Fix type mismatch during callback validation for task .Result setups

CHANGELOG.md

@@ -14,6 +14,8 @@ The format is loosely based on [Keep a Changelog](http://keepachangelog.com/en/1
 
 * `AmbiguousMatchException` raised when interface has property indexer besides property in VB. (@mujdatdinc, #1129)
 * Interface default methods are ignored (@hahn-kev, #972)
+* Callback validation too strict when setting up a task's `.Result` property (@stakx, #1132)
+
 
 ## 4.16.0 (2021-01-16)
 

src/Moq/MethodCall.cs

@@ -13,6 +13,8 @@
 using Moq.Behaviors;
 using Moq.Properties;
 
+using TypeNameFormatter;
+
 namespace Moq
 {
 	internal sealed partial class MethodCall : SetupWithOutParameterSupport
@@ -310,7 +312,8 @@ void ValidateCallback(Delegate callback)
 					throw new ArgumentException(Resources.InvalidReturnsCallbackNotADelegateWithReturnType);
 				}
 
-				var expectedReturnType = this.Method.ReturnType;
+				var expectedReturnType = this.Expectation.HasResultExpression(out var awaitable) ? awaitable.ResultType
+				                                                                                 : this.Method.ReturnType;
 
 				if (!expectedReturnType.IsAssignableFrom(actualReturnType))
 				{
@@ -321,8 +324,8 @@ void ValidateCallback(Delegate callback)
 							string.Format(
 								CultureInfo.CurrentCulture,
 								Resources.InvalidCallbackReturnTypeMismatch,
-								expectedReturnType,
-								actualReturnType));
+								expectedReturnType.GetFormattedName(),
+								actualReturnType.GetFormattedName()));
 					}
 				}
 			}

src/Moq/Properties/Resources.resx

@@ -285,7 +285,7 @@ Remember that there's no generics covariance in the CLR, so your object must be
     <value>Type {0} does not have matching protected member: {1}</value>
   </data>
   <data name="InvalidCallbackReturnTypeMismatch" xml:space="preserve">
-    <value>Invalid callback. Setup on method with return type ({0}) cannot invoke callback with return type ({1}).</value>
+    <value>Invalid callback. Setup on method with return type '{0}' cannot invoke callback with return type '{1}'.</value>
   </data>
   <data name="InvalidCallbackParameterCountMismatch" xml:space="preserve">
     <value>Invalid callback. Setup on method with {0} parameter(s) cannot invoke callback with different number of parameters ({1}).</value>

tests/Moq.Tests/SetupTaskResultFixture.cs

@@ -101,6 +101,15 @@ public async Task Setup__completed_Task__Returns()
 			Assert.Same(Friend, friend);
 		}
 
+		[Fact]
+		public async Task Setup__completed_Task__Returns_callback()
+		{
+			var person = new Mock<IPerson>();
+			person.Setup(p => p.GetFriendTaskAsync().Result).Returns(() => Friend);
+			var friend = await person.Object.GetFriendTaskAsync();
+			Assert.Same(Friend, friend);
+		}
+
 		[Fact]
 		public async Task Setup__completed_Task__Throws()
 		{
@@ -119,6 +128,15 @@ public async Task Setup__completed_ValueTask__Returns()
 			Assert.Same(Friend, friend);
 		}
 
+		[Fact]
+		public async Task Setup__completed_ValueTask__Returns_callback()
+		{
+			var person = new Mock<IPerson>();
+			person.Setup(p => p.GetFriendValueTaskAsync().Result).Returns(()=> Friend);
+			var friend = await person.Object.GetFriendValueTaskAsync();
+			Assert.Same(Friend, friend);
+		}
+
 		[Fact]
 		public async Task Setup__completed_ValueTask__Throws()
 		{