[Stdlib] For Collections, the SubSequence of a Subsequence is SubSequence

lib/AST/GenericSignatureBuilder.cpp

@@ -4211,6 +4211,15 @@ static void computeDerivedSameTypeComponents(
     assert(componentOf.count(concrete.archetype) > 0);
     auto &component = components[componentOf[concrete.archetype]];
 
+    // FIXME: Skip self-derived sources. This means our attempts to "stage"
+    // construction of self-derived sources really don't work, because we
+    // discover more information later, so we need a more on-line or
+    // iterative approach.
+    bool derivedViaConcrete;
+    if (concrete.source->isSelfDerivedSource(concrete.archetype,
+                                             derivedViaConcrete))
+      continue;
+
     // If it has a better source than we'd seen before for this component,
     // keep it.
     auto &bestConcreteTypeSource = component.concreteTypeSource;

stdlib/private/StdlibCollectionUnittest/CheckCollectionType.swift.gyb

@@ -480,7 +480,6 @@ internal enum _SubSequenceSubscriptOnRangeMode {
     CollectionWithEquatableElement : %(protocol)s,
     %(subseq_as_collection)s
     C.SubSequence : %(protocol)s,
-    C.SubSequence.SubSequence == C.SubSequence,
     C.Indices : %(protocol)s,
     CollectionWithEquatableElement.Iterator.Element : Equatable
   ''' % locals()

stdlib/private/StdlibCollectionUnittest/CheckMutableCollectionType.swift.gyb

@@ -122,7 +122,6 @@ extension TestSuite {
     collectionIsBidirectional: Bool = false
   ) where
     C.SubSequence : MutableCollection,
-    C.SubSequence.SubSequence == C.SubSequence,
     C.Indices : Collection,
     CollectionWithEquatableElement.Iterator.Element : Equatable,
     CollectionWithComparableElement.Iterator.Element : Comparable {
@@ -785,7 +784,6 @@ self.test("\(testNamePrefix).partition/InvalidOrderings") {
     isFixedLengthCollection: Bool
   ) where
     C.SubSequence : BidirectionalCollection & MutableCollection,
-    C.SubSequence.SubSequence == C.SubSequence,
     C.Indices : BidirectionalCollection,
     CollectionWithEquatableElement.Iterator.Element : Equatable,
     CollectionWithComparableElement.Iterator.Element : Comparable {
@@ -932,7 +930,6 @@ self.test("\(testNamePrefix).partition/DispatchesThrough_withUnsafeMutableBuffer
     isFixedLengthCollection: Bool
   ) where
     C.SubSequence : RandomAccessCollection & MutableCollection,
-    C.SubSequence.SubSequence == C.SubSequence,
     C.Indices : RandomAccessCollection,
     CollectionWithEquatableElement.Iterator.Element : Equatable,
     CollectionWithComparableElement.Iterator.Element : Comparable {

stdlib/private/StdlibCollectionUnittest/CheckRangeReplaceableCollectionType.swift

@@ -463,7 +463,6 @@ extension TestSuite {
     collectionIsBidirectional: Bool = false
   ) where
     C.SubSequence : Collection,
-    C.SubSequence.SubSequence == C.SubSequence,
     C.Indices : Collection,
     CollectionWithEquatableElement.Iterator.Element : Equatable,
     CollectionWithEquatableElement.SubSequence : Collection {
@@ -1182,7 +1181,6 @@ self.test("\(testNamePrefix).OperatorPlus") {
     outOfBoundsIndexOffset: Int = 1
   ) where
     C.SubSequence : BidirectionalCollection & RangeReplaceableCollection,
-    C.SubSequence.SubSequence == C.SubSequence,
     C.Indices : BidirectionalCollection,
     CollectionWithEquatableElement.Iterator.Element : Equatable {
 
@@ -1305,7 +1303,6 @@ self.test("\(testNamePrefix).removeLast(n: Int)/whereIndexIsBidirectional/remove
     outOfBoundsIndexOffset: Int = 1
   ) where
     C.SubSequence : RandomAccessCollection & RangeReplaceableCollection,
-    C.SubSequence.SubSequence == C.SubSequence,
     C.Indices : RandomAccessCollection,
     CollectionWithEquatableElement.Iterator.Element : Equatable {
 

stdlib/private/StdlibUnittest/StdlibUnittest.swift.gyb

@@ -367,7 +367,6 @@ public func expect${Mutable}CollectionType<X : ${Mutable}Collection>(
   X.SubSequence : Collection,
 %   end
   // X.SubSequence.Indices == X.Indices, // FIXME(ABI)#3 (Recursive Protocol Constraints): can't have this constraint now.
-  X.SubSequence.SubSequence == X.SubSequence,
   X.Indices : Collection {}
 % end
 
@@ -411,7 +410,6 @@ public func expectCollectionAssociatedTypes<X : Collection>(
   // 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.SubSequence.SubSequence == X.SubSequence,
   X.Indices : Collection {}
 
 /// Check that all associated types of a `BidirectionalCollection` are what we
@@ -428,7 +426,6 @@ public func expectBidirectionalCollectionAssociatedTypes<X : BidirectionalCollec
   // 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.SubSequence.SubSequence == X.SubSequence,
   X.Indices : BidirectionalCollection {}
 
 /// Check that all associated types of a `RandomAccessCollection` are what we
@@ -445,7 +442,6 @@ public func expectRandomAccessCollectionAssociatedTypes<X : RandomAccessCollecti
   // 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.SubSequence.SubSequence == X.SubSequence,
   X.Indices : RandomAccessCollection {}
 
 public struct AssertionResult : CustomStringConvertible {

stdlib/public/core/Collection.swift

@@ -662,14 +662,13 @@ public protocol Collection : _Indexable, Sequence {
   /// 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
+            Self.Iterator.Element == Self.SubSequence.Iterator.Element,
+            SubSequence.SubSequence == SubSequence
   // FIXME(ABI)#98 (Recursive Protocol Constraints):
   // FIXME(ABI)#99 (Associated Types with where clauses):
   // associatedtype SubSequence : Collection
   //   where
-  //   ,
   //   SubSequence.Indices == Indices,
-  //   SubSequence.SubSequence == SubSequence
   //
   // (<rdar://problem/20715009> Implement recursive protocol
   // constraints)

stdlib/public/core/ExistentialCollection.swift.gyb

@@ -430,13 +430,11 @@ internal final class _${Kind}Box<S : ${Kind}> : _Any${Kind}Box<S.Iterator.Elemen
   S.SubSequence : ${Kind},
 %  if Kind == 'Sequence':
   S.SubSequence.Iterator.Element == S.Iterator.Element,
-%end
   S.SubSequence.SubSequence == S.SubSequence
-%   if Kind != 'Sequence':
-  ,
+%  else:
   S.SubSequence.Indices : ${Kind},
   S.Indices : ${Kind}
-%   end
+%  end
 {
   internal typealias Element = S.Iterator.Element
 
@@ -1045,7 +1043,6 @@ public struct ${Self}<Element>
     C.SubSequence : ${SubProtocol},
     C.SubSequence.Iterator.Element == Element,
     C.SubSequence.Indices : ${SubProtocol},
-    C.SubSequence.SubSequence == C.SubSequence,
     C.Indices : ${SubProtocol}
      {
     // Traversal: ${Traversal}

stdlib/public/core/LazyCollection.swift.gyb

@@ -163,8 +163,8 @@ extension ${Self} : ${TraversalCollection} {
   ///
   /// - Complexity: O(1)
   @_inlineable
-  public subscript(bounds: Range<Index>) -> ${Self}<${Slice}<Base>> {
-    return ${Slice}(base: _base, bounds: bounds).lazy
+  public subscript(bounds: Range<Index>) -> ${Slice}<${Self}<Base>> {
+    return ${Slice}(base: self, bounds: bounds)
   }
 
   /// A Boolean value indicating whether the collection is empty.

stdlib/public/core/Mirror.swift

@@ -220,7 +220,6 @@ public struct Mirror {
     // associated types of Collection.
     C.SubSequence : Collection,
     C.SubSequence.Indices : Collection,
-    C.SubSequence.SubSequence == C.SubSequence,
     C.Indices : Collection {
 
     self.subjectType = Subject.self
@@ -272,7 +271,6 @@ public struct Mirror {
     // FIXME(ABI)#48 (Associated Types with where clauses): these constraints should be applied to
     // associated types of Collection.
     C.SubSequence : Collection,
-    C.SubSequence.SubSequence == C.SubSequence,
     C.Indices : Collection {
 
     self.subjectType = Subject.self