[6.0🍒] NFC: Update Changelog for more porposals, and add more testing.

CHANGELOG.md

@@ -5,6 +5,26 @@
 
 ## Swift 6.0
 
+* [SE-0432][]:
+  Noncopyable enums can be pattern-matched with switches without consuming the
+  value you switch over:
+
+  ```swift
+  enum Lunch: ~Copyable {
+    case soup
+    case salad
+    case sandwich
+  }
+
+  func isSoup(_ lunch: borrowing Lunch) -> Bool {
+    switch lunch {
+      case .soup: true
+      default: false
+    }
+  }
+  ```
+
+
 * [SE-0428][]:
   Distributed actors now have the ability to support complete split server / 
   client systems, thanks to the new `@Resolvable` macro and runtime changes.
@@ -238,6 +258,24 @@ And the module structure to support such applications looks like this:
   }
   ```
 
+* [SE-0429][]:
+  The noncopyable fields of certain types can now be consumed individually:
+
+  ```swift
+  struct Token: ~Copyable {}
+
+  struct Authentication: ~Copyable {
+    let id: Token
+    let name: String
+
+    mutating func exchange(_ new: consuming Token) -> Token {
+      let old = self.id  // <- partial consumption of 'self'
+      self = .init(id: new, name: self.name)
+      return old
+    } 
+  }
+  ```
+
 * [SE-0427][]:
   You can now suppress `Copyable` on protocols, generic parameters, 
   and existentials:
@@ -10517,6 +10555,8 @@ using the `.dynamicType` member to retrieve the type of an expression should mig
 [SE-0411]: https://github.com/apple/swift-evolution/blob/main/proposals/0411-isolated-default-values.md
 [SE-0412]: https://github.com/apple/swift-evolution/blob/main/proposals/0412-strict-concurrency-for-global-variables.md
 [SE-0413]: https://github.com/apple/swift-evolution/blob/main/proposals/0413-typed-throws.md
+[SE-0429]: https://github.com/apple/swift-evolution/blob/main/proposals/0429-partial-consumption.md
+[SE-0432]: https://github.com/apple/swift-evolution/blob/main/proposals/0432-noncopyable-switch.md
 [SE-0414]: https://github.com/apple/swift-evolution/blob/main/proposals/0414-region-based-isolation.md
 [SE-0424]: https://github.com/apple/swift-evolution/blob/main/proposals/0424-custom-isolation-checking-for-serialexecutor.md
 [SE-0428]: https://github.com/apple/swift-evolution/blob/main/proposals/0428-resolve-distributed-actor-protocols.md

test/Generics/inverse_generics.swift

@@ -500,3 +500,11 @@ struct TestResolution3 {
   var dictNC: [String: NC] = [:] // expected-error {{type 'NC' does not conform to protocol 'Copyable'}}
   var exampleNC: Example<NC> = Example() // expected-error {{type 'NC' does not conform to protocol 'Copyable'}}
 }
+
+public struct Box<Wrapped: ~Copyable>: ~Copyable {}
+// Box is never copyable, so we can't support this conditional conformance.
+public enum List<Element: ~Copyable>: ~Copyable {
+  case cons(Element, Box<List<Element>>)   // expected-error {{associated value 'cons' of 'Copyable'-conforming generic enum 'List' has non-Copyable type '(Element, Box<List<Element>>)'}}
+  case empty
+}
+extension List: Copyable where Element: Copyable {}

test/Inputs/Swiftskell.swift

@@ -8,6 +8,11 @@ public protocol Show: ~Copyable {
   borrowing func show() -> String
 }
 
+extension CustomStringConvertible {
+  public func show() -> String { return description }
+}
+extension Int: Show {}
+
 public func print(_ s: borrowing some Show & ~Copyable) {
   print(s.show())
 }
@@ -50,37 +55,47 @@ public protocol Generator: ~Copyable {
   func next() -> Maybe<Element>
 }
 
+/// Eager assertion function, to avoid autoclosures.
+public func check(_ result: Bool, _ string: String? = nil,
+                  _ file: String = #file, _ line: Int = #line) {
+  if result { return }
+  var msg = "assertion failure (\(file):\(line))"
+  if let extra = string {
+    msg += ":\t" + extra
+  }
+  fatalError(msg)
+}
+
 // MARK: Tuples
 public enum Pair<L: ~Copyable, R: ~Copyable>: ~Copyable {
-  case elms(L, R)
+  case pair(L, R)
 }
+extension Pair: Copyable where L: Copyable, R: Copyable {}
 
 /// MARK: Data.Maybe
-
-public enum Maybe<Value: ~Copyable>: ~Copyable {
-  case just(Value)
+public enum Maybe<Wrapped: ~Copyable>: ~Copyable {
+  case just(Wrapped)
   case nothing
 }
-
 extension Maybe: Copyable {}
 
-extension Maybe: Show where Value: Show & ~Copyable {
+extension Maybe: Show where Wrapped: Show & ~Copyable {
   public borrowing func show() -> String {
     switch self {
-      case let .just(borrowing elm):
+      case let .just(elm):
         return elm.show()
       case .nothing:
         return "<nothing>"
     }
   }
 }
 
-extension Maybe: Eq where Value: Eq, Value: ~Copyable {
+extension Maybe: Eq where Wrapped: Eq, Wrapped: ~Copyable {
   public static func ==(_ a: borrowing Self, _ b: borrowing Self) -> Bool {
     switch a {
-      case let .just(borrowing a1):
+      case let .just(a1):
         switch b {
-          case let .just(borrowing b1):
+          case let .just(b1):
             return a1 == b1
           case .nothing:
             return false
@@ -96,19 +111,6 @@ extension Maybe: Eq where Value: Eq, Value: ~Copyable {
   }
 }
 
-
-// FIXME: triggers crash!
-// @inlinable
-// public func fromMaybe<A: ~Copyable>(_ defaultVal: consuming A, 
-//                                     _ mayb: consuming Maybe<A>) -> A {
-//   switch mayb {
-//     case let .just(payload):
-//       return payload
-//     case .nothing:
-//       return defaultVal
-//   }
-// }
-
 public func isJust<A: ~Copyable>(_ m: borrowing Maybe<A>) -> Bool {
   switch m {
     case .just:
@@ -127,3 +129,168 @@ public struct UnownedRef<Instance: AnyObject> {
   @usableFromInline
   internal unowned(unsafe) var _value: Instance
 }
+
+/// Provides underlying support so that you can create recursive enums, because
+/// noncopyable enums do not yet support indirect cases.
+public struct Box<Wrapped: ~Copyable>: ~Copyable {
+  private let _pointer: UnsafeMutablePointer<Wrapped>
+
+  init(_ wrapped: consuming Wrapped) {
+    _pointer = .allocate(capacity: 1)
+    _pointer.initialize(to: wrapped)
+  }
+
+  deinit {
+    _pointer.deinitialize(count: 1)
+    _pointer.deallocate()
+  }
+
+  consuming func take() -> Wrapped {
+    let wrapped = _pointer.move()
+    _pointer.deallocate()
+    discard self
+    return wrapped
+  }
+
+  var borrow: Wrapped {
+    _read { yield _pointer.pointee }
+  }
+
+  consuming func map(_ transform: (consuming Wrapped) -> Wrapped) -> Self {
+    _pointer.initialize(to: transform(_pointer.move()))
+    return self
+  }
+}
+
+
+/// MARK: Data.List
+///
+/// A singly-linked list
+public enum List<Element: ~Copyable>: ~Copyable {
+  case cons(Element, Box<List<Element>>)
+  case empty
+
+  public init(_ head: consuming Element,
+              _ tail: consuming List<Element>) {
+    self = .cons(head, Box(tail))
+  }
+
+  public init() { self = .empty }
+}
+
+/// Pure Iteration
+extension List where Element: ~Copyable {
+  /// Performs forward iteration through the list, accumulating a result value.
+  /// Returns f(xn,...,f(x2, f(x1, init))...), or `init` if the list is empty.
+  public borrowing func foldl<Out>(
+                        init initial: consuming Out,
+                        _ f: (borrowing Element, consuming Out) -> Out) -> Out
+                        where Out: ~Copyable {
+    func loop(_ acc: consuming Out, _ lst: borrowing Self) -> Out {
+      switch lst {
+        case .empty:
+            return acc
+        case let .cons(elm, tail):
+          return loop(f(elm, acc), tail.borrow)
+      }
+    }
+    return loop(initial, self)
+  }
+
+  /// Performs reverse iteration through the list, accumulating a result value.
+  /// Returns f(x1, f(x2,...,f(xn, init)...)) or `init` if the list is empty.
+  public borrowing func foldr<Out>(
+                        init initial: consuming Out,
+                        _ f: (borrowing Element, consuming Out) -> Out) -> Out
+                        where Out: ~Copyable {
+  switch self {
+    case .empty:
+      return initial
+    case let .cons(elm, tail):
+      return f(elm, tail.borrow.foldr(init: initial, f))
+    }
+  }
+
+  // Forward iteration without accumulating a result.
+  public borrowing func forEach(_ f: (borrowing Element) -> Void) -> Void {
+    switch self {
+    case .empty: return
+    case let .cons(elm, tail):
+      f(elm)
+      return tail.borrow.forEach(f)
+    }
+  }
+}
+
+/// Initialization
+extension List where Element: ~Copyable {
+  // Generates a list of elements [f(0), f(1), ..., f(n-1)] from left to right.
+  // For n < 0, the empty list is created.
+  public init(length n: Int, _ f: (Int) -> Element) {
+    guard n > 0 else {
+      self = .empty
+      return
+    }
+
+    let cur = n-1
+    let elm = f(cur)
+    self = List(elm, List(length: cur, f))
+  }
+}
+
+/// Basic utilities
+extension List where Element: ~Copyable {
+  /// Is this list empty?
+  ///
+  /// Complexity: O(1)
+  public var isEmpty: Bool {
+    borrowing get {
+      switch self {
+      case .empty: true
+      case .cons(_, _): false
+      }
+    }
+  }
+
+  /// How many elements are in this list?
+  ///
+  /// Complexity: O(n)
+  public borrowing func length() -> Int {
+    return foldl(init: 0) { $1 + 1 }
+  }
+
+  /// Pop the first element off the list, if present.
+  ///
+  /// Complexity: O(1)
+  public consuming func pop() -> Optional<Pair<Element, List<Element>>> {
+    switch consume self {
+      case .empty: .none
+      case let .cons(elm, tail): .pair(elm, tail.take())
+    }
+  }
+
+  /// Push an element onto the front of the list.
+  ///
+  /// Complexity: O(1)
+  public consuming func push(_ newHead: consuming Element) -> List<Element> {
+    return List(newHead, self)
+  }
+
+  /// Produces a new list that is the reverse of this list.
+  ///
+  /// Complexity: O(n)
+  public consuming func reverse() -> List<Element> {
+    var new = List<Element>()
+    while case let .pair(head, tail) = pop() {
+      new = new.push(head)
+      self = tail
+    }
+    return new
+  }
+}
+
+extension List: Show where Element: Show & ~Copyable {
+  public borrowing func show() -> String {
+    return "[" + foldl(init: "]", { $0.show() + ", " + $1 })
+  }
+}