Add Await operator for use in async setup expressions

src/Moq/ActionObserver.cs

@@ -8,9 +8,10 @@
 using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
-
+using System.Threading.Tasks;
 using Moq.Expressions.Visitors;
 using Moq.Internals;
+using Moq.Linq.Expressions;
 using Moq.Properties;
 
 using TypeNameFormatter;
@@ -28,10 +29,11 @@ internal sealed class ActionObserver : ExpressionReconstructor
 	{
 		public override Expression<Action<T>> ReconstructExpression<T>(Action<T> action, object[] ctorArgs = null)
 		{
+			using (var awaitOperatorObserver = AwaitOperatorObserver.Activate())
 			using (var matcherObserver = MatcherObserver.Activate())
 			{
 				// Create the root recording proxy:
-				var root = (T)CreateProxy(typeof(T), ctorArgs, matcherObserver, out var rootRecorder);
+				var root = (T)CreateProxy(typeof(T), ctorArgs, awaitOperatorObserver, matcherObserver, out var rootRecorder);
 
 				Exception error = null;
 				try
@@ -61,6 +63,12 @@ public override Expression<Action<T>> ReconstructExpression<T>(Action<T> action,
 					if (invocation != null)
 					{
 						body = Expression.Call(body, invocation.Method, GetArgumentExpressions(invocation, recorder.Matches.ToArray()));
+						if (recorder.Await)
+						{
+							var genArg = invocation.Method.ReturnType.GetGenericArguments()[0];
+							var awaitMethod = typeof(AwaitOperator).GetMethods("Await").First().MakeGenericMethod(genArg);
+							body = Expression.Call(awaitMethod, body);
+						}
 					}
 					else
 					{
@@ -213,32 +221,37 @@ bool CanDistribute(int msi, int asi)
 		}
 
 		// Creates a proxy (way more light-weight than a `Mock<T>`!) with an invocation `Recorder` attached to it.
-		private static IProxy CreateProxy(Type type, object[] ctorArgs, MatcherObserver matcherObserver, out Recorder recorder)
+		private static IProxy CreateProxy(Type type, object[] ctorArgs, AwaitOperatorObserver awaitOperatorObserver, MatcherObserver matcherObserver, out Recorder recorder)
 		{
-			recorder = new Recorder(matcherObserver);
+			recorder = new Recorder(awaitOperatorObserver, matcherObserver);
 			return (IProxy)ProxyFactory.Instance.CreateProxy(type, recorder, Type.EmptyTypes, ctorArgs ?? new object[0]);
 		}
 
 		// Records an invocation, mocks return values, and builds a chain to the return value's recorder.
 		// This record represents the basis for reconstructing an expression tree.
 		private sealed class Recorder : IInterceptor
 		{
+			private readonly AwaitOperatorObserver awaitOperatorObserver;
 			private readonly MatcherObserver matcherObserver;
 			private int creationTimestamp;
 			private Invocation invocation;
 			private int invocationTimestamp;
-			private IProxy returnValue;
+			private object returnValue;
 
-			public Recorder(MatcherObserver matcherObserver)
+			public Recorder(AwaitOperatorObserver awaitOperatorObserver, MatcherObserver matcherObserver)
 			{
+				Debug.Assert(awaitOperatorObserver != null);
 				Debug.Assert(matcherObserver != null);
 
+				this.awaitOperatorObserver = awaitOperatorObserver;
 				this.matcherObserver = matcherObserver;
 				this.creationTimestamp = this.matcherObserver.GetNextTimestamp();
 			}
 
 			public Invocation Invocation => this.invocation;
 
+			public bool Await => this.awaitOperatorObserver.HasAwaitOperatorBetween(this.creationTimestamp, this.invocationTimestamp);
+
 			public IEnumerable<Match> Matches
 			{
 				get
@@ -248,7 +261,7 @@ public IEnumerable<Match> Matches
 				}
 			}
 
-			public Recorder Next => this.returnValue?.Interceptor as Recorder;
+			public Recorder Next => (Unwrap.ResultIfCompletedTask(this.returnValue) as IProxy)?.Interceptor as Recorder;
 
 			public void Intercept(Invocation invocation)
 			{
@@ -277,9 +290,14 @@ public void Intercept(Invocation invocation)
 					{
 						this.returnValue = null;
 					}
+					else if (IsTaskType(returnType, out var resultType))
+					{
+						var result = CreateProxy(resultType, null, this.awaitOperatorObserver, this.matcherObserver, out _);
+						this.returnValue = Wrap.GetResultWrapper(returnType).Invoke(result);
+					}
 					else if (returnType.IsMockable())
 					{
-						this.returnValue = CreateProxy(returnType, null, this.matcherObserver, out _);
+						this.returnValue = CreateProxy(returnType, null, this.awaitOperatorObserver, this.matcherObserver, out _);
 					}
 					else
 					{
@@ -296,6 +314,22 @@ public void Intercept(Invocation invocation)
 					invocation.Return();
 				}
 			}
+
+			private static bool IsTaskType(Type type, out Type resultType)
+			{
+				if (type.IsGenericType)
+				{
+					var typeDef = type.GetGenericTypeDefinition();
+					if (typeDef == typeof(Task<>) || typeDef == typeof(ValueTask<>))
+					{
+						resultType = type.GetGenericArguments()[0];
+						return true;
+					}
+				}
+
+				resultType = null;
+				return false;
+			}
 		}
 	}
 }

src/Moq/AwaitOperatorObserver.cs

@@ -0,0 +1,94 @@
+// Copyright (c) 2007, Clarius Consulting, Manas Technology Solutions, InSTEDD.
+// All rights reserved. Licensed under the BSD 3-Clause License; see License.txt.
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+
+namespace Moq
+{
+	internal sealed class AwaitOperatorObserver : IDisposable
+	{
+		[ThreadStatic]
+		private static Stack<AwaitOperatorObserver> activations;
+
+		public static AwaitOperatorObserver Activate()
+		{
+			var activation = new AwaitOperatorObserver();
+
+			var activations = AwaitOperatorObserver.activations;
+			if (activations == null)
+			{
+				AwaitOperatorObserver.activations = activations = new Stack<AwaitOperatorObserver>();
+			}
+			activations.Push(activation);
+
+			return activation;
+		}
+
+		public static bool IsActive(out AwaitOperatorObserver observer)
+		{
+			var activations = AwaitOperatorObserver.activations;
+
+			if (activations != null && activations.Count > 0)
+			{
+				observer = activations.Peek();
+				return true;
+			}
+			else
+			{
+				observer = null;
+				return false;
+			}
+		}
+
+		private int timestamp;
+		private List<int> observations;
+
+		private AwaitOperatorObserver()
+		{
+		}
+
+		public void Dispose()
+		{
+			var activations = AwaitOperatorObserver.activations;
+			Debug.Assert(activations != null && activations.Count > 0);
+			activations.Pop();
+		}
+
+		/// <summary>
+		///   Returns the current timestamp. The next call will return a timestamp greater than this one,
+		///   allowing you to order invocations and matcher observations.
+		/// </summary>
+		public int GetNextTimestamp()
+		{
+			return ++this.timestamp;
+		}
+
+		/// <summary>
+		///   Adds the specified <see cref="Match"/> as an observation.
+		/// </summary>
+		public void OnAwaitOperator()
+		{
+			if (this.observations == null)
+			{
+				this.observations = new List<int>();
+			}
+
+			this.observations.Add(this.GetNextTimestamp());
+		}
+
+		public bool HasAwaitOperatorBetween(int fromTimestampInclusive, int toTimestampExclusive)
+		{
+			if (this.observations != null)
+			{
+				return this.observations.Any(o => fromTimestampInclusive <= o && o < toTimestampExclusive);
+			}
+			else
+			{
+				return false;
+			}
+		}
+	}
+}

src/Moq/ExpressionExtensions.cs

@@ -229,6 +229,11 @@ void Split(Expression e, out Expression r /* remainder */, out InvocationShape p
 										method,
 										arguments);
 						}
+						else if (methodCallExpression.Method.DeclaringType == typeof(Moq.Linq.Expressions.AwaitOperator))
+						{
+							Split(methodCallExpression.Arguments.Single(), out r, out p);
+							p.Await = true;
+						}
 						else
 						{
 							Debug.Assert(methodCallExpression.Method.IsExtensionMethod());

src/Moq/InvocationShape.cs

@@ -59,6 +59,8 @@ public InvocationShape(LambdaExpression expression, MethodInfo method, IReadOnly
 			this.exactGenericTypeArguments = exactGenericTypeArguments;
 		}
 
+		internal bool Await { get; set; }
+
 		public void Deconstruct(out LambdaExpression expression, out MethodInfo method, out IReadOnlyList<Expression> arguments)
 		{
 			expression = this.Expression;

src/Moq/Linq/Expressions/AwaitOperator.cs

@@ -0,0 +1,45 @@
+// Copyright (c) 2007, Clarius Consulting, Manas Technology Solutions, InSTEDD.
+// All rights reserved. Licensed under the BSD 3-Clause License; see License.txt.
+
+using System.Threading.Tasks;
+
+namespace Moq.Linq.Expressions
+{
+	/// <todo/>
+	public static class AwaitOperator
+	{
+		/// <todo/>
+		public static TResult Await<TResult>(Task<TResult> task)
+		{
+			return Impl(task.Result);
+		}
+
+		/// <todo/>
+		public static TResult Await<TResult>(ValueTask<TResult> task)
+		{
+			return Impl(task.Result);
+		}
+
+		/// <todo/>
+		public static TResult Result<TResult>(this Task<TResult> task)
+		{
+			return Impl(task.Result);
+		}
+
+		/// <todo/>
+		public static TResult Result<TResult>(this ValueTask<TResult> task)
+		{
+			return Impl(task.Result);
+		}
+
+		private static TResult Impl<TResult>(TResult result)
+		{
+			if (AwaitOperatorObserver.IsActive(out var o))
+			{
+				o.OnAwaitOperator();
+			}
+
+			return result;
+		}
+	}
+}

src/Moq/LookupOrFallbackDefaultValueProvider.cs

@@ -151,22 +151,14 @@ private object CreateTaskOf(Type type, Mock mock)
 		{
 			var resultType = type.GetGenericArguments()[0];
 			var result = this.GetDefaultValue(resultType, mock);
-
-			var tcsType = typeof(TaskCompletionSource<>).MakeGenericType(resultType);
-			var tcs = Activator.CreateInstance(tcsType);
-			tcsType.GetMethod("SetResult").Invoke(tcs, new[] { result });
-			return tcsType.GetProperty("Task").GetValue(tcs, null);
+			return Wrap.AsTask(type, result);
 		}
 
 		private object CreateValueTaskOf(Type type, Mock mock)
 		{
 			var resultType = type.GetGenericArguments()[0];
 			var result = this.GetDefaultValue(resultType, mock);
-
-			// `Activator.CreateInstance` could throw an `AmbiguousMatchException` in this use case,
-			// so we're explicitly selecting and calling the constructor we want to use:
-			var valueTaskCtor = type.GetConstructor(new[] { resultType });
-			return valueTaskCtor.Invoke(new object[] { result });
+			return Wrap.AsValueTask(type, result);
 		}
 
 		private object CreateValueTupleOf(Type type, Mock mock)