Test IDISP005 when IAsyncDisposable

#199

Author: JohanLarsson

IDisposableAnalyzers.NetCoreTests/IDISP005ReturnTypeShouldBeIDisposableTests/Valid.cs

@@ -0,0 +1,31 @@
+namespace IDisposableAnalyzers.NetCoreTests.IDISP005ReturnTypeShouldBeIDisposableTests
+{
+    using Gu.Roslyn.Asserts;
+    using Microsoft.CodeAnalysis;
+    using Microsoft.CodeAnalysis.Diagnostics;
+    using NUnit.Framework;
+
+    public static class Valid
+    {
+        private static readonly DiagnosticAnalyzer Analyzer = new ReturnValueAnalyzer();
+        private static readonly DiagnosticDescriptor Descriptor = Descriptors.IDISP005ReturnTypeShouldBeIDisposable;
+
+        [Test]
+        public static void LocalDisposeAsync()
+        {
+            var code = @"
+namespace N
+{
+    using System;
+    using System.IO;
+
+    public class C
+    {
+        public IAsyncDisposable M() => File.OpenRead(string.Empty);
+    }
+}";
+
+            RoslynAssert.Valid(Analyzer, code);
+        }
+    }
+}

IDisposableAnalyzers/Analyzers/ReturnValueAnalyzer.cs

@@ -189,22 +189,25 @@ private static bool IsDisposableReturnTypeOrIgnored(ITypeSymbol? type, Compilati
                 return true;
             }
 
+            if (type == KnownSymbol.IAsyncDisposable)
+            {
+                return true;
+            }
+
             if (type == KnownSymbol.IEnumerator)
             {
                 return true;
             }
 
             if (type == KnownSymbol.Task)
             {
-                var namedType = type as INamedTypeSymbol;
-                return namedType?.IsGenericType == true &&
+                return type is INamedTypeSymbol { IsGenericType: true } namedType &&
                        Disposable.IsAssignableFrom(namedType.TypeArguments[0], compilation);
             }
 
             if (type == KnownSymbol.Func)
             {
-                var namedType = type as INamedTypeSymbol;
-                return namedType?.IsGenericType == true &&
+                return type is INamedTypeSymbol { IsGenericType: true } namedType &&
                        Disposable.IsAssignableFrom(namedType.TypeArguments[namedType.TypeArguments.Length - 1], compilation);
             }