CA1822: Do not report on awaitable-awaiter

Author: Evangelink

src/NetAnalyzers/Core/Microsoft.CodeQuality.Analyzers/QualityGuidelines/MarkMembersAsStatic.cs

@@ -3,7 +3,6 @@
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Linq;
-using System.Threading;
 using Analyzer.Utilities;
 using Analyzer.Utilities.Extensions;
 using Analyzer.Utilities.PooledObjects;
@@ -230,6 +229,24 @@ private static bool ShouldAnalyze(
                 return false;
             }
 
+            // Awaitable-awaiter pattern members should not be marked as static.
+            // There is no need to check for INotifyCompletion or ICriticalNotifyCompletion members as they are already excluded.
+            if (wellKnownTypeProvider.TryGetOrCreateTypeByMetadataName(WellKnownTypeNames.SystemRuntimeCompilerServicesINotifyCompletion, out var inotifyCompletionType)
+                && wellKnownTypeProvider.TryGetOrCreateTypeByMetadataName(WellKnownTypeNames.SystemRuntimeCompilerServicesICriticalNotifyCompletion, out var icriticalNotifyCompletionType))
+            {
+                if (methodSymbol.IsGetAwaiterFromAwaitablePattern(inotifyCompletionType, icriticalNotifyCompletionType)
+                    || methodSymbol.IsGetResultFromAwaiterPattern(inotifyCompletionType, icriticalNotifyCompletionType))
+                {
+                    return false;
+                }
+
+                if (methodSymbol.AssociatedSymbol is IPropertySymbol property
+                    && property.IsIsCompletedFromAwaiterPattern(inotifyCompletionType, icriticalNotifyCompletionType))
+                {
+                    return false;
+                }
+            }
+
             var attributes = methodSymbol.GetAttributes();
             if (methodSymbol.AssociatedSymbol != null)
             {

src/NetAnalyzers/UnitTests/Microsoft.CodeQuality.Analyzers/QualityGuidelines/MarkMembersAsStaticTests.cs

@@ -1286,6 +1286,69 @@ public void M() {}
             }.RunAsync();
         }
 
+        [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 void GetResult()
+    {
+    }
+
+    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 void GetResult()
+    {
+    }
+
+    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 DiagnosticResult GetCSharpResultAt(int line, int column, string symbolName)
             => VerifyCS.Diagnostic()
                 .WithLocation(line, column)

src/Utilities/Compiler/Extensions/IMethodSymbolExtensions.cs

@@ -717,5 +717,48 @@ public static bool IsTopLevelStatementsEntryPointMethod([NotNullWhen(true)] this
                    "<Main>$" => true,
                    _ => false
                };
+
+        public static bool IsGetAwaiterFromAwaitablePattern([NotNullWhen(true)] this IMethodSymbol? method,
+            [NotNullWhen(true)] INamedTypeSymbol? inotifyCompletionType,
+            [NotNullWhen(true)] INamedTypeSymbol? icriticalNotifyCompletionType)
+        {
+            if (method is null
+                || !method.Name.Equals("GetAwaiter", StringComparison.Ordinal)
+                || method.Parameters.Length != 0)
+            {
+                return false;
+            }
+
+            var returnType = method.ReturnType?.OriginalDefinition;
+            if (returnType is null)
+            {
+                return false;
+            }
+
+            return returnType.DerivesFrom(inotifyCompletionType) ||
+                returnType.DerivesFrom(icriticalNotifyCompletionType);
+        }
+
+        public static bool IsGetResultFromAwaiterPattern(
+            [NotNullWhen(true)] this IMethodSymbol? method,
+            [NotNullWhen(true)] INamedTypeSymbol? inotifyCompletionType,
+            [NotNullWhen(true)] INamedTypeSymbol? icriticalNotifyCompletionType)
+        {
+            if (method is null
+                || !method.Name.Equals("GetResult", StringComparison.Ordinal)
+                || method.Parameters.Length != 0)
+            {
+                return false;
+            }
+
+            var containingType = method.ContainingType?.OriginalDefinition;
+            if (containingType is null)
+            {
+                return false;
+            }
+
+            return containingType.DerivesFrom(inotifyCompletionType) ||
+                containingType.DerivesFrom(icriticalNotifyCompletionType);
+        }
     }
 }

src/Utilities/Compiler/Extensions/IPropertySymbolExtensions.cs

@@ -1,5 +1,7 @@
 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using Microsoft.CodeAnalysis;
 
@@ -13,5 +15,22 @@ internal static class IPropertySymbolExtensions
         /// </summary>
         public static bool IsAutoProperty(this IPropertySymbol propertySymbol)
             => propertySymbol.ContainingType.GetMembers().OfType<IFieldSymbol>().Any(f => f.IsImplicitlyDeclared && propertySymbol.Equals(f.AssociatedSymbol));
+
+        public static bool IsIsCompletedFromAwaiterPattern(
+            [NotNullWhen(true)] this IPropertySymbol? property,
+            [NotNullWhen(true)] INamedTypeSymbol? inotifyCompletionType,
+            [NotNullWhen(true)] INamedTypeSymbol? icriticalNotifyCompletionType)
+        {
+            if (property is null
+                || !property.Name.Equals("IsCompleted", StringComparison.Ordinal)
+                || property.Type?.SpecialType != SpecialType.System_Boolean)
+            {
+                return false;
+            }
+
+            var containingType = property.ContainingType?.OriginalDefinition;
+            return containingType.DerivesFrom(inotifyCompletionType)
+                || containingType.DerivesFrom(icriticalNotifyCompletionType);
+        }
     }
 }

src/Utilities/Compiler/WellKnownTypeNames.cs

@@ -251,6 +251,8 @@ internal static class WellKnownTypeNames
         public const string SystemRuntimeCompilerServicesCallerMemberNameAttribute = "System.Runtime.CompilerServices.CallerMemberNameAttribute";
         public const string SystemRuntimeCompilerServicesCompilerGeneratedAttribute = "System.Runtime.CompilerServices.CompilerGeneratedAttribute";
         public const string SystemRuntimeCompilerServicesConfiguredValueTaskAwaitable1 = "System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable`1";
+        public const string SystemRuntimeCompilerServicesICriticalNotifyCompletion = "System.Runtime.CompilerServices.ICriticalNotifyCompletion";
+        public const string SystemRuntimeCompilerServicesINotifyCompletion = "System.Runtime.CompilerServices.INotifyCompletion";
         public const string SystemRuntimeCompilerServicesInternalsVisibleToAttribute = "System.Runtime.CompilerServices.InternalsVisibleToAttribute";
         public const string SystemRuntimeCompilerServicesRestrictedInternalsVisibleToAttribute = "System.Runtime.CompilerServices.RestrictedInternalsVisibleToAttribute";
         public const string SystemRuntimeCompilerServicesTypeForwardedToAttribute = "System.Runtime.CompilerServices.TypeForwardedToAttribute";