[5.4] Revert lazy children improvement in Swift Mirror

stdlib/public/core/CMakeLists.txt

@@ -60,7 +60,6 @@ set(SWIFTLIB_ESSENTIAL
   DictionaryVariant.swift
   DropWhile.swift
   Dump.swift
-  EitherSequence.swift
   EmptyCollection.swift
   Equatable.swift
   ErrorType.swift

stdlib/public/core/DebuggerSupport.swift

@@ -110,7 +110,7 @@ public enum _DebuggerSupport {
 
   private static func ivarCount(mirror: Mirror) -> Int {
     let ivars = mirror.superclassMirror.map(ivarCount) ?? 0
-    return ivars + mirror._children.count
+    return ivars + mirror.children.count
   }
 
   private static func shouldExpand(
@@ -119,7 +119,7 @@ public enum _DebuggerSupport {
     isRoot: Bool
   ) -> Bool {
     if isRoot || collectionStatus.isCollection { return true }
-    if !mirror._children.isEmpty { return true }
+    if !mirror.children.isEmpty { return true }
     if mirror.displayStyle == .`class` { return true }
     if let sc = mirror.superclassMirror { return ivarCount(mirror: sc) > 0 }
     return true
@@ -161,7 +161,7 @@ public enum _DebuggerSupport {
     }
     let willExpand = isNonClass || isCustomReflectable
 
-    let count = mirror._children.count
+    let count = mirror.children.count
     let bullet = isRoot && (count == 0 || !willExpand) ? ""
       : count == 0    ? "- "
       : maxDepth <= 0 ? "▹ " : "▿ "
@@ -209,7 +209,7 @@ public enum _DebuggerSupport {
         target: &target)
     }
 
-    for (optionalName,child) in mirror._children {
+    for (optionalName,child) in mirror.children {
       let childName = optionalName ?? "\(printedElements)"
       if maxItemCounter <= 0 {
         print(String(repeating: " ", count: indent+4), terminator: "", to: &target)

stdlib/public/core/Dump.swift

@@ -99,7 +99,7 @@ internal func _dump_unlocked<TargetStream: TextOutputStream>(
   for _ in 0..<indent { target.write(" ") }
 
   let mirror = Mirror(reflecting: value)
-  let count = mirror._children.count
+  let count = mirror.children.count
   let bullet = count == 0    ? "-"
              : maxDepth <= 0 ? "▹" : "▿"
   target.write(bullet)
@@ -149,7 +149,7 @@ internal func _dump_unlocked<TargetStream: TextOutputStream>(
       visitedItems: &visitedItems)
   }
 
-  var currentIndex = mirror._children.startIndex
+  var currentIndex = mirror.children.startIndex
   for i in 0..<count {
     if maxItemCounter <= 0 {
       for _ in 0..<(indent+4) {
@@ -167,8 +167,8 @@ internal func _dump_unlocked<TargetStream: TextOutputStream>(
       return
     }
 
-    let (name, child) = mirror._children[currentIndex]
-    mirror._children.formIndex(after: &currentIndex)
+    let (name, child) = mirror.children[currentIndex]
+    mirror.children.formIndex(after: &currentIndex)
     _dump_unlocked(
       child,
       to: &target,
@@ -196,7 +196,7 @@ internal func _dumpSuperclass_unlocked<TargetStream: TextOutputStream>(
 
   for _ in 0..<indent { target.write(" ") }
 
-  let count = mirror._children.count
+  let count = mirror.children.count
   let bullet = count == 0    ? "-"
              : maxDepth <= 0 ? "▹" : "▿"
   target.write(bullet)
@@ -216,7 +216,7 @@ internal func _dumpSuperclass_unlocked<TargetStream: TextOutputStream>(
       visitedItems: &visitedItems)
   }
 
-  var currentIndex = mirror._children.startIndex
+  var currentIndex = mirror.children.startIndex
   for i in 0..<count {
     if maxItemCounter <= 0 {
       for _ in 0..<(indent+4) {
@@ -234,8 +234,8 @@ internal func _dumpSuperclass_unlocked<TargetStream: TextOutputStream>(
       return
     }
 
-    let (name, child) = mirror._children[currentIndex]
-    mirror._children.formIndex(after: &currentIndex)
+    let (name, child) = mirror.children[currentIndex]
+    mirror.children.formIndex(after: &currentIndex)
     _dump_unlocked(
       child,
       to: &target,

stdlib/public/core/GroupInfo.json

@@ -64,7 +64,6 @@
     "RandomAccessCollection.swift",
     "MutableCollection.swift",
     "CollectionAlgorithms.swift",
-    "EitherSequence.swift",
     "EmptyCollection.swift",
     "Stride.swift",
     "Repeat.swift",

stdlib/public/core/Mirror.swift

@@ -100,13 +100,25 @@ public struct Mirror {
     /// `superclassMirror` property is `nil`.
     case suppressed
   }
-
 
-  /// The static type of the subject being reflected.
+  /// Creates a mirror that reflects on the given instance.
   ///
-  /// This type may differ from the subject's dynamic type when this mirror
-  /// is the `superclassMirror` of another mirror.
-  public let subjectType: Any.Type
+  /// If the dynamic type of `subject` conforms to `CustomReflectable`, the
+  /// resulting mirror is determined by its `customMirror` property.
+  /// Otherwise, the result is generated by the language.
+  ///
+  /// If the dynamic type of `subject` has value semantics, subsequent
+  /// mutations of `subject` will not observable in `Mirror`.  In general,
+  /// though, the observability of mutations is unspecified.
+  ///
+  /// - Parameter subject: The instance for which to create a mirror.
+  public init(reflecting subject: Any) {
+    if case let customized as CustomReflectable = subject {
+      self = customized.customMirror
+    } else {
+      self = Mirror(internalReflecting: subject)
+    }
+  }
 
   /// An element of the reflected instance's structure.
   ///
@@ -130,26 +142,6 @@ public struct Mirror {
   ///     }
   public typealias Children = AnyCollection<Child>
 
-  internal typealias _Children
-    = _EitherCollection<ReflectedChildren,AnyCollection<Child>>
-
-  internal var _children: _Children
-
-  /// A collection of `Child` elements describing the structure of the
-  /// reflected subject.
-  public var children: Children { AnyCollection(_children) }
-
-  /// A suggested display style for the reflected subject.
-  public let displayStyle: DisplayStyle?
-
-  /// A mirror of the subject's superclass, if one exists.
-  public var superclassMirror: Mirror? {
-    return _makeSuperclassMirror()
-  }
-
-  internal let _makeSuperclassMirror: () -> Mirror?
-  internal let _defaultDescendantRepresentation: _DefaultDescendantRepresentation
-
   /// A suggestion of how a mirror's subject is to be interpreted.
   ///
   /// Playgrounds and the debugger will show a representation similar
@@ -160,25 +152,6 @@ public struct Mirror {
     case dictionary, `set`
   }
 
-  /// Creates a mirror that reflects on the given instance.
-  ///
-  /// If the dynamic type of `subject` conforms to `CustomReflectable`, the
-  /// resulting mirror is determined by its `customMirror` property.
-  /// Otherwise, the result is generated by the language.
-  ///
-  /// If the dynamic type of `subject` has value semantics, subsequent
-  /// mutations of `subject` will not observable in `Mirror`.  In general,
-  /// though, the observability of mutations is unspecified.
-  ///
-  /// - Parameter subject: The instance for which to create a mirror.
-  public init(reflecting subject: Any) {
-    if case let customized as CustomReflectable = subject {
-      self = customized.customMirror
-    } else {
-      self = Mirror(internalReflecting: subject)
-    }
-  }
-
   internal static func _noSuperclassMirror() -> Mirror? { return nil }
 
   @_semantics("optimize.sil.specialize.generic.never")
@@ -250,7 +223,7 @@ public struct Mirror {
     self._makeSuperclassMirror = Mirror._superclassIterator(
       subject, ancestorRepresentation)
 
-    self._children = _Children(children)
+    self.children = Children(children)
     self.displayStyle = displayStyle
     self._defaultDescendantRepresentation
       = subject is CustomLeafReflectable ? .suppressed : .generated
@@ -295,7 +268,7 @@ public struct Mirror {
 
     let lazyChildren =
       unlabeledChildren.lazy.map { Child(label: nil, value: $0) }
-    self._children = _Children(lazyChildren)
+    self.children = Children(lazyChildren)
 
     self.displayStyle = displayStyle
     self._defaultDescendantRepresentation
@@ -342,12 +315,33 @@ public struct Mirror {
       subject, ancestorRepresentation)
 
     let lazyChildren = children.lazy.map { Child(label: $0.0, value: $0.1) }
-    self._children = _Children(lazyChildren)
+    self.children = Children(lazyChildren)
 
     self.displayStyle = displayStyle
     self._defaultDescendantRepresentation
       = subject is CustomLeafReflectable ? .suppressed : .generated
   }
+
+  /// The static type of the subject being reflected.
+  ///
+  /// This type may differ from the subject's dynamic type when this mirror
+  /// is the `superclassMirror` of another mirror.
+  public let subjectType: Any.Type
+
+  /// A collection of `Child` elements describing the structure of the
+  /// reflected subject.
+  public let children: Children
+
+  /// A suggested display style for the reflected subject.
+  public let displayStyle: DisplayStyle?
+
+  /// A mirror of the subject's superclass, if one exists.
+  public var superclassMirror: Mirror? {
+    return _makeSuperclassMirror()
+  }
+
+  internal let _makeSuperclassMirror: () -> Mirror?
+  internal let _defaultDescendantRepresentation: _DefaultDescendantRepresentation
 }
 
 /// A type that explicitly supplies its own mirror.
@@ -384,6 +378,14 @@ extension Int: MirrorPath {}
 extension String: MirrorPath {}
 
 extension Mirror {
+  internal struct _Dummy: CustomReflectable {
+      internal init(mirror: Mirror) {
+      self.mirror = mirror
+    }
+    internal var mirror: Mirror
+    internal var customMirror: Mirror { return mirror }
+  }
+
   /// Returns a specific descendant of the reflected subject, or `nil` if no
   /// such descendant exists.
   ///
@@ -431,28 +433,24 @@ extension Mirror {
   public func descendant(
     _ first: MirrorPath, _ rest: MirrorPath...
   ) -> Any? {
-
-    func fetch(_ path: MirrorPath, in children: _Children) -> Any? {
-      let position: _Children.Index?
-      switch path {
-      case let label as String:
-        position = children.firstIndex { $0.label == label }
-      case let offset as Int:
+    var result: Any = _Dummy(mirror: self)
+    for e in [first] + rest {
+      let children = Mirror(reflecting: result).children
+      let position: Children.Index
+      if case let label as String = e {
+        position = children.firstIndex { $0.label == label } ?? children.endIndex
+      }
+      else if let offset = e as? Int {
         position = children.index(children.startIndex,
           offsetBy: offset,
-          limitedBy: children.endIndex)
-      default:
+          limitedBy: children.endIndex) ?? children.endIndex
+      }
+      else {
         _preconditionFailure(
           "Someone added a conformance to MirrorPath; that privilege is reserved to the standard library")
       }
-      return position.map { children[$0].value }
-    }
-
-    guard var result = fetch(first, in: _children) else { return nil }
-    for path in rest {
-      guard let next = fetch(path, in: Mirror(reflecting: result)._children)
-        else { return nil }
-      result = next
+      if position == children.endIndex { return nil }
+      result = children[position].value
     }
     return result
   }

stdlib/public/core/OutputStream.swift

@@ -290,15 +290,15 @@ internal func _adHocPrint_unlocked<T, TargetStream: TextOutputStream>(
   if let displayStyle = mirror.displayStyle {
     switch displayStyle {
       case .optional:
-        if let child = mirror._children.first {
+        if let child = mirror.children.first {
           _debugPrint_unlocked(child.1, &target)
         } else {
           _debugPrint_unlocked("nil", &target)
         }
       case .tuple:
         target.write("(")
         var first = true
-        for (label, value) in mirror._children {
+        for (label, value) in mirror.children {
           if first {
             first = false
           } else {
@@ -319,7 +319,7 @@ internal func _adHocPrint_unlocked<T, TargetStream: TextOutputStream>(
         printTypeName(mirror.subjectType)
         target.write("(")
         var first = true
-        for (label, value) in mirror._children {
+        for (label, value) in mirror.children {
           if let label = label {
             if first {
               first = false
@@ -345,7 +345,7 @@ internal func _adHocPrint_unlocked<T, TargetStream: TextOutputStream>(
           // If the case name is garbage, just print the type name.
           printTypeName(mirror.subjectType)
         }
-        if let (_, value) = mirror._children.first {
+        if let (_, value) = mirror.children.first {
           if Mirror(reflecting: value).displayStyle == .tuple {
             _debugPrint_unlocked(value, &target)
           } else {
@@ -450,19 +450,19 @@ internal func _dumpPrint_unlocked<T, TargetStream: TextOutputStream>(
     // count
     switch displayStyle {
     case .tuple:
-      let count = mirror._children.count
+      let count = mirror.children.count
       target.write(count == 1 ? "(1 element)" : "(\(count) elements)")
       return
     case .collection:
-      let count = mirror._children.count
+      let count = mirror.children.count
       target.write(count == 1 ? "1 element" : "\(count) elements")
       return
     case .dictionary:
-      let count = mirror._children.count
+      let count = mirror.children.count
       target.write(count == 1 ? "1 key/value pair" : "\(count) key/value pairs")
       return
     case .`set`:
-      let count = mirror._children.count
+      let count = mirror.children.count
       target.write(count == 1 ? "1 member" : "\(count) members")
       return
     default:

stdlib/public/core/ReflectionMirror.swift

@@ -128,25 +128,17 @@ internal func _getClassPlaygroundQuickLook(
 #endif
 
 extension Mirror {
-  internal struct ReflectedChildren: RandomAccessCollection {
-    let subject: Any
-    let subjectType: Any.Type
-    var startIndex: Int { 0 }
-    var endIndex: Int { _getChildCount(subject, type: subjectType) }
-    subscript(index: Int) -> Child {
-      getChild(of: subject, type: subjectType, index: index)
-    }
-  }
-
-  internal init(
-    internalReflecting subject: Any,
-    subjectType: Any.Type? = nil,
-    customAncestor: Mirror? = nil
-  ) {
+  internal init(internalReflecting subject: Any,
+              subjectType: Any.Type? = nil,
+              customAncestor: Mirror? = nil)
+  {
     let subjectType = subjectType ?? _getNormalizedType(subject, type: type(of: subject))
 
-    self._children = _Children(
-      ReflectedChildren(subject: subject, subjectType: subjectType))
+    let childCount = _getChildCount(subject, type: subjectType)
+    let children = (0 ..< childCount).lazy.map({
+      getChild(of: subject, type: subjectType, index: $0)
+    })
+    self.children = Children(children)
 
     self._makeSuperclassMirror = {
       guard let subjectClass = subjectType as? AnyClass,