Enable tests for await using and DIM.

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -81,6 +81,7 @@
     <Compile Include="DisassemblerPrettyTestRunner.cs" />
     <Compile Include="TestCases\Correctness\StringConcat.cs" />
     <Compile Include="TestCases\ILPretty\ConstantBlobs.cs" />
+    <None Include="TestCases\Pretty\AsyncUsing.cs" />
     <Compile Include="TestCases\Pretty\OutVariables.cs" />
     <Compile Include="TestCases\Pretty\CustomTaskType.cs" />
     <None Include="TestCases\Ugly\NoExtensionMethods.Expected.cs" />

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -301,6 +301,12 @@ namespace ICSharpCode.Decompiler.Tests
 			Run(cscOptions: cscOptions);
 		}
 
+		[Test]
+		public void AsyncUsing([ValueSource(nameof(roslynOnlyOptions))] CompilerOptions cscOptions)
+		{
+			RunForLibrary(cscOptions: cscOptions);
+		}
+
 		[Test]
 		public void CustomTaskType([ValueSource(nameof(roslynOnlyOptions))] CompilerOptions cscOptions)
 		{

ICSharpCode.Decompiler.Tests/TestCases/Pretty/AsyncUsing.cs

@@ -0,0 +1,60 @@
+using System;
+using System.Runtime.InteropServices;
+using System.Threading.Tasks;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	internal class AsyncUsing
+	{
+		internal class AsyncDisposableClass : IAsyncDisposable
+		{
+			public ValueTask DisposeAsync()
+			{
+				throw new NotImplementedException();
+			}
+		}
+
+		[StructLayout(LayoutKind.Sequential, Size = 1)]
+		internal struct AsyncDisposableStruct : IAsyncDisposable
+		{
+			public ValueTask DisposeAsync()
+			{
+				throw new NotImplementedException();
+			}
+		}
+
+		public static async void TestAsyncUsing(IAsyncDisposable disposable)
+		{
+			await using (disposable) {
+				Console.WriteLine("Hello");
+			}
+		}
+
+		public static async void TestAsyncUsingClass()
+		{
+			await using (AsyncDisposableClass test = new AsyncDisposableClass()) {
+				Use(test);
+			}
+		}
+
+		public static async void TestAsyncUsingStruct()
+		{
+			await using (AsyncDisposableStruct asyncDisposableStruct = default(AsyncDisposableStruct)) {
+				Use(asyncDisposableStruct);
+			}
+		}
+
+		public static async void TestAsyncUsingNullableStruct()
+		{
+			await using (AsyncDisposableStruct? asyncDisposableStruct = new AsyncDisposableStruct?(default(AsyncDisposableStruct))) {
+				Use(asyncDisposableStruct);
+			}
+		}
+
+		private static void Use(IAsyncDisposable test)
+		{
+			throw new NotImplementedException();
+		}
+
+	}
+}

ICSharpCode.Decompiler.Tests/TestCases/Pretty/InterfaceTests.cs

@@ -16,9 +16,6 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
-// We can't test this because "error CS8701: Target runtime doesn't support default interface implementation."
-#undef CS80
-
 using System;
 
 namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty