[Repo Assist] feat: add TaskSeq.toChannelAsync and TaskSeq.ofChannel for System.Threading.Channels integration

release-notes.txt

@@ -2,6 +2,7 @@
 Release notes:
 
 Unreleased
+    - feat: add `TaskSeq.toChannelAsync` and `TaskSeq.ofChannel` for bidirectional `System.Threading.Channels` integration, closing #415
     - test: add SideEffects module and ImmTaskSeq variant tests to TaskSeq.ChunkBy.Tests.fs, improving coverage for chunkBy and chunkByAsync
     - fixes: `Async.bind` signature corrected from `(Async<'T> -> Async<'U>)` to `('T -> Async<'U>)` to match standard monadic bind semantics (same as `Task.bind`); the previous signature made the function effectively equivalent to direct application
     - refactor: simplify splitAt 'rest' taskSeq to use while!, removing redundant go2 mutable and manual MoveNextAsync pre-advance

src/FSharp.Control.TaskSeq.Test/TaskSeq.ToXXX.Tests.fs

@@ -1,6 +1,7 @@
 module TaskSeq.Tests.``Conversion-To``
 
 open System.Collections.Generic
+open System.Threading.Channels
 
 open Xunit
 open FsUnit.Xunit
@@ -186,3 +187,72 @@ module SideEffects =
         let (results2: seq<_>) = tq |> TaskSeq.toSeq
         results1 |> Seq.toArray |> should equal [| 1..10 |]
         results2 |> Seq.toArray |> should equal [| 11..20 |]
+
+module Channel =
+
+    [<Fact>]
+    let ``TaskSeq-toChannelAsync with null writer raises`` () =
+        assertNullArg
+        <| fun () ->
+            TaskSeq.toChannelAsync null (TaskSeq.ofArray [| 1 |])
+            |> ignore
+
+    [<Fact>]
+    let ``TaskSeq-toChannelAsync with null source raises`` () =
+        let ch = Channel.CreateUnbounded<int>()
+
+        assertNullArg
+        <| fun () -> TaskSeq.toChannelAsync ch.Writer null |> ignore
+
+    [<Fact>]
+    let ``TaskSeq-ofChannel with null reader raises`` () =
+        assertNullArg
+        <| fun () -> TaskSeq.ofChannel<int> null |> ignore
+
+    [<Fact>]
+    let ``TaskSeq-toChannelAsync with empty source completes the channel`` () = task {
+        let ch = Channel.CreateUnbounded<int>()
+        do! TaskSeq.toChannelAsync ch.Writer TaskSeq.empty
+        ch.Reader.Completion.IsCompleted |> should be True
+        let! results = TaskSeq.ofChannel ch.Reader |> TaskSeq.toArrayAsync
+        results |> should be Empty
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-toChannelAsync writes all elements and completes the channel`` variant = task {
+        let tq = Gen.getSeqImmutable variant
+        let ch = Channel.CreateUnbounded<int>()
+        do! TaskSeq.toChannelAsync ch.Writer tq
+        let! results = TaskSeq.ofChannel ch.Reader |> TaskSeq.toArrayAsync
+        results |> should equal [| 1..10 |]
+        // Completion resolves once the channel is marked done and the buffer is drained
+        do! ch.Reader.Completion
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-ofChannel yields all elements written to the channel`` variant = task {
+        let tq = Gen.getSeqImmutable variant
+        let ch = Channel.CreateUnbounded<int>()
+        do! TaskSeq.toChannelAsync ch.Writer tq
+        let! results = TaskSeq.ofChannel ch.Reader |> TaskSeq.toArrayAsync
+        results |> should equal [| 1..10 |]
+    }
+
+    [<Fact>]
+    let ``TaskSeq-ofChannel ends when channel is completed and drained`` () = task {
+        let ch = Channel.CreateUnbounded<int>()
+        do! ch.Writer.WriteAsync 42
+        do! ch.Writer.WriteAsync 99
+        ch.Writer.Complete()
+        let! results = TaskSeq.ofChannel ch.Reader |> TaskSeq.toArrayAsync
+        results |> should equal [| 42; 99 |]
+    }
+
+    [<Theory; ClassData(typeof<TestSideEffectTaskSeq>)>]
+    let ``TaskSeq-toChannelAsync executes side effects`` variant = task {
+        let tq = Gen.getSeqWithSideEffect variant
+        let ch = Channel.CreateUnbounded<int>()
+        do! TaskSeq.toChannelAsync ch.Writer tq
+        let! results = TaskSeq.ofChannel ch.Reader |> TaskSeq.toArrayAsync
+        results |> should equal [| 1..10 |]
+    }

src/FSharp.Control.TaskSeq/FSharp.Control.TaskSeq.fsproj

@@ -74,5 +74,7 @@ Generates optimized IL code through resumable state machines, and comes with a c
       <!-- if using "remove unused references", this prevents FSharp.Core from being shown in that list -->
       <TreatAsUsed>true</TreatAsUsed>
     </PackageReference>
+    <!-- Provides System.Threading.Channels for netstandard2.1 consumers; built into net5.0+ -->
+    <PackageReference Include="System.Threading.Channels" Version="8.0.0" />
   </ItemGroup>
 </Project>

src/FSharp.Control.TaskSeq/TaskSeq.fs

@@ -2,6 +2,7 @@ namespace FSharp.Control
 
 open System.Collections.Generic
 open System.Threading
+open System.Threading.Channels
 open System.Threading.Tasks
 
 // Just for convenience
@@ -180,6 +181,23 @@ type TaskSeq private () =
 
     static member toIListAsync source = Internal.toResizeArrayAndMapAsync (fun x -> x :> IList<_>) source
 
+    static member toChannelAsync (writer: ChannelWriter<'T>) (source: TaskSeq<'T>) : Task =
+        Internal.checkNonNull (nameof writer) writer
+        Internal.checkNonNull (nameof source) source
+
+        task {
+            try
+                use e = source.GetAsyncEnumerator CancellationToken.None
+
+                while! e.MoveNextAsync() do
+                    do! writer.WriteAsync e.Current
+
+                writer.TryComplete() |> ignore
+            with exn ->
+                writer.TryComplete exn |> ignore
+        }
+        :> Task
+
     //
     // Convert 'OfXXX' functions
     //
@@ -261,6 +279,17 @@ type TaskSeq private () =
                 yield c
         }
 
+    static member ofChannel(reader: ChannelReader<'T>) : TaskSeq<'T> =
+        Internal.checkNonNull (nameof reader) reader
+
+        taskSeq {
+            while! reader.WaitToReadAsync() do
+                let mutable item = Unchecked.defaultof<_>
+
+                while reader.TryRead &item do
+                    yield item
+        }
+
     static member withCancellation (cancellationToken: CancellationToken) (source: TaskSeq<'T>) =
         Internal.checkNonNull (nameof source) source
 

src/FSharp.Control.TaskSeq/TaskSeq.fsi

@@ -2,6 +2,7 @@ namespace FSharp.Control
 
 open System.Collections.Generic
 open System.Threading
+open System.Threading.Channels
 open System.Threading.Tasks
 
 [<AutoOpen>]
@@ -529,6 +530,20 @@ type TaskSeq =
     /// <exception cref="T:ArgumentNullException">Thrown when the input sequence is null.</exception>
     static member toIListAsync: source: TaskSeq<'T> -> Task<IList<'T>>
 
+    /// <summary>
+    /// Writes all elements of the input task sequence <paramref name="source" /> to a
+    /// <see cref="ChannelWriter&lt;'T>" /> and marks the writer as complete when the sequence
+    /// is exhausted. If an exception is raised during iteration, the writer is completed with
+    /// that exception so that downstream readers observe it.
+    /// This function is non-blocking while it writes to the channel.
+    /// </summary>
+    ///
+    /// <param name="writer">The channel writer to write elements into.</param>
+    /// <param name="source">The input task sequence.</param>
+    /// <returns>A <see cref="Task" /> that completes when all elements have been written.</returns>
+    /// <exception cref="T:ArgumentNullException">Thrown when <paramref name="writer" /> or <paramref name="source" /> is null.</exception>
+    static member toChannelAsync: writer: ChannelWriter<'T> -> source: TaskSeq<'T> -> Task
+
     /// <summary>
     /// Views the given <see cref="array" /> as a task sequence, that is, as an <see cref="IAsyncEnumerable&lt;'T>" />.
     /// </summary>
@@ -642,6 +657,17 @@ type TaskSeq =
     /// <exception cref="T:ArgumentNullException">Thrown when the input sequence is null.</exception>
     static member ofAsyncArray: source: Async<'T> array -> TaskSeq<'T>
 
+    /// <summary>
+    /// Views a <see cref="ChannelReader&lt;'T>" /> as a task sequence. Elements are yielded as they
+    /// become available; the sequence ends when the channel is completed and all buffered elements
+    /// have been consumed.
+    /// </summary>
+    ///
+    /// <param name="reader">The channel reader to read elements from.</param>
+    /// <returns>A task sequence that yields elements from the channel.</returns>
+    /// <exception cref="T:ArgumentNullException">Thrown when <paramref name="reader" /> is null.</exception>
+    static member ofChannel: reader: ChannelReader<'T> -> TaskSeq<'T>
+
     /// <summary>
     /// Returns a task sequence that, when iterated, passes the given <paramref name="cancellationToken" /> to the
     /// underlying <see cref="IAsyncEnumerable&lt;'T&gt;" />. This is the equivalent of calling