From c322b873ed9828fcb010863b0ce63e6358778524 Mon Sep 17 00:00:00 2001
From: Fraser Waters <frassle@gmail.com>
Date: Thu, 29 Aug 2019 18:07:03 +0100
Subject: [PATCH 1/2] Change cancellation test to not depend on how AwaitTask
 works

This test is to check that when an Async is started as a Task (via
StartAsTask) that when cancelled the Task isn't immediately marked as
cancelled but instead waits for the underlying Async to finish (normally
via cancellation)
---
 .../Microsoft.FSharp.Control/AsyncType.fs            | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/AsyncType.fs b/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/AsyncType.fs
index c0797038f56..100ea0b6922 100644
--- a/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/AsyncType.fs
+++ b/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/AsyncType.fs
@@ -145,10 +145,12 @@ type AsyncType() =
     [<Test>]
     member this.StartAsTaskCancellation () =
         let cts = new CancellationTokenSource()
-        let tcs = TaskCompletionSource<unit>()
+        let mutable spinloop = true
+        let doSpinloop () = while spinloop do ()
         let a = async {
             cts.CancelAfter (100)
-            do! tcs.Task |> Async.AwaitTask }
+            doSpinloop()
+        }        
 #if !NET46
         let t : Task<unit> =
 #else
@@ -156,13 +158,13 @@ type AsyncType() =
 #endif
             Async.StartAsTask(a, cancellationToken = cts.Token)
 
-        // Should not finish
+        // Should not finish, we don't eagerly mark the task done just because it's been signaled to cancel.
         try
             let result = t.Wait(300)
             Assert.IsFalse (result)
-        with :? AggregateException -> Assert.Fail "Task should not finish, jet"
+        with :? AggregateException -> Assert.Fail "Task should not finish, yet"
 
-        tcs.SetCanceled()
+        spinloop <- false
         
         try
             this.WaitASec t

From 75500f176803b4f4f370313d59f8f0c2375d66ff Mon Sep 17 00:00:00 2001
From: Fraser Waters <frassle@gmail.com>
Date: Thu, 29 Aug 2019 19:29:20 +0100
Subject: [PATCH 2/2] Add test that AwaitTask ignore async cancellation

---
 .../Microsoft.FSharp.Control/AsyncType.fs     | 27 ++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/AsyncType.fs b/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/AsyncType.fs
index 100ea0b6922..79a179bea1e 100644
--- a/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/AsyncType.fs
+++ b/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/AsyncType.fs
@@ -150,7 +150,7 @@ type AsyncType() =
         let a = async {
             cts.CancelAfter (100)
             doSpinloop()
-        }        
+        }
 #if !NET46
         let t : Task<unit> =
 #else
@@ -174,6 +174,31 @@ type AsyncType() =
             | _ -> reraise()
         Assert.IsTrue (t.IsCompleted, "Task is not completed")
 
+    [<Test>]
+    member this.``AwaitTask ignores Async cancellation`` () =
+        let cts = new CancellationTokenSource()
+        let tcs = new TaskCompletionSource<unit>()
+        let innerTcs = new TaskCompletionSource<unit>()
+        let a = innerTcs.Task |> Async.AwaitTask
+
+        Async.StartWithContinuations(a, tcs.SetResult, tcs.SetException, ignore >> tcs.SetCanceled, cts.Token)
+
+        cts.CancelAfter(100)
+        try
+            let result = tcs.Task.Wait(300)
+            Assert.IsFalse (result)
+        with :? AggregateException -> Assert.Fail "Should not finish, yet"
+
+        innerTcs.SetResult ()
+
+        try
+            this.WaitASec tcs.Task
+        with :? AggregateException as a ->
+            match a.InnerException with
+            | :? TaskCanceledException -> ()
+            | _ -> reraise()
+        Assert.IsTrue (tcs.Task.IsCompleted, "Task is not completed")
+
     [<Test>]
     member this.StartTask () =
         let s = "Hello tasks!"