test async enumerable

Directory.Build.props

@@ -2,4 +2,7 @@
   <PropertyGroup>
     <LangVersion>latest</LangVersion>
   </PropertyGroup>
+  <PropertyGroup Condition="'$(TargetFramework)' != 'netstandard2.0' and !$(TargetFramework.StartsWith('netcoreapp2')) and !$(TargetFramework.StartsWith('net4'))">
+    <DefineConstants>$(DefineConstants);HAS_ASYNC_ENUMERATOR</DefineConstants>
+  </PropertyGroup>
 </Project>

src/Ben.Demystifier/EnhancedStackTrace.Frames.cs

@@ -845,7 +845,7 @@ namespace System.Diagnostics
                     {
                         foundAttribute = true;
                         foundIteratorAttribute |= asma is IteratorStateMachineAttribute
-#if NETSTANDARD2_1
+#if HAS_ASYNC_ENUMERATOR
                             || asma is AsyncIteratorStateMachineAttribute
 #endif
                             ;

test/Ben.Demystifier.Test/AsyncEnumerableTests.cs

@@ -0,0 +1,68 @@
+#if HAS_ASYNC_ENUMERATOR
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Ben.Demystifier.Test
+{
+    public class AsyncEnumerableTests
+    {
+        [Fact]
+        public async Task DemystifiesAsyncEnumerable()
+        {
+            Exception demystifiedException = null;
+
+            try
+            {
+                await foreach (var val in Start(CancellationToken.None))
+                {
+                    _ = val;
+                }
+            }
+            catch (Exception ex)
+            {
+                demystifiedException = ex.Demystify();
+            }
+
+            // Assert
+            var stackTrace = demystifiedException.ToString();
+            stackTrace = LineEndingsHelper.RemoveLineEndings(stackTrace);
+            var trace = string.Join("", stackTrace.Split(new[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries)
+                .Skip(1)
+                .ToArray());
+            var expected = string.Join("", new[] {
+                "   at async IAsyncEnumerable<int> Ben.Demystifier.Test.AsyncEnumerableTests.Throw(CancellationToken cancellationToken)+MoveNext()",
+                "   at async IAsyncEnumerable<int> Ben.Demystifier.Test.AsyncEnumerableTests.Throw(CancellationToken cancellationToken)+System.Threading.Tasks.Sources.IValueTaskSource<System.Boolean>.GetResult(short token)",
+                "   at async IAsyncEnumerable<long> Ben.Demystifier.Test.AsyncEnumerableTests.Start(CancellationToken cancellationToken)+MoveNext()",
+                "   at async IAsyncEnumerable<long> Ben.Demystifier.Test.AsyncEnumerableTests.Start(CancellationToken cancellationToken)+MoveNext()",
+                "   at async IAsyncEnumerable<long> Ben.Demystifier.Test.AsyncEnumerableTests.Start(CancellationToken cancellationToken)+System.Threading.Tasks.Sources.IValueTaskSource<System.Boolean>.GetResult(short token)",
+                "   at async Task Ben.Demystifier.Test.AsyncEnumerableTests.DemystifiesAsyncEnumerable()",
+                "   at async Task Ben.Demystifier.Test.AsyncEnumerableTests.DemystifiesAsyncEnumerable()"
+            });
+            Assert.Equal(expected, trace);
+        }
+
+        async IAsyncEnumerable<long> Start([EnumeratorCancellation] CancellationToken cancellationToken)
+        {
+            await Task.Delay(1, cancellationToken).ConfigureAwait(false);
+            yield return 1;
+            await foreach (var @throw in Throw(cancellationToken))
+            {
+                yield return @throw;
+            }
+        }
+
+        async IAsyncEnumerable<int> Throw([EnumeratorCancellation] CancellationToken cancellationToken)
+        {
+            yield return 2;
+            await Task.Delay(1, cancellationToken).ConfigureAwait(false);
+            throw new InvalidOperationException();
+        }
+    }
+}
+#endif