[Concurrency] Task revisions 3

- introduce UnsafeCurrentTask
- implement Hashable, Equatable on tasks
- assume we'll have a way to get a task from sync context
- Task.Handle now has a Failure type as well
- Task.Handle.getResult

Author: ktoso

include/swift/ABI/TaskStatus.h

@@ -25,7 +25,7 @@
 
 namespace swift {
 
-/// The abstract base class for all sttatus records.
+/// The abstract base class for all status records.
 ///
 /// TaskStatusRecords are typically allocated on the stack (possibly
 /// in the task context), partially initialized, and then atomically

stdlib/public/Concurrency/CMakeLists.txt

@@ -38,13 +38,13 @@ add_swift_target_library(swift_Concurrency ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} I
   Actor.swift
   CheckedContinuation.swift
   GlobalExecutor.cpp
+  Executor.swift
   AsyncIteratorProtocol.swift
   AsyncSequence.swift
   PartialAsyncTask.swift
   Task.cpp
   Task.swift
   TaskCancellation.swift
-  _TimeTypes.swift
   TaskAlloc.cpp
   TaskStatus.cpp
   TaskGroup.cpp

stdlib/public/Concurrency/Executor.swift

@@ -2,7 +2,7 @@
 ////
 //// This source file is part of the Swift.org open source project
 ////
-//// Copyright (c) 2020 Apple Inc. and the Swift project authors
+//// Copyright (c) 2021 Apple Inc. and the Swift project authors
 //// Licensed under Apache License v2.0 with Runtime Library Exception
 ////
 //// See https://swift.org/LICENSE.txt for license information
@@ -12,9 +12,5 @@
 
 import Swift
 
-@rethrows
-public protocol AsyncSequence {
-  associatedtype AsyncIterator: AsyncIteratorProtocol where AsyncIterator.Element == Element
-  associatedtype Element
-  func makeAsyncIterator() -> AsyncIterator
-}
+// TODO: just a placeholder; proposal and complete types soon
+public protocol ExecutorRef {}