Emit AsyncIteratorStateMachine attribute on async-iterator methods (#31553)

src/Compilers/CSharp/Portable/Symbols/Source/SourceMemberMethodSymbol.cs

@@ -1636,13 +1636,19 @@ internal override void AddSynthesizedAttributes(PEModuleBuilder moduleBuilder, r
                 var arg = new TypedConstant(compilation.GetWellKnownType(WellKnownType.System_Type),
                     TypedConstantKind.Type, stateMachineType.GetUnboundGenericTypeOrSelf());
 
-                if (isAsync)
+                if (isAsync && isIterator)
+                {
+                    AddSynthesizedAttribute(ref attributes,
+                        compilation.TrySynthesizeAttribute(WellKnownMember.System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute__ctor,
+                            ImmutableArray.Create(arg)));
+                }
+                else if (isAsync)
                 {
                     AddSynthesizedAttribute(ref attributes,
                         compilation.TrySynthesizeAttribute(WellKnownMember.System_Runtime_CompilerServices_AsyncStateMachineAttribute__ctor,
                             ImmutableArray.Create(arg)));
                 }
-                if (isIterator)
+                else if (isIterator)
                 {
                     AddSynthesizedAttribute(ref attributes,
                         compilation.TrySynthesizeAttribute(WellKnownMember.System_Runtime_CompilerServices_IteratorStateMachineAttribute__ctor,

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncIteratorTests.cs

@@ -465,8 +465,35 @@ public static async System.Collections.Generic.IAsyncEnumerable<int> M()
             CompileAndVerify(comp, symbolValidator: module =>
             {
                 var method = module.GlobalNamespace.GetMember<MethodSymbol>("C.M");
-                AssertEx.SetEqual(new[] { "AsyncStateMachineAttribute", "IteratorStateMachineAttribute" },
+                AssertEx.SetEqual(new[] { "AsyncIteratorStateMachineAttribute" },
                     GetAttributeNames(method.GetAttributes()));
+
+                var attribute = method.GetAttributes().Single();
+                var argument = attribute.ConstructorArguments.Single();
+                Assert.Equal("System.Type", argument.Type.ToTestDisplayString());
+                Assert.Equal("C.<M>d__0", ((ITypeSymbol)argument.Value).ToTestDisplayString());
+            });
+        }
+
+        [ConditionalFact(typeof(WindowsDesktopOnly))]
+        public void AttributesSynthesized_Optional()
+        {
+            string source = @"
+public class C
+{
+    public static async System.Collections.Generic.IAsyncEnumerable<int> M()
+    {
+        await System.Threading.Tasks.Task.CompletedTask;
+        yield return 4;
+    }
+}";
+            var comp = CreateCompilationWithAsyncIterator(source, options: TestOptions.DebugDll);
+            comp.MakeTypeMissing(WellKnownType.System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute);
+            comp.VerifyDiagnostics();
+            CompileAndVerify(comp, symbolValidator: module =>
+            {
+                var method = module.GlobalNamespace.GetMember<MethodSymbol>("C.M");
+                Assert.Empty(GetAttributeNames(method.GetAttributes()));
             });
         }
 
@@ -1073,9 +1100,9 @@ async System.Collections.Generic.IAsyncEnumerator<int> M()
                 // (4,60): error CS8370: Feature 'async streams' is not available in C# 7.3. Please use language version 8.0 or greater.
                 //     async System.Collections.Generic.IAsyncEnumerator<int> M()
                 Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7_3, "M").WithArguments("async streams", "8.0").WithLocation(4, 60),
-                // (23,2): error CS8370: Feature 'nullable reference types' is not available in C# 7.3. Please use language version 8.0 or greater.
+                // (34,2): error CS8370: Feature 'nullable reference types' is not available in C# 7.3. Please use language version 8.0 or greater.
                 // #nullable disable
-                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7_3, "nullable").WithArguments("nullable reference types", "8.0").WithLocation(23, 2)
+                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7_3, "nullable").WithArguments("nullable reference types", "8.0").WithLocation(34, 2)
                 );
         }
 

src/Compilers/CSharp/Test/Symbol/Symbols/MissingSpecialMember.cs

@@ -566,6 +566,7 @@ public void AllWellKnownTypes()
                     case WellKnownType.System_Runtime_CompilerServices_IsUnmanagedAttribute:
                     case WellKnownType.System_Index:
                     case WellKnownType.System_Range:
+                    case WellKnownType.System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute:
                     case WellKnownType.System_IAsyncDisposable:
                     case WellKnownType.System_Collections_Generic_IAsyncEnumerable_T:
                     case WellKnownType.System_Collections_Generic_IAsyncEnumerator_T:
@@ -891,6 +892,7 @@ public void AllWellKnownTypeMembers()
                     case WellKnownMember.System_Range__Create:
                     case WellKnownMember.System_Range__FromStart:
                     case WellKnownMember.System_Range__ToEnd:
+                    case WellKnownMember.System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute__ctor:
                     case WellKnownMember.System_IAsyncDisposable__DisposeAsync:
                     case WellKnownMember.System_Collections_Generic_IAsyncEnumerable_T__GetAsyncEnumerator:
                     case WellKnownMember.System_Collections_Generic_IAsyncEnumerator_T__MoveNextAsync:

src/Compilers/Core/Portable/WellKnownMember.cs

@@ -456,6 +456,8 @@ internal enum WellKnownMember
         System_Range__FromStart,
         System_Range__All,
 
+        System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute__ctor,
+
         System_IAsyncDisposable__DisposeAsync,
         System_Collections_Generic_IAsyncEnumerable_T__GetAsyncEnumerator,
         System_Collections_Generic_IAsyncEnumerator_T__MoveNextAsync,
@@ -480,5 +482,7 @@ internal enum WellKnownMember
         System_Runtime_CompilerServices_AsyncIteratorMethodBuilder__MoveNext_T,
 
         Count
+
+        // Remember to update the AllWellKnownTypeMembers tests when making changes here
     }
 }

src/Compilers/Core/Portable/WellKnownMembers.cs

@@ -3137,6 +3137,14 @@ static WellKnownMembers()
                      0,                                                                                                                                         // Method Signature
                      (byte)SignatureTypeCode.TypeHandle, (byte)WellKnownType.ExtSentinel, (byte)(WellKnownType.System_Range - WellKnownType.ExtSentinel),
 
+                // System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute__ctor
+                (byte)MemberFlags.Constructor,                                                                              // Flags
+                (byte)WellKnownType.ExtSentinel, (byte)(WellKnownType.System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute - WellKnownType.ExtSentinel), // DeclaringTypeId
+                0,                                                                                                          // Arity
+                    1,                                                                                                      // Method Signature
+                    (byte)SignatureTypeCode.TypeHandle, (byte)SpecialType.System_Void, // Return Type
+                    (byte)SignatureTypeCode.TypeHandle, (byte)WellKnownType.System_Type,
+
                 // System_IAsyncDisposable__DisposeAsync
                 (byte)(MemberFlags.Method | MemberFlags.Virtual),                                                                                              // Flags
                 (byte)WellKnownType.ExtSentinel, (byte)(WellKnownType.System_IAsyncDisposable - WellKnownType.ExtSentinel),                                    // DeclaringTypeId
@@ -3707,6 +3715,8 @@ static WellKnownMembers()
                 "FromStart",                                // System_Range__FromStart
                 "All",                                      // System_Range__All
 
+                ".ctor",                                    // System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute__ctor
+
                 "DisposeAsync",                             // System_IAsyncDisposable__DisposeAsync
                 "GetAsyncEnumerator",                       // System_Collections_Generic_IAsyncEnumerable_T__GetAsyncEnumerator
                 "MoveNextAsync",                            // System_Collections_Generic_IAsyncEnumerator_T__MoveNextAsync
@@ -3757,6 +3767,7 @@ internal static bool IsSynthesizedAttributeOptional(WellKnownMember attributeMem
                 case WellKnownMember.System_STAThreadAttribute__ctor:
                 case WellKnownMember.System_Runtime_CompilerServices_AsyncStateMachineAttribute__ctor:
                 case WellKnownMember.System_Runtime_CompilerServices_IteratorStateMachineAttribute__ctor:
+                case WellKnownMember.System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute__ctor:
                     return true;
 
                 default:

src/Compilers/Core/Portable/WellKnownTypes.cs

@@ -280,6 +280,7 @@ internal enum WellKnownType
         System_Index,
         System_Range,
 
+        System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute,
         System_IAsyncDisposable,
         System_Collections_Generic_IAsyncEnumerable_T,
         System_Collections_Generic_IAsyncEnumerator_T,
@@ -292,6 +293,8 @@ internal enum WellKnownType
         System_Runtime_CompilerServices_AsyncIteratorMethodBuilder,
 
         NextAvailable,
+
+        // Remember to update the AllWellKnownTypes tests when making changes here
     }
 
     internal static class WellKnownTypes
@@ -565,6 +568,7 @@ internal static class WellKnownTypes
             "System.Index",
             "System.Range",
 
+            "System.Runtime.CompilerServices.AsyncIteratorStateMachineAttribute",
             "System.IAsyncDisposable",
             "System.Collections.Generic.IAsyncEnumerable`1",
             "System.Collections.Generic.IAsyncEnumerator`1",
@@ -627,11 +631,11 @@ private static void AssertEnumAndTableInSync()
                     typeIdName = typeIdName.Substring(0, separator);
                 }
 
-                Debug.Assert(name == typeIdName);
+                Debug.Assert(name == typeIdName, "Enum name and type name must match");
             }
 
             Debug.Assert((int)WellKnownType.ExtSentinel == 255);
-            Debug.Assert((int)WellKnownType.NextAvailable <= 512);
+            Debug.Assert((int)WellKnownType.NextAvailable <= 512, "Time for a new sentinel");
         }
 
         public static bool IsWellKnownType(this WellKnownType typeId)

src/Compilers/Test/Utilities/CSharp/CSharpTestBase.cs

@@ -132,6 +132,17 @@ public interface IAsyncDisposable
     }
 }
 
+namespace System.Runtime.CompilerServices
+{
+    [AttributeUsage(AttributeTargets.Method, Inherited = false, AllowMultiple = false)]
+    public sealed class AsyncIteratorStateMachineAttribute : StateMachineAttribute
+    {
+        public AsyncIteratorStateMachineAttribute(Type stateMachineType) : base(stateMachineType)
+        {
+        }
+    }
+}
+
 #nullable disable
 
 namespace System.Threading.Tasks.Sources

src/Compilers/VisualBasic/Test/Symbol/SymbolsTests/WellKnownTypeValidationTests.vb

@@ -507,6 +507,7 @@ End Namespace
                          WellKnownType.System_ReadOnlySpan_T,
                          WellKnownType.System_Index,
                          WellKnownType.System_Range,
+                         WellKnownType.System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute,
                          WellKnownType.System_IAsyncDisposable,
                          WellKnownType.System_Collections_Generic_IAsyncEnumerable_T,
                          WellKnownType.System_Collections_Generic_IAsyncEnumerator_T,
@@ -561,6 +562,7 @@ End Namespace
                          WellKnownType.System_ReadOnlySpan_T,
                          WellKnownType.System_Index,
                          WellKnownType.System_Range,
+                         WellKnownType.System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute,
                          WellKnownType.System_IAsyncDisposable,
                          WellKnownType.System_Collections_Generic_IAsyncEnumerable_T,
                          WellKnownType.System_Collections_Generic_IAsyncEnumerator_T,
@@ -623,6 +625,7 @@ End Namespace
                          WellKnownMember.System_ReadOnlySpan_T__ctor,
                          WellKnownMember.System_ReadOnlySpan_T__get_Item,
                          WellKnownMember.System_ReadOnlySpan_T__get_Length,
+                         WellKnownMember.System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute__ctor,
                          WellKnownMember.System_IAsyncDisposable__DisposeAsync,
                          WellKnownMember.System_Collections_Generic_IAsyncEnumerable_T__GetAsyncEnumerator,
                          WellKnownMember.System_Collections_Generic_IAsyncEnumerator_T__MoveNextAsync,
@@ -749,6 +752,7 @@ End Namespace
                          WellKnownMember.System_ReadOnlySpan_T__ctor,
                          WellKnownMember.System_ReadOnlySpan_T__get_Item,
                          WellKnownMember.System_ReadOnlySpan_T__get_Length,
+                         WellKnownMember.System_Runtime_CompilerServices_AsyncIteratorStateMachineAttribute__ctor,
                          WellKnownMember.System_IAsyncDisposable__DisposeAsync,
                          WellKnownMember.System_Collections_Generic_IAsyncEnumerable_T__GetAsyncEnumerator,
                          WellKnownMember.System_Collections_Generic_IAsyncEnumerator_T__MoveNextAsync,