CA1024: Do not report on awaitable-awaiter

Author: Evangelink

src/NetAnalyzers/Core/Microsoft.CodeQuality.Analyzers/ApiDesignGuidelines/UsePropertiesWhereAppropriate.cs

@@ -56,6 +56,11 @@ public override void Initialize(AnalysisContext analysisContext)
 
                 var taskTypes = taskTypesBuilder.ToImmutable();
 
+                var inotifyCompletionType = context.Compilation.GetOrCreateTypeByMetadataName(
+                    WellKnownTypeNames.SystemRuntimeCompilerServicesINotifyCompletion);
+                var icriticalNotifyCompletionType = context.Compilation.GetOrCreateTypeByMetadataName(
+                    WellKnownTypeNames.SystemRuntimeCompilerServicesICriticalNotifyCompletion);
+
                 context.RegisterOperationBlockStartAction(context =>
                 {
                     if (context.OwningSymbol is not IMethodSymbol methodSymbol ||
@@ -73,14 +78,17 @@ public override void Initialize(AnalysisContext analysisContext)
                     // Ensure that the method is non-generic, non-virtual/override, has no overloads and doesn't have special names: 'GetHashCode' or 'GetEnumerator'.
                     // Also avoid generating this diagnostic if the method body has any invocation expressions.
                     // Also avoid implicit interface implementation (explicit are handled through the member accessibility)
+                    // Also avoid GetAwaiter and GetResult from awaitable-awaiter patterns.
                     if (methodSymbol.IsGenericMethod ||
                         methodSymbol.IsVirtual ||
                         methodSymbol.IsOverride ||
                         methodSymbol.Name == GetHashCodeName ||
                         methodSymbol.Name == GetEnumeratorName ||
                         methodSymbol.ContainingType.GetMembers(methodSymbol.Name).Length > 1 ||
                         taskTypes.Contains(methodSymbol.ReturnType.OriginalDefinition) ||
-                        methodSymbol.IsImplementationOfAnyImplicitInterfaceMember())
+                        methodSymbol.IsImplementationOfAnyImplicitInterfaceMember() ||
+                        methodSymbol.IsGetAwaiterFromAwaitablePattern(inotifyCompletionType, icriticalNotifyCompletionType) ||
+                        methodSymbol.IsGetResultFromAwaiterPattern(inotifyCompletionType, icriticalNotifyCompletionType))
                     {
                         return;
                     }

src/NetAnalyzers/UnitTests/Microsoft.CodeQuality.Analyzers/ApiDesignGuidelines/UsePropertiesWhereAppropriateTests.cs

@@ -478,6 +478,65 @@ End Class
 ");
         }
 
+        [Fact, WorkItem(4623, "https://github.com/dotnet/roslyn-analyzers/issues/4623")]
+        public async Task AwaiterPattern_INotifyCompletion_NoDiagnostic()
+        {
+            await VerifyCS.VerifyAnalyzerAsync(@"
+using System;
+using System.Runtime.CompilerServices;
+
+public class DummyAwaiter : INotifyCompletion
+{
+    public object GetResult() => null;
+
+    public bool IsCompleted => false;
+
+    public void OnCompleted(Action continuation) => throw null;
+}");
+        }
+
+        [Fact, WorkItem(4623, "https://github.com/dotnet/roslyn-analyzers/issues/4623")]
+        public async Task AwaiterPattern_ICriticalNotifyCompletion_NoDiagnostic()
+        {
+            await VerifyCS.VerifyAnalyzerAsync(@"
+using System;
+using System.Runtime.CompilerServices;
+
+public class DummyAwaiter : ICriticalNotifyCompletion
+{
+    public object GetResult() => null;
+
+    public bool IsCompleted => false;
+
+    public void OnCompleted(Action continuation) => throw null;
+    public void UnsafeOnCompleted(Action continuation) => throw null;
+}");
+        }
+
+        [Fact, WorkItem(4623, "https://github.com/dotnet/roslyn-analyzers/issues/4623")]
+        public async Task AwaitablePattern_NoDiagnostic()
+        {
+            await VerifyCS.VerifyAnalyzerAsync(@"
+using System;
+using System.Runtime.CompilerServices;
+
+public class DummyAwaitable
+{
+    public DummyAwaiter GetAwaiter() => new DummyAwaiter();
+}
+
+public class DummyAwaiter : INotifyCompletion
+{
+    public void GetResult()
+    {
+    }
+
+    public bool IsCompleted => false;
+
+    public void OnCompleted(Action continuation) => throw null;
+}");
+        }
+
         private static DiagnosticResult GetCA1024CSharpResultAt(int line, int column, string methodName)
             => VerifyCS.Diagnostic()
                 .WithLocation(line, column)