Fix #1604: async methods that had no 'await' but were capturing 'this' were not decompiled correctly

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Async.cs

@@ -26,6 +26,8 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 {
 	public class Async
 	{
+		private int memberField;
+
 		public async void SimpleVoidMethod()
 		{
 			Console.WriteLine("Before");
@@ -72,6 +74,16 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			Console.WriteLine("No Await");
 		}
 
+		public async Task CapturingThis()
+		{
+			await Task.Delay(memberField);
+		}
+
+		public async Task CapturingThisWithoutAwait()
+		{
+			Console.WriteLine(memberField);
+		}
+
 		public async Task<bool> SimpleBoolTaskMethod()
 		{
 			Console.WriteLine("Before");

ICSharpCode.Decompiler/IL/ControlFlow/AsyncAwaitDecompiler.cs

@@ -355,27 +355,22 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			if (blockContainer.EntryPoint.IncomingEdgeCount != 1)
 				throw new SymbolicAnalysisFailedException();
 			int pos = 0;
-			if (blockContainer.EntryPoint.Instructions[0].MatchStLoc(out cachedStateVar, out var cachedStateInit)) {
-				// stloc(cachedState, ldfld(valuetype StateMachineStruct::<>1__state, ldloc(this)))
-				if (!cachedStateInit.MatchLdFld(out var target, out var loadedField))
-					throw new SymbolicAnalysisFailedException();
-				if (!target.MatchLdThis())
-					throw new SymbolicAnalysisFailedException();
-				if (loadedField.MemberDefinition != stateField)
-					throw new SymbolicAnalysisFailedException();
-				++pos;
-			}
 			while (blockContainer.EntryPoint.Instructions[pos] is StLoc stloc) {
 				// stloc V_1(ldfld <>4__this(ldloc this))
-				if (!stloc.Variable.IsSingleDefinition)
-					throw new SymbolicAnalysisFailedException();
 				if (!stloc.Value.MatchLdFld(out var target, out var field))
 					throw new SymbolicAnalysisFailedException();
 				if (!target.MatchLdThis())
 					throw new SymbolicAnalysisFailedException();
-				if (!fieldToParameterMap.TryGetValue((IField)field.MemberDefinition, out var param))
+				if (field.MemberDefinition == stateField) {
+					// stloc(cachedState, ldfld(valuetype StateMachineStruct::<>1__state, ldloc(this)))
+					cachedStateVar = stloc.Variable;
+				} else if (fieldToParameterMap.TryGetValue((IField)field.MemberDefinition, out var param)) {
+					if (!stloc.Variable.IsSingleDefinition)
+						throw new SymbolicAnalysisFailedException();
+					cachedFieldToParameterMap[stloc.Variable] = param;
+				} else {
 					throw new SymbolicAnalysisFailedException();
-				cachedFieldToParameterMap[stloc.Variable] = param;
+				}
 				pos++;
 			}
 			mainTryCatch = blockContainer.EntryPoint.Instructions[pos] as TryCatch;