionalSlice<Self>
-  // FIXME(ABI)#93 (Recursive Protocol Constraints):
-  // associatedtype SubSequence : BidirectionalCollection
+  associatedtype SubSequence = BidirectionalSlice<Self>
 
   /// A type that represents the indices that are valid for subscripting the
   /// collection, in ascending order.
-  associatedtype Indices : _BidirectionalIndexable, Collection
-    = DefaultBidirectionalIndices<Self>
-  // FIXME(ABI)#95 (Recursive Protocol Constraints):
-  // associatedtype Indices : BidirectionalCollection
+  associatedtype Indices = DefaultBidirectionalIndices<Self>
 
   /// The indices that are valid for subscripting the collection, in ascending
   /// order.

stdlib/public/core/Collection.swift

@@ -642,7 +642,10 @@ public struct IndexingIterator<
 /// forward or bidirectional collection must traverse the entire collection to
 /// count the number of contained elements, accessing its `count` property is
 /// an O(*n*) operation.
-public protocol Collection : _Indexable, Sequence {
+public protocol Collection : _Indexable, Sequence 
+where SubSequence: Collection, Indices: Collection,
+      SubSequence.Index == Index
+{
   /// A type that represents the number of steps between a pair of
   /// indices.
   associatedtype IndexDistance = Int
@@ -668,10 +671,10 @@ public protocol Collection : _Indexable, Sequence {
   /// This associated type appears as a requirement in the `Sequence`
   /// protocol, but it is restated here with stricter constraints. In a
   /// collection, the subsequence should also conform to `Collection`.
-  associatedtype SubSequence : _IndexableBase, Sequence = Slice<Self>
-      where Self.SubSequence.Index == Index,
-            Self.Iterator.Element == Self.SubSequence.Iterator.Element,
+  associatedtype SubSequence = Slice<Self>
+      where Iterator.Element == SubSequence.Iterator.Element,
             SubSequence.SubSequence == SubSequence
+
   // FIXME(ABI)#98 (Recursive Protocol Constraints):
   // FIXME(ABI)#99 (Associated Types with where clauses):
   // associatedtype SubSequence : Collection
@@ -732,10 +735,9 @@ public protocol Collection : _Indexable, Sequence {
 
   /// A type that represents the indices that are valid for subscripting the
   /// collection, in ascending order.
-  associatedtype Indices : _Indexable, Sequence = DefaultIndices<Self>
+  associatedtype Indices = DefaultIndices<Self>
     where Indices.Iterator.Element == Index,
-          Indices.Index == Index,
-          Indices.SubSequence == Indices
+          Indices.Index == Index
 
   // FIXME(ABI)#100 (Recursive Protocol Constraints):
   // associatedtype Indices : Collection

stdlib/public/core/ExistentialCollection.swift.gyb

@@ -426,14 +426,11 @@ internal class _AnyRandomAccessCollectionBox<Element>
 @_fixed_layout
 @_versioned
 internal final class _${Kind}Box<S : ${Kind}> : _Any${Kind}Box<S.Iterator.Element>
+%  if Kind == 'Sequence':
   where
   S.SubSequence : ${Kind},
-%  if Kind == 'Sequence':
   S.SubSequence.Iterator.Element == S.Iterator.Element,
   S.SubSequence.SubSequence == S.SubSequence
-%  else:
-  S.SubSequence.Indices : ${Kind},
-  S.Indices : ${Kind}
 %  end
 {
   internal typealias Element = S.Iterator.Element
@@ -1040,10 +1037,7 @@ public struct ${Self}<Element>
     where
     // FIXME(ABI)#101 (Associated Types with where clauses): these constraints should be applied to
     // associated types of Collection.
-    C.SubSequence : ${SubProtocol},
-    C.SubSequence.Iterator.Element == Element,
-    C.SubSequence.Indices : ${SubProtocol},
-    C.Indices : ${SubProtocol}
+    C.SubSequence.Iterator.Element == Element
      {
     // Traversal: ${Traversal}
     // SubTraversal: ${SubTraversal}

stdlib/public/core/Mirror.swift

@@ -214,13 +214,7 @@ public struct Mirror {
     children: C,
     displayStyle: DisplayStyle? = nil,
     ancestorRepresentation: AncestorRepresentation = .generated
-  ) where
-    C.Iterator.Element == Child,
-    // FIXME(ABI)#47 (Associated Types with where clauses): these constraints should be applied to
-    // associated types of Collection.
-    C.SubSequence : Collection,
-    C.SubSequence.Indices : Collection,
-    C.Indices : Collection {
+  ) where C.Iterator.Element == Child {
 
     self.subjectType = Subject.self
     self._makeSuperclassMirror = Mirror._superclassIterator(
@@ -267,11 +261,7 @@ public struct Mirror {
     unlabeledChildren: C,
     displayStyle: DisplayStyle? = nil,
     ancestorRepresentation: AncestorRepresentation = .generated
-  ) where
-    // FIXME(ABI)#48 (Associated Types with where clauses): these constraints should be applied to
-    // associated types of Collection.
-    C.SubSequence : Collection,
-    C.Indices : Collection {
+  ) {
 
     self.subjectType = Subject.self
     self._makeSuperclassMirror = Mirror._superclassIterator(

stdlib/public/core/MutableCollection.swift

@@ -217,14 +217,9 @@ public protocol _MutableIndexable : _Indexable {
 ///     // Must be equivalent to:
 ///     a[i] = x
 ///     let y = x
-public protocol MutableCollection : _MutableIndexable, Collection {
-  // FIXME(ABI)#181: should be constrained to MutableCollection
-  // (<rdar://problem/20715009> Implement recursive protocol
-  // constraints)
-  /// A collection that represents a contiguous subrange of the collection's
-  /// elements.
-  associatedtype SubSequence : Collection /*: MutableCollection*/
-    = MutableSlice<Self>
+public protocol MutableCollection : _MutableIndexable, Collection
+where SubSequence: MutableCollection {
+  associatedtype SubSequence = MutableSlice<Self>
 
   /// Accesses the element at the specified position.
   ///

stdlib/public/core/RandomAccessCollection.swift

@@ -48,20 +48,15 @@ public protocol _RandomAccessIndexable : _BidirectionalIndexable {
 /// `distance(from:to:)` methods with O(1) efficiency.
 public protocol RandomAccessCollection :
   _RandomAccessIndexable, BidirectionalCollection
+  where SubSequence: RandomAccessCollection, Indices: RandomAccessCollection
 {
   /// A collection that represents a contiguous subrange of the collection's
   /// elements.
-  associatedtype SubSequence : _RandomAccessIndexable, BidirectionalCollection
-    = RandomAccessSlice<Self>
-  // FIXME(ABI)#102 (Recursive Protocol Constraints):
-  // associatedtype SubSequence : RandomAccessCollection
+  associatedtype SubSequence = RandomAccessSlice<Self>
 
   /// A type that represents the indices that are valid for subscripting the
   /// collection, in ascending order.
-  associatedtype Indices : _RandomAccessIndexable, BidirectionalCollection
-    = DefaultRandomAccessIndices<Self>
-  // FIXME(ABI)#103 (Recursive Protocol Constraints):
-  // associatedtype Indices : RandomAccessCollection
+  associatedtype Indices = DefaultRandomAccessIndices<Self>
 
   /// The indices that are valid for subscripting the collection, in ascending
   /// order.

validation-test/stdlib/CollectionDiagnostics.swift

@@ -23,7 +23,7 @@ struct CollectionWithBadSubSequence : Collection {
     fatalError("unreachable")
   }
 
-  // expected-note@+3 {{possibly intended match 'CollectionWithBadSubSequence.SubSequence' (aka 'OpaqueValue<Int8>') does not conform to 'Sequence'}}
+  // expected-note@+3 {{possibly intended match}}
   // expected-note@+2 {{possibly intended match}}
   // expected-note@+1 {{possibly intended match}}
   typealias SubSequence = OpaqueValue<Int8>