Implement convenience factory methods for Async[Throwing]Stream (#62968)

* Implement convenience factory methods for Async[Throwing]Stream

This is the implementation for swiftlang/swift-evolution#1824

* Apply suggestions from code review

Co-authored-by: Konrad `ktoso` Malawski <konrad.malawski@project13.pl>

---------

Co-authored-by: Konrad `ktoso` Malawski <konrad.malawski@project13.pl>

Author: FranzBusch

stdlib/public/Concurrency/AsyncStream.swift

@@ -428,6 +428,27 @@ extension AsyncStream.Continuation {
   }
 }
 
+@available(SwiftStdlib 5.1, *)
+extension AsyncStream {
+  /// Initializes a new ``AsyncStream`` and an ``AsyncStream/Continuation``.
+  ///
+  /// - Parameters:
+  ///   - elementType: The element type of the stream.
+  ///   - limit: The buffering policy that the stream should use.
+  /// - Returns: A tuple containing the stream and its continuation. The continuation should be passed to the
+  /// producer while the stream should be passed to the consumer.
+  @available(SwiftStdlib 5.1, *)
+  @backDeployed(before: SwiftStdlib 5.9)
+  public static func makeStream(
+      of elementType: Element.Type = Element.self,
+      bufferingPolicy limit: Continuation.BufferingPolicy = .unbounded
+  ) -> (stream: AsyncStream<Element>, continuation: AsyncStream<Element>.Continuation) {
+    var continuation: AsyncStream<Element>.Continuation!
+    let stream = AsyncStream<Element>(bufferingPolicy: limit) { continuation = $0 }
+    return (stream: stream, continuation: continuation!)
+  }
+}
+
 @available(SwiftStdlib 5.1, *)
 extension AsyncStream: @unchecked Sendable where Element: Sendable { }
 #else

stdlib/public/Concurrency/AsyncThrowingStream.swift

@@ -473,6 +473,29 @@ extension AsyncThrowingStream.Continuation {
   }
 }
 
+@available(SwiftStdlib 5.1, *)
+extension AsyncThrowingStream {
+  /// Initializes a new ``AsyncThrowingStream`` and an ``AsyncThrowingStream/Continuation``.
+  ///
+  /// - Parameters:
+  ///   - elementType: The element type of the stream.
+  ///   - failureType: The failure type of the stream.
+  ///   - limit: The buffering policy that the stream should use.
+  /// - Returns: A tuple containing the stream and its continuation. The continuation should be passed to the
+  /// producer while the stream should be passed to the consumer.
+  @available(SwiftStdlib 5.1, *)
+  @backDeployed(before: SwiftStdlib 5.9)
+  public static func makeStream(
+      of elementType: Element.Type = Element.self,
+      throwing failureType: Failure.Type = Failure.self,
+      bufferingPolicy limit: Continuation.BufferingPolicy = .unbounded
+  ) -> (stream: AsyncThrowingStream<Element, Failure>, continuation: AsyncThrowingStream<Element, Failure>.Continuation) where Failure == Error {
+    var continuation: AsyncThrowingStream<Element, Failure>.Continuation!
+    let stream = AsyncThrowingStream<Element, Failure>(bufferingPolicy: limit) { continuation = $0 }
+    return (stream: stream, continuation: continuation!)
+  }
+}
+
 @available(SwiftStdlib 5.1, *)
 extension AsyncThrowingStream: @unchecked Sendable where Element: Sendable { }
 #else

test/Concurrency/Runtime/async_stream.swift

@@ -7,12 +7,8 @@
 // rdar://78109470
 // UNSUPPORTED: back_deployment_runtime
 
-// Race condition
-// REQUIRES: rdar78033828
-
 import _Concurrency
 import StdlibUnittest
-import Dispatch
 
 struct SomeError: Error, Equatable {
   var value = Int.random(in: 0..<100)
@@ -27,14 +23,34 @@ var tests = TestSuite("AsyncStream")
         var fulfilled = false
       }
 
+      tests.test("factory method") {
+        let (stream, continuation) = AsyncStream.makeStream(of: String.self)
+        continuation.yield("hello")
+
+        var iterator = stream.makeAsyncIterator()
+        expectEqual(await iterator.next(), "hello")
+      }
+
+      tests.test("throwing factory method") {
+        let (stream, continuation) = AsyncThrowingStream.makeStream(of: String.self, throwing: Error.self)
+        continuation.yield("hello")
+
+        var iterator = stream.makeAsyncIterator()
+        do {
+          expectEqual(try await iterator.next(), "hello")
+        } catch {
+          expectUnreachable("unexpected error thrown")
+        }
+      }
+
       tests.test("yield with no awaiting next") {
-        let series = AsyncStream(String.self) { continuation in
+        _ = AsyncStream(String.self) { continuation in
           continuation.yield("hello")
         }
       }
 
       tests.test("yield with no awaiting next throwing") {
-        let series = AsyncThrowingStream(String.self) { continuation in
+        _ = AsyncThrowingStream(String.self) { continuation in
           continuation.yield("hello")
         }
       }
@@ -122,7 +138,7 @@ var tests = TestSuite("AsyncStream")
         do {
           expectEqual(try await iterator.next(), "hello")
           expectEqual(try await iterator.next(), "world")
-          try await iterator.next()
+          _ = try await iterator.next()
           expectUnreachable("expected thrown error")
         } catch {
           if let failure = error as? SomeError {
@@ -134,15 +150,15 @@ var tests = TestSuite("AsyncStream")
       }
 
       tests.test("yield with no awaiting next detached") {
-        let series = AsyncStream(String.self) { continuation in
+        _ = AsyncStream(String.self) { continuation in
           detach {
             continuation.yield("hello")
           }
         }
       }
 
       tests.test("yield with no awaiting next detached throwing") {
-        let series = AsyncThrowingStream(String.self) { continuation in
+        _ = AsyncThrowingStream(String.self) { continuation in
           detach {
             continuation.yield("hello")
           }
@@ -246,7 +262,7 @@ var tests = TestSuite("AsyncStream")
         do {
           expectEqual(try await iterator.next(), "hello")
           expectEqual(try await iterator.next(), "world")
-          try await iterator.next()
+          _ = try await iterator.next()
           expectUnreachable("expected thrown error")
         } catch {
           if let failure = error as? SomeError {
@@ -337,7 +353,7 @@ var tests = TestSuite("AsyncStream")
         let expectation = Expectation()
 
         func scopedLifetime(_ expectation: Expectation) {
-          let series = AsyncStream(String.self) { continuation in
+          _ = AsyncStream(String.self) { continuation in
             continuation.onTermination = { @Sendable _ in expectation.fulfilled = true }
           }
         }
@@ -351,7 +367,7 @@ var tests = TestSuite("AsyncStream")
         let expectation = Expectation()
 
         func scopedLifetime(_ expectation: Expectation) {
-          let series = AsyncStream(String.self) { continuation in
+          _ = AsyncStream(String.self) { continuation in
             continuation.onTermination = { @Sendable _ in expectation.fulfilled = true }
             continuation.finish()
           }
@@ -366,7 +382,7 @@ var tests = TestSuite("AsyncStream")
         let expectation = Expectation()
 
         func scopedLifetime(_ expectation: Expectation) {
-          let series = AsyncStream(String.self) { continuation in
+          _ = AsyncStream(String.self) { continuation in
             continuation.onTermination = { @Sendable terminal in
               switch terminal {
               case .cancelled:
@@ -386,7 +402,7 @@ var tests = TestSuite("AsyncStream")
         let expectation = Expectation()
 
         func scopedLifetime(_ expectation: Expectation) {
-          let series = AsyncThrowingStream(String.self) { continuation in
+          _ = AsyncThrowingStream(String.self) { continuation in
             continuation.onTermination = { @Sendable terminal in
               switch terminal {
               case .cancelled: