Add ability in IAwaitableFactory to create result expression

Author: stakx

src/Moq/Async/AwaitExpression.cs

@@ -0,0 +1,40 @@
+// Copyright (c) 2007, Clarius Consulting, Manas Technology Solutions, InSTEDD, and Contributors.
+// All rights reserved. Licensed under the BSD 3-Clause License; see License.txt.
+
+using System;
+using System.Diagnostics;
+using System.Linq.Expressions;
+
+namespace Moq.Async
+{
+	internal sealed class AwaitExpression : Expression
+	{
+		private readonly IAwaitableFactory awaitableFactory;
+		private readonly Expression operand;
+
+		public AwaitExpression(Expression operand, IAwaitableFactory awaitableFactory)
+		{
+			Debug.Assert(awaitableFactory != null);
+			Debug.Assert(operand != null);
+
+			this.awaitableFactory = awaitableFactory;
+			this.operand = operand;
+		}
+
+		public override bool CanReduce => false;
+
+		public override ExpressionType NodeType => ExpressionType.Extension;
+
+		public Expression Operand => this.operand;
+
+		public override Type Type => this.awaitableFactory.ResultType;
+
+		public override string ToString()
+		{
+			return this.awaitableFactory.ResultType == typeof(void) ? $"await {this.operand}"
+			                                                        : $"(await {this.operand})";
+		}
+
+		protected override Expression VisitChildren(ExpressionVisitor visitor) => this;
+	}
+}

src/Moq/Async/AwaitableFactory`1.cs

@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using System.Linq.Expressions;
 
 namespace Moq.Async
 {
@@ -44,6 +45,11 @@ object IAwaitableFactory.CreateFaulted(IEnumerable<Exception> exceptions)
 			return this.CreateFaulted(exceptions);
 		}
 
+		Expression IAwaitableFactory.CreateResultExpression(Expression awaitableExpression)
+		{
+			return new AwaitExpression(awaitableExpression, this);
+		}
+
 		bool IAwaitableFactory.TryGetResult(object awaitable, out object result)
 		{
 			Debug.Assert(awaitable is TAwaitable);

src/Moq/Async/AwaitableFactory`2.cs

@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using System.Linq.Expressions;
 
 namespace Moq.Async
 {
@@ -46,6 +47,8 @@ object IAwaitableFactory.CreateFaulted(IEnumerable<Exception> exceptions)
 
 		public abstract bool TryGetResult(TAwaitable awaitable, out TResult result);
 
+		public abstract Expression CreateResultExpression(Expression awaitableExpression);
+
 		bool IAwaitableFactory.TryGetResult(object awaitable, out object result)
 		{
 			Debug.Assert(awaitable is TAwaitable);

src/Moq/Async/IAwaitableFactory.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq.Expressions;
 
 namespace Moq.Async
 {
@@ -16,6 +17,8 @@ internal interface IAwaitableFactory
 
 		object CreateFaulted(IEnumerable<Exception> exceptions);
 
+		Expression CreateResultExpression(Expression awaitableExpression);
+
 		bool TryGetResult(object awaitable, out object result);
 	}
 }

src/Moq/Async/TaskFactory.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq.Expressions;
 using System.Reflection;
 using System.Threading.Tasks;
 

src/Moq/Async/TaskFactory`1.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq.Expressions;
 using System.Threading.Tasks;
 
 namespace Moq.Async
@@ -28,6 +29,13 @@ public override Task<TResult> CreateFaulted(IEnumerable<Exception> exceptions)
 			return tcs.Task;
 		}
 
+		public override Expression CreateResultExpression(Expression awaitableExpression)
+		{
+			return Expression.MakeMemberAccess(
+				awaitableExpression,
+				typeof(Task<TResult>).GetProperty(nameof(Task<TResult>.Result)));
+		}
+
 		public override bool TryGetResult(Task<TResult> task, out TResult result)
 		{
 			if (task.Status == TaskStatus.RanToCompletion)

src/Moq/Async/ValueTaskFactory`1.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq.Expressions;
 using System.Threading.Tasks;
 
 namespace Moq.Async
@@ -28,6 +29,13 @@ public override ValueTask<TResult> CreateFaulted(IEnumerable<Exception> exceptio
 			return new ValueTask<TResult>(tcs.Task);
 		}
 
+		public override Expression CreateResultExpression(Expression awaitableExpression)
+		{
+			return Expression.MakeMemberAccess(
+				awaitableExpression,
+				typeof(ValueTask<TResult>).GetProperty(nameof(ValueTask<TResult>.Result)));
+		}
+
 		public override bool TryGetResult(ValueTask<TResult> valueTask, out TResult result)
 		{
 			if (valueTask.IsCompletedSuccessfully)