Improved async/await decompiler.

ICSharpCode.Decompiler/Ast/AstBuilder.cs

@@ -81,6 +81,8 @@ namespace ICSharpCode.Decompiler.Ast
 						return true;
 					if (settings.YieldReturn && YieldReturnDecompiler.IsCompilerGeneratorEnumerator(type))
 						return true;
+					if (settings.AsyncAwait && AsyncDecompiler.IsCompilerGeneratedStateMachine(type))
+						return true;
 				} else if (type.IsCompilerGenerated()) {
 					if (type.Name.StartsWith("<PrivateImplementationDetails>", StringComparison.Ordinal))
 						return true;
@@ -1357,6 +1359,12 @@ namespace ICSharpCode.Decompiler.Ast
 						// don't show the ParamArrayAttribute (it's converted to the 'params' modifier)
 						continue;
 					}
+					if (customAttribute.AttributeType.Name == "DebuggerStepThroughAttribute" && customAttribute.AttributeType.Namespace == "System.Diagnostics") {
+						// don't show the attribute if the method is async
+						EntityDeclaration entityDecl = attributedNode as EntityDeclaration;
+						if (entityDecl != null && entityDecl.HasModifier(Modifiers.Async))
+							continue;
+					}
 					
 					var attribute = new ICSharpCode.NRefactory.CSharp.Attribute();
 					attribute.AddAnnotation(customAttribute);

ICSharpCode.Decompiler/ILAst/AsyncDecompiler.cs

@@ -21,6 +21,7 @@ using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using Mono.Cecil;
+using Mono.Cecil.Cil;
 
 namespace ICSharpCode.Decompiler.ILAst
 {
@@ -29,6 +30,17 @@ namespace ICSharpCode.Decompiler.ILAst
 	/// </summary>
 	class AsyncDecompiler
 	{
+		public static bool IsCompilerGeneratedStateMachine(TypeDefinition type)
+		{
+			if (!(type.DeclaringType != null && type.IsCompilerGenerated()))
+				return false;
+			foreach (TypeReference i in type.Interfaces) {
+				if (i.Namespace == "System.Runtime.CompilerServices" && i.Name == "IAsyncStateMachine")
+					return true;
+			}
+			return false;
+		}
+		
 		enum AsyncMethodType
 		{
 			Void,
@@ -90,6 +102,7 @@ namespace ICSharpCode.Decompiler.ILAst
 			ValidateCatchBlock(mainTryCatch.CatchBlocks[0]);
 			AnalyzeStateMachine(mainTryCatch.TryBlock);
 			// AnalyzeStateMachine invokes ConvertBody
+			MarkGeneratedVariables();
 			YieldReturnDecompiler.TranslateFieldsToLocalAccess(newTopLevelBody, fieldToParameterMap);
 		}
 		#endregion
@@ -384,6 +397,7 @@ namespace ICSharpCode.Decompiler.ILAst
 					FieldDefinition awaiterField;
 					int targetStateID;
 					HandleAwait(newBody, out awaiterVar, out awaiterField, out targetStateID);
+					MarkAsGeneratedVariable(awaiterVar);
 					newBody.Add(new ILExpression(ILCode.Await, null, new ILExpression(ILCode.Ldloca, awaiterVar)));
 					newBody.Add(MakeGoTo(mapping, targetStateID));
 				} else if (tryCatchBlock != null) {
@@ -431,6 +445,10 @@ namespace ICSharpCode.Decompiler.ILAst
 					if (loadDoFinallyBodies.MatchLdloc(doFinallyBodies) && loadZero.Match(ILCode.Ldc_I4, out num) && num == 0) {
 						newBody.RemoveAt(0);
 					}
+				} else if (ceqExpr.Match(ILCode.LogicNot, out loadDoFinallyBodies)) {
+					if (loadDoFinallyBodies.MatchLdloc(doFinallyBodies)) {
+						newBody.RemoveAt(0);
+					}
 				}
 			}
 			return newBody;
@@ -481,6 +499,26 @@ namespace ICSharpCode.Decompiler.ILAst
 		}
 		#endregion
 		
+		#region MarkGeneratedVariables
+		int smallestGeneratedVariableIndex = int.MaxValue;
+		
+		void MarkAsGeneratedVariable(ILVariable v)
+		{
+			if (v.OriginalVariable != null && v.OriginalVariable.Index >= 0) {
+				smallestGeneratedVariableIndex = Math.Min(smallestGeneratedVariableIndex, v.OriginalVariable.Index);
+			}
+		}
+		
+		void MarkGeneratedVariables()
+		{
+			var expressions = new ILBlock(newTopLevelBody).GetSelfAndChildrenRecursive<ILExpression>();
+			foreach (var v in expressions.Select(e => e.Operand).OfType<ILVariable>()) {
+				if (v.OriginalVariable != null && v.OriginalVariable.Index >= smallestGeneratedVariableIndex)
+					v.IsGenerated = true;
+			}
+		}
+		#endregion
+		
 		#region RunStep2() method
 		public static void RunStep2(DecompilerContext context, ILBlock method)
 		{
@@ -524,6 +562,11 @@ namespace ICSharpCode.Decompiler.ILAst
 			if (!loadAwaiter.Match(ILCode.Ldloca, out awaiterVar))
 				return false;
 			
+			ILVariable stackVar;
+			ILExpression stackExpr;
+			while (pos >= 1 && body[pos - 1].Match(ILCode.Stloc, out stackVar, out stackExpr))
+				pos--;
+			
 			// stloc(CS$0$0001, callvirt(class System.Threading.Tasks.Task`1<bool>::GetAwaiter, awaiterExpr)
 			ILExpression getAwaiterCall;
 			if (!(pos >= 2 && body[pos - 2].MatchStloc(awaiterVar, out getAwaiterCall)))
@@ -552,6 +595,7 @@ namespace ICSharpCode.Decompiler.ILAst
 					case ILCode.Stloc:
 					case ILCode.Initobj:
 					case ILCode.Stfld:
+					case ILCode.Await:
 						// e.g.
 						// stloc(CS$0$0001, ldfld(StateMachine::<>u__$awaitere, ldloc(this)))
 						// initobj(valuetype [mscorlib]System.Runtime.CompilerServices.TaskAwaiter`1<bool>, ldloca(CS$0$0002_66))

ICSharpCode.Decompiler/ILAst/TypeAnalysis.cs

@@ -812,6 +812,14 @@ namespace ICSharpCode.Decompiler.ILAst
 						}
 					}
 					return null;
+				case ILCode.Await:
+					{
+						TypeReference taskType = InferTypeForExpression(expr.Arguments[0], null);
+						if (taskType.Name == "Task`1" && taskType.IsGenericInstance && taskType.Namespace == "System.Threading.Tasks") {
+							return ((GenericInstanceType)taskType).GenericArguments[0];
+						}
+						return null;
+					}
 					#endregion
 				case ILCode.Pop:
 					return null;

ICSharpCode.Decompiler/Tests/Async.cs

@@ -59,7 +59,8 @@ public class Async
 	public async void TwoAwaitsWithDifferentAwaiterTypes()
 	{
 		Console.WriteLine("Before");
-		if (await SimpleBoolTaskMethod()) {
+		if (await this.SimpleBoolTaskMethod()) 
+		{
 			await Task.Delay(TimeSpan.FromSeconds(1.0));
 		}
 		Console.WriteLine("After");
@@ -77,27 +78,33 @@ public class Async
 	
 	public async void AwaitInLoopCondition()
 	{
-		while (await SimpleBoolTaskMethod()) {
+		while (await this.SimpleBoolTaskMethod()) 
+		{
 			Console.WriteLine("Body");
 		}
 	}
 	
 	public async Task<int> AwaitInForEach(IEnumerable<Task<int>> elements)
 	{
-		int sum = 0;
+		int num = 0;
-		foreach (Task<int> element in elements) {
+		foreach (Task<int> current in elements)
-			sum += await element;
+		{
+			num += await current;
 		}
-		return sum;
+		return num;
 	}
 	
 	public async Task TaskMethodWithoutAwaitButWithExceptionHandling()
 	{
-		try {
+		try 
-			using (new StringWriter()) {
+		{
+			using (new StringWriter())
+			{
 				Console.WriteLine("No Await");
 			}
-		} catch (Exception) {
+		} 
+		catch (Exception) 
+		{
 			Console.WriteLine("Crash");
 		}
 	}
@@ -106,4 +113,22 @@ public class Async
 	{
 		return await(await task);
 	}
+	
+	public async Task AwaitWithStack(Task<int> task)
+	{
+		Console.WriteLine("A", 1, await task);
+	}
+	
+	public async Task AwaitWithStack2(Task<int> task)
+	{
+		if (await this.SimpleBoolTaskMethod()) 
+		{
+			Console.WriteLine("A", 1, await task);
+		} 
+		else 
+		{
+			int num = 1;
+			Console.WriteLine("A", 1, num);
+		}
+	}
 }

ICSharpCode.Decompiler/Tests/TestRunner.cs

@@ -34,6 +34,12 @@ namespace ICSharpCode.Decompiler.Tests
 	[TestFixture]
 	public class TestRunner
 	{
+		[Test]
+		public void Async()
+		{
+			TestFile(@"..\..\Tests\Async.cs");
+		}
+		
 		[Test, Ignore("disambiguating overloads is not yet implemented")]
 		public void CallOverloadedMethod()
 		{

ILSpy/Languages/ILAstLanguage.cs

@@ -71,6 +71,9 @@ namespace ICSharpCode.ILSpy
 						output.Write("pinned ");
 					v.Type.WriteTo(output, ILNameSyntax.ShortTypeName);
 				}
+				if (v.IsGenerated) {
+					output.Write(" [generated]");
+				}
 				output.WriteLine();
 			}
 			output.WriteLine();