Make 'await' resolve as in the C# 5.0 language specification.

This means that the awaiter type must implement INotifyCompletion and can optionally implement ICriticalNotifyCompletion.

ICSharpCode.NRefactory.CSharp/Resolver/AwaitResolveResult.cs

@@ -31,7 +31,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 	public class AwaitResolveResult : ResolveResult
 	{
 		/// <summary>
-		/// The method representing the GetAwaiter() call. Can be null if the GetAwaiter method was not found.
+		/// The method representing the GetAwaiter() call. Can be an <see cref="InvocationResolveResult"/> or a <see cref="DynamicInvocationResolveResult"/>.
 		/// </summary>
 		public readonly ResolveResult GetAwaiterInvocation;
 
@@ -47,6 +47,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 
 		/// <summary>
 		/// Method representing the OnCompleted method on the awaiter type. Can be null if the awaiter type or the method was not found, or when awaiting a dynamic expression.
+		/// This can also refer to an UnsafeOnCompleted method, if the awaiter type implements <c>System.Runtime.CompilerServices.ICriticalNotifyCompletion</c>.
 		/// </summary>
 		public readonly IMethod OnCompletedMethod;
 		

ICSharpCode.NRefactory.CSharp/Resolver/CSharpResolver.cs

@@ -383,7 +383,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 						return UnaryOperatorResolveResult(new PointerType(expression.Type), op, expression);
 					case UnaryOperatorType.Await: {
 						ResolveResult getAwaiterMethodGroup = ResolveMemberAccess(expression, "GetAwaiter", EmptyList<IType>.Instance, NameLookupMode.InvocationTarget);
-						ResolveResult getAwaiterInvocation = ResolveInvocation(getAwaiterMethodGroup, new ResolveResult[0]);
+						ResolveResult getAwaiterInvocation = ResolveInvocation(getAwaiterMethodGroup, new ResolveResult[0], argumentNames: null, allowOptionalParameters: false);
 
 						var lookup = CreateMemberLookup();
 						IMethod getResultMethod;
@@ -401,12 +401,21 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 
 						var isCompletedRR = lookup.Lookup(getAwaiterInvocation, "IsCompleted", EmptyList<IType>.Instance, false);
 						var isCompletedProperty = (isCompletedRR is MemberResolveResult ? ((MemberResolveResult)isCompletedRR).Member as IProperty : null);
+						if (isCompletedProperty != null && (!isCompletedProperty.ReturnType.IsKnownType(KnownTypeCode.Boolean) || !isCompletedProperty.CanGet))
+							isCompletedProperty = null;
+
+						var interfaceOnCompleted = compilation.FindType(KnownTypeCode.INotifyCompletion).GetMethods().FirstOrDefault(x => x.Name == "OnCompleted");
+						var interfaceUnsafeOnCompleted = compilation.FindType(KnownTypeCode.ICriticalNotifyCompletion).GetMethods().FirstOrDefault(x => x.Name == "UnsafeOnCompleted");
 
-						var onCompletedMethodGroup = lookup.Lookup(getAwaiterInvocation, "OnCompleted", EmptyList<IType>.Instance, true) as MethodGroupResolveResult;
 						IMethod onCompletedMethod = null;
-						if (onCompletedMethodGroup != null) {
-							var onCompletedOR = onCompletedMethodGroup.PerformOverloadResolution(compilation, new ResolveResult[] { new TypeResolveResult(compilation.FindType(new FullTypeName("System.Action")))  }, allowExtensionMethods: false, conversions: conversions);
-							onCompletedMethod = (onCompletedOR.FoundApplicableCandidate ? onCompletedOR.GetBestCandidateWithSubstitutedTypeArguments() as IMethod : null);
+						var candidates = getAwaiterInvocation.Type.GetMethods().Where(x => x.ImplementedInterfaceMembers.Contains(interfaceUnsafeOnCompleted)).ToList();
+						if (candidates.Count == 0) {
+							candidates = getAwaiterInvocation.Type.GetMethods().Where(x => x.ImplementedInterfaceMembers.Contains(interfaceOnCompleted)).ToList();
+							if (candidates.Count == 1)
+								onCompletedMethod = candidates[0];
+						}
+						else if (candidates.Count == 1) {
+							onCompletedMethod = candidates[0];
 						}
 
 						return new AwaitResolveResult(awaitResultType, getAwaiterInvocation, getAwaiterInvocation.Type, isCompletedProperty, onCompletedMethod, getResultMethod);
@@ -1927,19 +1936,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 			}
 		}
 
-		/// <summary>
-		/// Resolves an invocation.
-		/// </summary>
-		/// <param name="target">The target of the invocation. Usually a MethodGroupResolveResult.</param>
-		/// <param name="arguments">
-		/// Arguments passed to the method.
-		/// The resolver may mutate this array to wrap elements in <see cref="ConversionResolveResult"/>s!
-		/// </param>
-		/// <param name="argumentNames">
-		/// The argument names. Pass the null string for positional arguments.
-		/// </param>
-		/// <returns>InvocationResolveResult or UnknownMethodResolveResult</returns>
-		public ResolveResult ResolveInvocation(ResolveResult target, ResolveResult[] arguments, string[] argumentNames = null)
+		private ResolveResult ResolveInvocation(ResolveResult target, ResolveResult[] arguments, string[] argumentNames, bool allowOptionalParameters)
 		{
 			// C# 4.0 spec: §7.6.5
 			
@@ -1971,7 +1968,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 					}
 				}
 
-				OverloadResolution or = mgrr.PerformOverloadResolution(compilation, arguments, argumentNames, checkForOverflow: checkForOverflow, conversions: conversions);
+				OverloadResolution or = mgrr.PerformOverloadResolution(compilation, arguments, argumentNames, checkForOverflow: checkForOverflow, conversions: conversions, allowOptionalParameters: allowOptionalParameters);
 				if (or.BestCandidate != null) {
 					if (or.BestCandidate.IsStatic && !or.IsExtensionMethodInvocation && !(mgrr.TargetResult is TypeResolveResult))
 						return or.CreateResolveResult(new TypeResolveResult(mgrr.TargetType));
@@ -2005,6 +2002,23 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 			}
 			return ErrorResult;
 		}
+
+		/// <summary>
+		/// Resolves an invocation.
+		/// </summary>
+		/// <param name="target">The target of the invocation. Usually a MethodGroupResolveResult.</param>
+		/// <param name="arguments">
+		/// Arguments passed to the method.
+		/// The resolver may mutate this array to wrap elements in <see cref="ConversionResolveResult"/>s!
+		/// </param>
+		/// <param name="argumentNames">
+		/// The argument names. Pass the null string for positional arguments.
+		/// </param>
+		/// <returns>InvocationResolveResult or UnknownMethodResolveResult</returns>
+		public ResolveResult ResolveInvocation(ResolveResult target, ResolveResult[] arguments, string[] argumentNames = null)
+		{
+			return ResolveInvocation(target, arguments, argumentNames, allowOptionalParameters: true);
+		}
 		
 		List<IParameter> CreateParameters(ResolveResult[] arguments, string[] argumentNames)
 		{

ICSharpCode.NRefactory.CSharp/Resolver/FindReferences.cs

@@ -759,6 +759,7 @@ namespace ICSharpCode.NRefactory.CSharp.Resolver
 				case "GetAwaiter":
 				case "GetResult":
 				case "OnCompleted":
+				case "UnsafeOnCompleted":
 					specialNodeType = typeof(UnaryOperatorExpression);
 					break;
 				default:

ICSharpCode.NRefactory.Tests/CSharp/Resolver/FindReferencesTest.cs

@@ -213,8 +213,11 @@ class Calls {
 		#endregion
 
 		#region Await
+
+		#if NET_4_5
+
 		const string awaitTest = @"using System;
-class MyAwaiter {
+class MyAwaiter : System.Runtime.CompilerServices.INotifyCompletion {
 	public bool IsCompleted { get { return false; } }
 	public void OnCompleted(Action continuation) {}
 	public int GetResult() { return 0; }
@@ -268,6 +271,34 @@ public class C {
 			Assert.IsTrue(actual.Any(r => r.StartLocation.Line == 3 && r is PropertyDeclaration));
 			Assert.IsTrue(actual.Any(r => r.StartLocation.Line == 13 && r is UnaryOperatorExpression));
 		}
+
+		[Test]
+		public void UnsafeOnCompletedReferenceInAwaitExpressionIsFound() {
+			Init(@"using System;
+class MyAwaiter : System.Runtime.CompilerServices.ICriticalNotifyCompletion {
+	public bool IsCompleted { get { return false; } }
+	public void OnCompleted(Action continuation) {}
+	public void UnsafeOnCompleted(Action continuation) {}
+	public int GetResult() { return 0; }
+}
+class MyAwaitable {
+	public MyAwaiter GetAwaiter() { return null; }
+}
+public class C {
+	public async void M() {
+		MyAwaitable x = null;
+		int i = await x;
+	}
+}");
+			var test = compilation.MainAssembly.TopLevelTypeDefinitions.Single(t => t.Name == "MyAwaiter");
+			var method = test.Methods.Single(m => m.Name == "UnsafeOnCompleted");
+			var actual = FindReferences(method).ToList();
+			Assert.IsTrue(actual.Any(r => r.StartLocation.Line == 5 && r is MethodDeclaration));
+			Assert.IsTrue(actual.Any(r => r.StartLocation.Line == 14 && r is UnaryOperatorExpression));
+		}
+
+		#endif // NET_4_5
+
 		#endregion
 	}
 }

ICSharpCode.NRefactory.Tests/CSharp/Resolver/UnaryOperatorTests.cs

@@ -275,11 +275,12 @@ class Test {
 			Assert.AreEqual(unchecked( (ushort)~3 ), rr.ConstantValue);
 		}
 
+#if NET_4_5
 		[Test]
 		public void Await() {
 			string program = @"
 using System;
-class MyAwaiter {
+class MyAwaiter : System.Runtime.CompilerServices.INotifyCompletion {
 	public bool IsCompleted { get { return false; } }
 	public void OnCompleted(Action continuation) {}
 	public int GetResult() { return 0; }
@@ -322,7 +323,7 @@ public class C {
 			string program = @"
 using System;
 namespace N {
-	class MyAwaiter {
+	class MyAwaiter : System.Runtime.CompilerServices.INotifyCompletion {
 		public bool IsCompleted { get { return false; } }
 		public void OnCompleted(Action continuation) {}
 		public int GetResult() { return 0; }
@@ -363,11 +364,11 @@ namespace N {
 			Assert.AreEqual("N.MyAwaiter.GetResult", rr.GetResultMethod.FullName);
 		}
 
-		[Test, Ignore("TODO: MS C# (at least the RC version) refuses to use default values in GetAwaiter(). I do not know, however, if this is by design, and I could not find a simple, nice way to do the implementation")]
+		[Test]
 		public void GetAwaiterMethodWithDefaultArgumentCannotBeUsed() {
 			string program = @"
 using System;
-class MyAwaiter {
+class MyAwaiter : System.Runtime.CompilerServices.INotifyCompletion {
 	public bool IsCompleted { get { return false; } }
 	public void OnCompleted(Action continuation) {}
 	public int GetResult() { return 0; }
@@ -383,24 +384,16 @@ public class C {
 }";
 		
 			var rr = Resolve<AwaitResolveResult>(program);
-			Assert.IsFalse(rr.IsError);
-			Assert.AreEqual(SpecialType.UnknownType, rr.Type);
-			Assert.IsInstanceOf<CSharpInvocationResolveResult>(rr.GetAwaiterInvocation);
+			Assert.IsTrue(rr.IsError);
 			Assert.IsTrue(rr.GetAwaiterInvocation.IsError);
-
-			Assert.AreEqual(rr.AwaiterType, SpecialType.UnknownType);
-
-			Assert.IsNull(rr.IsCompletedProperty);
-			Assert.IsNull(rr.OnCompletedMethod);
-			Assert.IsNull(rr.GetResultMethod);
 		}
 
-		[Test, Ignore("TODO: MS C# (at least the RC version) refuses to use default values in GetAwaiter(). I do not know, however, if this is by design, and I could not find a simple, nice way to do the implementation")]
+		[Test, Ignore("TODO: MS C# refuses to use an extension method GetAwaiter() when there is an instance GetAwaiter() with only optional arguments. I do not know, however, if this is by design, and I could not find a simple, nice way to do the implementation")]
 		public void GetAwaiterMethodWithDefaultArgumentHidesExtensionMethodAndResultsInError() {
 			string program = @"
 using System;
 namespace N {
-	class MyAwaiter {
+	class MyAwaiter : System.Runtime.CompilerServices.INotifyCompletion {
 		public bool IsCompleted { get { return false; } }
 		public void OnCompleted(Action continuation) {}
 		public int GetResult() { return 0; }
@@ -420,7 +413,7 @@ namespace N {
 }";
 		
 			var rr = Resolve<AwaitResolveResult>(program);
-			Assert.IsFalse(rr.IsError);
+			Assert.IsTrue(rr.IsError);
 			Assert.AreEqual(SpecialType.UnknownType, rr.Type);
 			Assert.IsInstanceOf<CSharpInvocationResolveResult>(rr.GetAwaiterInvocation);
 			Assert.IsTrue(rr.GetAwaiterInvocation.IsError);
@@ -437,7 +430,7 @@ namespace N {
 			string program = @"
 using System;
 namespace N {
-	class MyAwaiter {
+	class MyAwaiter : System.Runtime.CompilerServices.INotifyCompletion {
 		public bool IsCompleted { get { return false; } }
 		public void OnCompleted(Action continuation) {}
 		public int GetResult() { return 0; }
@@ -479,12 +472,35 @@ namespace N {
 			Assert.AreEqual("N.MyAwaiter.GetResult", rr.GetResultMethod.FullName);
 		}
 
+		[Test]
+		public void GenericGetAwaiterResultsInError() {
+			string program = @"
+using System;
+class MyAwaiter : System.Runtime.CompilerServices.INotifyCompletion {
+	public bool IsCompleted { get { return false; } }
+	public void OnCompleted(Action continuation) {}
+	public int GetResult() { return 0; }
+}
+class MyAwaitable {
+	public MyAwaiter GetAwaiter<T>() { return null; }
+}
+public class C {
+	public async void M() {
+		MyAwaitable x = null;
+		int i = $await x$;
+	}
+}";
+		
+			var rr = Resolve<AwaitResolveResult>(program);
+			Assert.IsTrue(rr.IsError);
+		}
+
 		[Test]
 		public void AwaiterWithNoSuitableGetResult() {
 			string program = @"
 using System;
 namespace N {
-	class MyAwaiter {
+	class MyAwaiter : System.Runtime.CompilerServices.INotifyCompletion {
 		public bool IsCompleted { get { return false; } }
 		public void OnCompleted(Action continuation) {}
 		public int GetResult(int i) { return 0; }
@@ -525,15 +541,61 @@ namespace N {
 			Assert.IsNull(rr.GetResultMethod);
 		}
 
+		[Test]
+		public void AwaiterWithInaccessibleGetResult() {
+			string program = @"
+using System;
+namespace N {
+	class MyAwaiter : System.Runtime.CompilerServices.INotifyCompletion {
+		public bool IsCompleted { get { return false; } }
+		public void OnCompleted(Action continuation) {}
+		private int GetResult() { return 0; }
+	}
+	class MyAwaitable {
+		public static MyAwaiter GetAwaiter(int i) { return null; }
+	}
+	static class MyAwaitableExtensions {
+		public static MyAwaiter GetAwaiter(this MyAwaitable x) { return null; }
+	}
+	public class C {
+		public async void M() {
+			MyAwaitable x = null;
+			int i = $await x$;
+		}
+	}
+}";
+		
+			var rr = Resolve<AwaitResolveResult>(program);
+			Assert.IsTrue(rr.IsError);
+			Assert.AreEqual(SpecialType.UnknownType, rr.Type);
+			Assert.IsInstanceOf<CSharpInvocationResolveResult>(rr.GetAwaiterInvocation);
+			var getAwaiterInvocation = (CSharpInvocationResolveResult)rr.GetAwaiterInvocation;
+			Assert.IsFalse(rr.GetAwaiterInvocation.IsError);
+			Assert.AreEqual(1, getAwaiterInvocation.Arguments.Count);
+			Assert.AreEqual("N.MyAwaitableExtensions.GetAwaiter", getAwaiterInvocation.Member.FullName);
+			Assert.AreEqual(1, getAwaiterInvocation.Member.Parameters.Count);
+			Assert.IsTrue(getAwaiterInvocation.Arguments[0] is LocalResolveResult && ((LocalResolveResult)getAwaiterInvocation.Arguments[0]).Variable.Name == "x");
+
+			Assert.AreEqual("N.MyAwaiter", rr.AwaiterType.FullName);
+
+			Assert.IsNotNull(rr.IsCompletedProperty);
+			Assert.AreEqual("N.MyAwaiter.IsCompleted", rr.IsCompletedProperty.FullName);
+
+			Assert.IsNotNull(rr.OnCompletedMethod);
+			Assert.AreEqual("N.MyAwaiter.OnCompleted", rr.OnCompletedMethod.FullName);
+
+			Assert.IsNull(rr.GetResultMethod);
+		}
+
 		[Test]
 		public void AwaiterWithNoIsCompletedProperty() {
 			string program = @"
 using System;
 namespace N {
-	class MyAwaiter {
+	class MyAwaiter : System.Runtime.CompilerServices.INotifyCompletion {
 		public bool IsCompleted() { return false; }
 		public void OnCompleted(Action continuation) {}
-		public int GetResult(int i) { return 0; }
+		public int GetResult() { return 0; }
 	}
 	class MyAwaitable {
 		public static MyAwaiter GetAwaiter(int i) { return null; }
@@ -551,7 +613,7 @@ namespace N {
 		
 			var rr = Resolve<AwaitResolveResult>(program);
 			Assert.IsTrue(rr.IsError);
-			Assert.AreEqual(SpecialType.UnknownType, rr.Type);
+			Assert.IsTrue(rr.Type.IsKnownType(KnownTypeCode.Int32));
 			Assert.IsInstanceOf<CSharpInvocationResolveResult>(rr.GetAwaiterInvocation);
 			var getAwaiterInvocation = (CSharpInvocationResolveResult)rr.GetAwaiterInvocation;
 			Assert.IsFalse(rr.GetAwaiterInvocation.IsError);
@@ -567,16 +629,151 @@ namespace N {
 			Assert.IsNotNull(rr.OnCompletedMethod);
 			Assert.AreEqual("N.MyAwaiter.OnCompleted", rr.OnCompletedMethod.FullName);
 
-			Assert.IsNull(rr.GetResultMethod);
+			Assert.IsNotNull(rr.GetResultMethod);
+		}
+
+		[Test]
+		public void AwaiterWithIsCompletedPropertyThatIsNotBoolean() {
+			string program = @"
+using System;
+namespace N {
+	class MyAwaiter : System.Runtime.CompilerServices.INotifyCompletion {
+		public string IsCompleted { get { return false; } }
+		public void OnCompleted(Action continuation) {}
+		public int GetResult() { return 0; }
+	}
+	class MyAwaitable {
+		public static MyAwaiter GetAwaiter(int i) { return null; }
+	}
+	static class MyAwaitableExtensions {
+		public static MyAwaiter GetAwaiter(this MyAwaitable x) { return null; }
+	}
+	public class C {
+		public async void M() {
+			MyAwaitable x = null;
+			int i = $await x$;
+		}
+	}
+}";
+		
+			var rr = Resolve<AwaitResolveResult>(program);
+			Assert.IsTrue(rr.IsError);
+			Assert.IsTrue(rr.Type.IsKnownType(KnownTypeCode.Int32));
+			Assert.IsInstanceOf<CSharpInvocationResolveResult>(rr.GetAwaiterInvocation);
+			var getAwaiterInvocation = (CSharpInvocationResolveResult)rr.GetAwaiterInvocation;
+			Assert.IsFalse(rr.GetAwaiterInvocation.IsError);
+			Assert.AreEqual(1, getAwaiterInvocation.Arguments.Count);
+			Assert.AreEqual("N.MyAwaitableExtensions.GetAwaiter", getAwaiterInvocation.Member.FullName);
+			Assert.AreEqual(1, getAwaiterInvocation.Member.Parameters.Count);
+			Assert.IsTrue(getAwaiterInvocation.Arguments[0] is LocalResolveResult && ((LocalResolveResult)getAwaiterInvocation.Arguments[0]).Variable.Name == "x");
+
+			Assert.AreEqual("N.MyAwaiter", rr.AwaiterType.FullName);
+
+			Assert.IsNull(rr.IsCompletedProperty);
+
+			Assert.IsNotNull(rr.OnCompletedMethod);
+			Assert.AreEqual("N.MyAwaiter.OnCompleted", rr.OnCompletedMethod.FullName);
+
+			Assert.IsNotNull(rr.GetResultMethod);
 		}
 
 		[Test]
-		public void AwaiterWithNoOnCompletedMethodWithSuitableSignature() {
+		public void AwaiterWithIsCompletedPropertyThatIsNotReadable() {
+			string program = @"
+using System;
+namespace N {
+	class MyAwaiter : System.Runtime.CompilerServices.INotifyCompletion {
+		public bool IsCompleted { set {} }
+		public void OnCompleted(Action continuation) {}
+		public int GetResult() { return 0; }
+	}
+	class MyAwaitable {
+		public static MyAwaiter GetAwaiter(int i) { return null; }
+	}
+	static class MyAwaitableExtensions {
+		public static MyAwaiter GetAwaiter(this MyAwaitable x) { return null; }
+	}
+	public class C {
+		public async void M() {
+			MyAwaitable x = null;
+			int i = $await x$;
+		}
+	}
+}";
+		
+			var rr = Resolve<AwaitResolveResult>(program);
+			Assert.IsTrue(rr.IsError);
+			Assert.IsTrue(rr.Type.IsKnownType(KnownTypeCode.Int32));
+			Assert.IsInstanceOf<CSharpInvocationResolveResult>(rr.GetAwaiterInvocation);
+			var getAwaiterInvocation = (CSharpInvocationResolveResult)rr.GetAwaiterInvocation;
+			Assert.IsFalse(rr.GetAwaiterInvocation.IsError);
+			Assert.AreEqual(1, getAwaiterInvocation.Arguments.Count);
+			Assert.AreEqual("N.MyAwaitableExtensions.GetAwaiter", getAwaiterInvocation.Member.FullName);
+			Assert.AreEqual(1, getAwaiterInvocation.Member.Parameters.Count);
+			Assert.IsTrue(getAwaiterInvocation.Arguments[0] is LocalResolveResult && ((LocalResolveResult)getAwaiterInvocation.Arguments[0]).Variable.Name == "x");
+
+			Assert.AreEqual("N.MyAwaiter", rr.AwaiterType.FullName);
+
+			Assert.IsNull(rr.IsCompletedProperty);
+
+			Assert.IsNotNull(rr.OnCompletedMethod);
+			Assert.AreEqual("N.MyAwaiter.OnCompleted", rr.OnCompletedMethod.FullName);
+
+			Assert.IsNotNull(rr.GetResultMethod);
+		}
+
+		[Test]
+		public void AwaiterWithIsCompletedPropertyThatIsNotAccessible() {
+			string program = @"
+using System;
+namespace N {
+	class MyAwaiter : System.Runtime.CompilerServices.INotifyCompletion {
+		private bool IsCompleted { get; set; }
+		public void OnCompleted(Action continuation) {}
+		public int GetResult() { return 0; }
+	}
+	class MyAwaitable {
+		public static MyAwaiter GetAwaiter(int i) { return null; }
+	}
+	static class MyAwaitableExtensions {
+		public static MyAwaiter GetAwaiter(this MyAwaitable x) { return null; }
+	}
+	public class C {
+		public async void M() {
+			MyAwaitable x = null;
+			int i = $await x$;
+		}
+	}
+}";
+		
+			var rr = Resolve<AwaitResolveResult>(program);
+			Assert.IsTrue(rr.IsError);
+			Assert.IsTrue(rr.Type.IsKnownType(KnownTypeCode.Int32));
+			Assert.IsInstanceOf<CSharpInvocationResolveResult>(rr.GetAwaiterInvocation);
+			var getAwaiterInvocation = (CSharpInvocationResolveResult)rr.GetAwaiterInvocation;
+			Assert.IsFalse(rr.GetAwaiterInvocation.IsError);
+			Assert.AreEqual(1, getAwaiterInvocation.Arguments.Count);
+			Assert.AreEqual("N.MyAwaitableExtensions.GetAwaiter", getAwaiterInvocation.Member.FullName);
+			Assert.AreEqual(1, getAwaiterInvocation.Member.Parameters.Count);
+			Assert.IsTrue(getAwaiterInvocation.Arguments[0] is LocalResolveResult && ((LocalResolveResult)getAwaiterInvocation.Arguments[0]).Variable.Name == "x");
+
+			Assert.AreEqual("N.MyAwaiter", rr.AwaiterType.FullName);
+
+			Assert.IsNull(rr.IsCompletedProperty);
+
+			Assert.IsNotNull(rr.OnCompletedMethod);
+			Assert.AreEqual("N.MyAwaiter.OnCompleted", rr.OnCompletedMethod.FullName);
+
+			Assert.IsNotNull(rr.GetResultMethod);
+		}
+
+		[Test]
+		public void AwaiterThatDoesNotImplementINotifyCompletion() {
 			string program = @"
 using System;
 class MyAwaiter {
 	public bool IsCompleted { get { return false; } }
-	public void OnCompleted(Func<int> continuation) {}
+	public void OnCompleted(Action continuation) {}
 	public int GetResult() { return 0; }
 }
 class MyAwaitable {
@@ -611,6 +808,49 @@ public class C {
 			Assert.AreEqual("MyAwaiter.GetResult", rr.GetResultMethod.FullName);
 		}
 
+		[Test]
+		public void AwaiterThatImplementsICriticalNotifyCompletion() {
+			string program = @"
+using System;
+class MyAwaiter : System.Runtime.CompilerServices.ICriticalNotifyCompletion {
+	public bool IsCompleted { get { return false; } }
+	public void OnCompleted(Action continuation) {}
+	public void UnsafeOnCompleted(Action continuation) {}
+	public int GetResult() { return 0; }
+}
+class MyAwaitable {
+	public MyAwaiter GetAwaiter() { return null; }
+	public MyAwaiter GetAwaiter(int i) { return null; }
+}
+public class C {
+	public async void M() {
+		MyAwaitable x = null;
+		int i = $await x$;
+	}
+}";
+		
+			var rr = Resolve<AwaitResolveResult>(program);
+			Assert.IsFalse(rr.IsError);
+			Assert.IsTrue(rr.Type.IsKnownType(KnownTypeCode.Int32));
+			Assert.IsInstanceOf<CSharpInvocationResolveResult>(rr.GetAwaiterInvocation);
+			var getAwaiterInvocation = (CSharpInvocationResolveResult)rr.GetAwaiterInvocation;
+			Assert.IsFalse(rr.GetAwaiterInvocation.IsError);
+			Assert.AreEqual(0, getAwaiterInvocation.Arguments.Count);
+			Assert.AreEqual("MyAwaitable.GetAwaiter", getAwaiterInvocation.Member.FullName);
+			Assert.AreEqual(0, getAwaiterInvocation.Member.Parameters.Count);
+
+			Assert.AreEqual("MyAwaiter", rr.AwaiterType.FullName);
+
+			Assert.IsNotNull(rr.IsCompletedProperty);
+			Assert.AreEqual("MyAwaiter.IsCompleted", rr.IsCompletedProperty.FullName);
+
+			Assert.IsNotNull(rr.OnCompletedMethod);
+			Assert.AreEqual("MyAwaiter.UnsafeOnCompleted", rr.OnCompletedMethod.FullName);
+
+			Assert.IsNotNull(rr.GetResultMethod);
+			Assert.AreEqual("MyAwaiter.GetResult", rr.GetResultMethod.FullName);
+		}
+
 		[Test]
 		public void AwaitDynamic() {
 			string program = @"
@@ -640,5 +880,6 @@ public class C {
 			Assert.IsNull(rr.OnCompletedMethod);
 			Assert.IsNull(rr.GetResultMethod);
 		}
+#endif // NET_4_5
 	}
 }

ICSharpCode.NRefactory/TypeSystem/KnownTypeReference.cs

@@ -118,7 +118,11 @@ namespace ICSharpCode.NRefactory.TypeSystem
 		/// <summary><c>System.Nullable{T}</c></summary>
 		NullableOfT,
 		/// <summary><c>System.IDisposable</c></summary>
-		IDisposable
+		IDisposable,
+		/// <summary><c>System.Runtime.CompilerServices.INotifyCompletion</c></summary>
+		INotifyCompletion,
+		/// <summary><c>System.Runtime.CompilerServices.ICriticalNotifyCompletion</c></summary>
+		ICriticalNotifyCompletion,
 	}
 	
 	/// <summary>
@@ -127,7 +131,7 @@ namespace ICSharpCode.NRefactory.TypeSystem
 	[Serializable]
 	public sealed class KnownTypeReference : ITypeReference
 	{
-		internal const int KnownTypeCodeCount = (int)KnownTypeCode.IDisposable + 1;
+		internal const int KnownTypeCodeCount = (int)KnownTypeCode.ICriticalNotifyCompletion + 1;
 		
 		static readonly KnownTypeReference[] knownTypeReferences = new KnownTypeReference[KnownTypeCodeCount] {
 			null, // None
@@ -174,6 +178,8 @@ namespace ICSharpCode.NRefactory.TypeSystem
 			new KnownTypeReference(KnownTypeCode.TaskOfT,     "System.Threading.Tasks", "Task", 1, baseType: KnownTypeCode.Task),
 			new KnownTypeReference(KnownTypeCode.NullableOfT, "System", "Nullable", 1, baseType: KnownTypeCode.ValueType),
 			new KnownTypeReference(KnownTypeCode.IDisposable, "System", "IDisposable"),
+			new KnownTypeReference(KnownTypeCode.INotifyCompletion, "System.Runtime.CompilerServices", "INotifyCompletion"),
+			new KnownTypeReference(KnownTypeCode.ICriticalNotifyCompletion, "System.Runtime.CompilerServices", "ICriticalNotifyCompletion"),
 		};
 		
 		/// <summary>
@@ -389,7 +395,17 @@ namespace ICSharpCode.NRefactory.TypeSystem
 		/// Gets a type reference pointing to the <c>System.IDisposable</c> type.
 		/// </summary>
 		public static readonly KnownTypeReference IDisposable = Get(KnownTypeCode.IDisposable);
-		
+
+		/// <summary>
+		/// Gets a type reference pointing to the <c>System.Runtime.CompilerServices.INotifyCompletion</c> type.
+		/// </summary>
+		public static readonly KnownTypeReference INotifyCompletion = Get(KnownTypeCode.INotifyCompletion);
+
+		/// <summary>
+		/// Gets a type reference pointing to the <c>System.Runtime.CompilerServices.ICriticalNotifyCompletion</c> type.
+		/// </summary>
+		public static readonly KnownTypeReference ICriticalNotifyCompletion = Get(KnownTypeCode.ICriticalNotifyCompletion);
+
 		readonly KnownTypeCode knownTypeCode;
 		readonly string namespaceName;
 		readonly string name;