Initial support for `async IAsyncEnumerator<T>` methods

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -305,6 +305,8 @@ namespace ICSharpCode.Decompiler.CSharp
 							return true;
 						if (settings.AsyncAwait && AsyncAwaitDecompiler.IsCompilerGeneratedStateMachine(typeHandle, metadata))
 							return true;
+						if (settings.AsyncEnumerator && AsyncAwaitDecompiler.IsCompilerGeneratorAsyncEnumerator(typeHandle, metadata))
+							return true;
 						if (settings.FixedBuffers && name.StartsWith("<", StringComparison.Ordinal) && name.Contains("__FixedBuffer"))
 							return true;
 					} else if (type.IsCompilerGenerated(metadata)) {

ICSharpCode.Decompiler/DecompilerSettings.cs

@@ -108,12 +108,13 @@ namespace ICSharpCode.Decompiler
 			if (languageVersion < CSharp.LanguageVersion.CSharp8_0) {
 				nullableReferenceTypes = false;
 				readOnlyMethods = false;
+				asyncEnumerator = false;
 			}
 		}
 
 		public CSharp.LanguageVersion GetMinimumRequiredVersion()
 		{
-			if (nullableReferenceTypes || readOnlyMethods)
+			if (nullableReferenceTypes || readOnlyMethods || asyncEnumerator)
 				return CSharp.LanguageVersion.CSharp8_0;
 			if (introduceUnmanagedConstraint || tupleComparisons || stackAllocInitializers)
 				return CSharp.LanguageVersion.CSharp7_3;
@@ -273,6 +274,24 @@ namespace ICSharpCode.Decompiler
 			}
 		}
 
+		bool asyncEnumerator = true;
+
+		/// <summary>
+		/// Decompile IAsyncEnumerator/IAsyncEnumerable.
+		/// Only has an effect if <see cref="AsyncAwait"/> is enabled.
+		/// </summary>
+		[Category("C# 8.0 / VS 2019")]
+		[Description("DecompilerSettings.AsyncEnumerator")]
+		public bool AsyncEnumerator {
+			get { return asyncEnumerator; }
+			set {
+				if (asyncEnumerator != value) {
+					asyncEnumerator = value;
+					OnPropertyChanged();
+				}
+			}
+		}
+
 		bool decimalConstants = true;
 
 		/// <summary>
@@ -846,7 +865,7 @@ namespace ICSharpCode.Decompiler
 		bool readOnlyMethods = true;
 
 		[Category("C# 8.0 / VS 2019")]
-		[Description("DecompilerSettings.IsReadOnlyAttributeShouldBeReplacedWithReadonlyInModifiersOnStructsParameters")]
+		[Description("DecompilerSettings.ReadOnlyMethods")]
 		public bool ReadOnlyMethods {
 			get { return readOnlyMethods; }
 			set {

ICSharpCode.Decompiler/IL/ControlFlow/AsyncAwaitDecompiler.cs

@@ -62,14 +62,16 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		{
 			Void,
 			Task,
-			TaskOfT
+			TaskOfT,
+			AsyncEnumerator,
+			AsyncEnumerable
 		}
 
 		ILTransformContext context;
 
-		// These fields are set by MatchTaskCreationPattern()
-		IType taskType; // return type of the async method
-		IType underlyingReturnType; // return type of the method (only the "T" for Task{T})
+		// These fields are set by MatchTaskCreationPattern() or MatchEnumeratorCreationNewObj()
+		IType taskType; // return type of the async method; or IAsyncEnumerable{T}/IAsyncEnumerator{T}
+		IType underlyingReturnType; // return type of the method (only the "T" for Task{T}), for async enumerators this is the type being yielded
 		AsyncMethodType methodType;
 		ITypeDefinition stateMachineType;
 		ITypeDefinition builderType;
@@ -84,9 +86,11 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		ILVariable cachedStateVar; // variable in MoveNext that caches the stateField.
 		TryCatch mainTryCatch;
 		Block setResultAndExitBlock; // block that is jumped to for return statements
+									 // Note: for async enumerators, a jump to setResultAndExitBlock is a 'yield break;'
 		int finalState;       // final state after the setResultAndExitBlock
 		bool finalStateKnown;
 		ILVariable resultVar; // the variable that gets returned by the setResultAndExitBlock
+		Block setResultYieldBlock; // block that is jumped to for 'yield return' statements
 		ILVariable doFinallyBodies;
 
 		// These fields are set by AnalyzeStateMachine():
@@ -110,7 +114,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			awaitBlocks.Clear();
 			awaitDebugInfos.Clear();
 			moveNextLeaves.Clear();
-			if (!MatchTaskCreationPattern(function))
+			if (!MatchTaskCreationPattern(function) && !MatchAsyncEnumeratorCreationPattern(function))
 				return;
 			try {
 				AnalyzeMoveNext();
@@ -133,7 +137,11 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			TranslateCachedFieldsToLocals();
 
 			FinalizeInlineMoveNext(function);
+			if (methodType == AsyncMethodType.AsyncEnumerable || methodType == AsyncMethodType.AsyncEnumerator) {
+				((BlockContainer)function.Body).ExpectedResultType = StackType.Void;
+			} else {
 				((BlockContainer)function.Body).ExpectedResultType = underlyingReturnType.GetStackType();
+			}
 
 			// Re-run control flow simplification over the newly constructed set of gotos,
 			// and inlining because TranslateFieldsToLocalAccess() might have opened up new inlining opportunities.
@@ -337,6 +345,118 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		}
 		#endregion
 
+		#region MatchAsyncEnumeratorCreationPattern
+		private bool MatchAsyncEnumeratorCreationPattern(ILFunction function)
+		{
+			if (!context.Settings.AsyncEnumerator)
+				return false;
+			taskType = function.ReturnType;
+			if (taskType.IsKnownType(KnownTypeCode.IAsyncEnumeratorOfT)) {
+				methodType = AsyncMethodType.AsyncEnumerator;
+			} else if (taskType.IsKnownType(KnownTypeCode.IAsyncEnumerableOfT)) {
+				methodType = AsyncMethodType.AsyncEnumerable;
+			} else {
+				return false;
+			}
+			underlyingReturnType = taskType.TypeArguments.Single();
+			if (!(function.Body is BlockContainer blockContainer))
+				return false;
+			if (blockContainer.Blocks.Count != 1)
+				return false;
+			var body = blockContainer.EntryPoint;
+			if (body.Instructions.Count == 1) {
+				// No parameters passed to enumerator (not even 'this'):
+				// ret(newobj(...))
+				if (!body.Instructions[0].MatchReturn(out var newObj))
+					return false;
+				if (MatchEnumeratorCreationNewObj(newObj, context, out initialState, out stateMachineType)) {
+					// HACK: the normal async/await logic expects 'initialState' to be the 'in progress' state
+					initialState = -1;
+					try {
+						AnalyzeEnumeratorCtor(((NewObj)newObj).Method, context, out builderField, out stateField);
+					} catch (SymbolicAnalysisFailedException) {
+						return false;
+					}
+					builderType = builderField.Type.GetDefinition();
+					if (builderType == null)
+						return false;
+					return true;
+				} else {
+					return false;
+				}
+			}
+			// TODO: enumerator creation with parameters
+			return false;
+		}
+
+		static bool MatchEnumeratorCreationNewObj(ILInstruction inst, ILTransformContext context,
+			out int initialState, out ITypeDefinition stateMachineType)
+		{
+			initialState = default;
+			stateMachineType = default;
+			// newobj(CurrentType/...::.ctor, ldc.i4(-2))
+			if (!(inst is NewObj newObj))
+				return false;
+			if (newObj.Arguments.Count != 1)
+				return false;
+			if (!newObj.Arguments[0].MatchLdcI4(out initialState))
+				return false;
+			stateMachineType = newObj.Method.DeclaringTypeDefinition;
+			if (stateMachineType == null)
+				return false;
+			if (stateMachineType.DeclaringTypeDefinition != context.Function.Method.DeclaringTypeDefinition)
+				return false;
+			return IsCompilerGeneratorAsyncEnumerator(
+				(TypeDefinitionHandle)stateMachineType.MetadataToken,
+				context.TypeSystem.MainModule.metadata);
+		}
+
+		public static bool IsCompilerGeneratorAsyncEnumerator(TypeDefinitionHandle type, MetadataReader metadata)
+		{
+			TypeDefinition td;
+			if (type.IsNil || !type.IsCompilerGeneratedOrIsInCompilerGeneratedClass(metadata) || (td = metadata.GetTypeDefinition(type)).GetDeclaringType().IsNil)
+				return false;
+			foreach (var i in td.GetInterfaceImplementations()) {
+				var tr = metadata.GetInterfaceImplementation(i).Interface.GetFullTypeName(metadata);
+				if (!tr.IsNested && tr.TopLevelTypeName.Namespace == "System.Collections.Generic" && tr.TopLevelTypeName.Name == "IAsyncEnumerator" && tr.TopLevelTypeName.TypeParameterCount == 1)
+					return true;
+			}
+			return false;
+		}
+
+		static void AnalyzeEnumeratorCtor(IMethod ctor, ILTransformContext context, out IField builderField, out IField stateField)
+		{
+			builderField = null;
+			stateField = null;
+
+			var ctorHandle = (MethodDefinitionHandle)ctor.MetadataToken;
+			Block body = YieldReturnDecompiler.SingleBlock(YieldReturnDecompiler.CreateILAst(ctorHandle, context).Body);
+			if (body == null)
+				throw new SymbolicAnalysisFailedException("Missing enumeratorCtor.Body");
+			// Block IL_0000 (incoming: 1) {
+			//   call Object..ctor(ldloc this)
+			// 	 stfld <>1__state(ldloc this, ldloc <>1__state)
+			// 	 stfld <>t__builder(ldloc this, call Create())
+			// 	 leave IL_0000 (nop)
+			// }
+			if (body.Instructions.ElementAtOrDefault(1).MatchStFld(out var target, out var field, out var value)
+				&& target.MatchLdThis()
+				&& value.MatchLdLoc(out var arg)
+				&& arg.Kind == VariableKind.Parameter && arg.Index == 0) {
+				stateField = (IField)field.MemberDefinition;
+			} else {
+				throw new SymbolicAnalysisFailedException("Could not find stateField");
+			}
+			if (body.Instructions.ElementAtOrDefault(2).MatchStFld(out target, out field, out value)
+				&& target.MatchLdThis()
+				&& value is Call call && call.Method.Name == "Create") {
+				builderField = (IField)field.MemberDefinition;
+			} else {
+				throw new SymbolicAnalysisFailedException("Could not find builderField");
+			}
+		}
+		#endregion
+
 		#region AnalyzeMoveNext
 		/// <summary>
 		/// First peek into MoveNext(); analyzes everything outside the big try-catch.
@@ -353,8 +473,6 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			moveNextFunction = YieldReturnDecompiler.CreateILAst(moveNextMethod, context);
 			if (!(moveNextFunction.Body is BlockContainer blockContainer))
 				throw new SymbolicAnalysisFailedException();
-			if (blockContainer.Blocks.Count != 2 && blockContainer.Blocks.Count != 1)
-				throw new SymbolicAnalysisFailedException();
 			if (blockContainer.EntryPoint.IncomingEdgeCount != 1)
 				throw new SymbolicAnalysisFailedException();
 			cachedStateVar = null;
@@ -385,12 +503,49 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			if (((BlockContainer)mainTryCatch.TryBlock).EntryPoint.Instructions[0] is StLoc initDoFinallyBodies
 				&& initDoFinallyBodies.Variable.Kind == VariableKind.Local
 				&& initDoFinallyBodies.Variable.Type.IsKnownType(KnownTypeCode.Boolean)
-				&& initDoFinallyBodies.Value.MatchLdcI4(1))
-			{
+				&& initDoFinallyBodies.Value.MatchLdcI4(1)) {
 				doFinallyBodies = initDoFinallyBodies.Variable;
 			}
 
-			setResultAndExitBlock = blockContainer.Blocks.ElementAtOrDefault(1);
+			Debug.Assert(blockContainer.Blocks[0] == blockContainer.EntryPoint); // already checked this block
+			pos = 1;
+			if (MatchYieldBlock(blockContainer, pos)) {
+				setResultYieldBlock = blockContainer.Blocks[pos];
+				pos++;
+			} else {
+				setResultYieldBlock = null;
+			}
+
+			setResultAndExitBlock = blockContainer.Blocks.ElementAtOrDefault(pos);
+			CheckSetResultAndExitBlock(blockContainer);
+
+			if (pos + 1 < blockContainer.Blocks.Count)
+				throw new SymbolicAnalysisFailedException("too many blocks");
+		}
+
+		private bool IsAsyncEnumerator => methodType == AsyncMethodType.AsyncEnumerable || methodType == AsyncMethodType.AsyncEnumerator;
+
+		bool MatchYieldBlock(BlockContainer blockContainer, int pos)
+		{
+			if (!IsAsyncEnumerator)
+				return false;
+			var block = blockContainer.Blocks.ElementAtOrDefault(pos);
+			// call SetResult(ldflda <>v__promiseOfValueOrEnd(ldloc this), ldc.i4 1)
+			// leave IL_0000(nop)
+			if (block.Instructions.Count != 2)
+				return false;
+			if (!MatchCall(block.Instructions[0], "SetResult", out var args))
+				return false;
+			if (args.Count != 2)
+				return false;
+			if (!IsBuilderOrPromiseFieldOnThis(args[0]))
+				return false;
+			if (!args[1].MatchLdcI4(1))
+				return false;
+			return block.Instructions[1].MatchLeave(blockContainer);
+		}
+		void CheckSetResultAndExitBlock(BlockContainer blockContainer)
+		{
 			if (setResultAndExitBlock == null) {
 				// This block can be absent if the function never exits normally,
 				// but always throws an exception/loops infinitely.
@@ -408,17 +563,29 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			finalStateKnown = true;
 			if (!MatchCall(setResultAndExitBlock.Instructions[1], "SetResult", out var args))
 				throw new SymbolicAnalysisFailedException();
-			if (!IsBuilderFieldOnThis(args[0]))
+			if (!IsBuilderOrPromiseFieldOnThis(args[0]))
 				throw new SymbolicAnalysisFailedException();
-			if (methodType == AsyncMethodType.TaskOfT) {
+			switch (methodType) {
+				case AsyncMethodType.TaskOfT:
 					if (args.Count != 2)
 						throw new SymbolicAnalysisFailedException();
 					if (!args[1].MatchLdLoc(out resultVar))
 						throw new SymbolicAnalysisFailedException();
-			} else {
+					break;
+				case AsyncMethodType.Task:
+				case AsyncMethodType.Void:
 					resultVar = null;
 					if (args.Count != 1)
 						throw new SymbolicAnalysisFailedException();
+					break;
+				case AsyncMethodType.AsyncEnumerable:
+				case AsyncMethodType.AsyncEnumerator:
+					resultVar = null;
+					if (args.Count != 2)
+						throw new SymbolicAnalysisFailedException();
+					if (!args[1].MatchLdcI4(0))
+						throw new SymbolicAnalysisFailedException();
+					break;
 			}
 			if (!setResultAndExitBlock.Instructions[2].MatchLeave(blockContainer))
 				throw new SymbolicAnalysisFailedException();
@@ -465,7 +632,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				throw new SymbolicAnalysisFailedException();
 			if (args.Count != 2)
 				throw new SymbolicAnalysisFailedException();
-			if (!IsBuilderFieldOnThis(args[0]))
+			if (!IsBuilderOrPromiseFieldOnThis(args[0]))
 				throw new SymbolicAnalysisFailedException();
 			if (!args[1].MatchLdLoc(stloc.Variable))
 				throw new SymbolicAnalysisFailedException();
@@ -490,13 +657,22 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			return target.MatchLdThis() && field.MemberDefinition == builderField;
 		}
 
+		bool IsBuilderOrPromiseFieldOnThis(ILInstruction inst)
+		{
+			if (methodType == AsyncMethodType.AsyncEnumerable || methodType == AsyncMethodType.AsyncEnumerator) {
+				return true; // TODO: check against uses of promise fields in other methods?
+			} else {
+				return IsBuilderFieldOnThis(inst);
+			}
+		}
+
 		bool MatchStateAssignment(ILInstruction inst, out int newState)
 		{
 			// stfld(StateMachine::<>1__state, ldloc(this), ldc.i4(stateId))
 			if (inst.MatchStFld(out var target, out var field, out var value)
-				&& target.MatchLdThis()
+				&& StackSlotValue(target).MatchLdThis()
 				&& field.MemberDefinition == stateField
-				&& value.MatchLdcI4(out newState))
+				&& StackSlotValue(value).MatchLdcI4(out newState))
 			{
 				return true;
 			}
@@ -520,6 +696,10 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 					branch.ReplaceWith(new Leave((BlockContainer)function.Body, resultVar == null ? null : new LdLoc(resultVar)).WithILRange(branch));
 				}
 			}
+			if (setResultYieldBlock != null) {
+				// We still might have branches to this block; and we can't quite yet get rid of it.
+				((BlockContainer)function.Body).Blocks.Add(setResultYieldBlock);
+			}
 			foreach (var leave in function.Descendants.OfType<Leave>()) {
 				if (leave.TargetContainer == moveNextFunction.Body) {
 					leave.TargetContainer = (BlockContainer)function.Body;
@@ -591,6 +771,19 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 								smallestAwaiterVarIndex = awaiterVar.Index.Value;
 							}
 						}
+					} else if (block.Instructions.Last().MatchBranch(setResultYieldBlock)) {
+						// This is a 'yield' in an async enumerator.
+						if (AnalyzeYieldReturn(block, out var yieldValue, out int state)) {
+							block.Instructions.Add(new YieldReturn(yieldValue));
+							Block targetBlock = stateToBlockMap.GetOrDefault(state);
+							if (targetBlock != null) {
+								block.Instructions.Add(new Branch(targetBlock));
+							} else {
+								block.Instructions.Add(new InvalidBranch("Could not find block for state " + state));
+							}
+						} else {
+							block.Instructions.Add(new InvalidBranch("Could not detect 'yield return'"));
+						}
 					}
 				}
 				// Skip the state dispatcher and directly jump to the initial state
@@ -606,6 +799,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			}
 		}
 
+
 		bool AnalyzeAwaitBlock(Block block, out ILVariable awaiter, out IField awaiterField, out int state, out int yieldOffset)
 		{
 			awaiter = null;
@@ -705,6 +899,49 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			}
 			return inst;
 		}
+
+		private bool AnalyzeYieldReturn(Block block, out ILInstruction yieldValue, out int newState)
+		{
+			yieldValue = default;
+			newState = default;
+			Debug.Assert(block.Instructions.Last().MatchBranch(setResultYieldBlock));
+			// stfld current(ldloc this, ldstr "yieldValue")
+			// stloc S_45(ldloc this)
+			// stloc S_46(ldc.i4 -5)
+			// stloc V_0(ldloc S_46)
+			// stfld stateField(ldloc S_45, ldloc S_46)
+			// br setResultYieldBlock
+
+			int pos = block.Instructions.Count - 2;
+			// Immediately before the 'yield return', there should be a state assignment:
+			if (pos < 0 || !MatchStateAssignment(block.Instructions[pos], out newState))
+				return false;
+			pos--;
+
+			if (pos >= 0 && block.Instructions[pos].MatchStLoc(cachedStateVar, out var cachedStateNewValue)) {
+				if (StackSlotValue(cachedStateNewValue).MatchLdcI4(newState)) {
+					pos--; // OK, ignore V_0 store
+				} else {
+					return false;
+				}
+			}
+
+			while (pos >= 0 && block.Instructions[pos] is StLoc stloc) {
+				if (stloc.Variable.Kind != VariableKind.StackSlot)
+					return false;
+				if (!SemanticHelper.IsPure(stloc.Value.Flags))
+					return false;
+			}
+
+			if (pos < 0 || !block.Instructions[pos].MatchStFld(out var target, out var field, out yieldValue))
+				return false;
+			if (!StackSlotValue(target).MatchLdThis())
+				return false;
+			// TODO: check that we are accessing the current field (compare with get_Current)
+
+			block.Instructions.RemoveRange(pos, block.Instructions.Count - pos);
+			return true;
+		}
 		#endregion
 
 		#region DetectAwaitPattern

ICSharpCode.Decompiler/IL/ControlFlow/AwaitInCatchTransform.cs

@@ -197,6 +197,8 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 	{
 		public static void Run(ILFunction function, ILTransformContext context)
 		{
+			if (!context.Settings.AwaitInCatchFinally)
+				return;
 			HashSet<BlockContainer> changedContainers = new HashSet<BlockContainer>();
 
 			// analyze all try-catch statements in the function

ICSharpCode.Decompiler/IL/ControlFlow/YieldReturnDecompiler.cs

@@ -305,6 +305,16 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		/// </summary>
 		bool MatchEnumeratorCreationNewObj(ILInstruction inst)
 		{
+			return MatchEnumeratorCreationNewObj(inst, metadata, currentType,
+				out enumeratorCtor, out enumeratorType);
+		}
+
+		internal static bool MatchEnumeratorCreationNewObj(ILInstruction inst, 
+			MetadataReader metadata, TypeDefinitionHandle currentType,
+			out MethodDefinitionHandle enumeratorCtor, out TypeDefinitionHandle enumeratorType)
+		{
+			enumeratorCtor = default;
+			enumeratorType = default;
 			// newobj(CurrentType/...::.ctor, ldc.i4(-2))
 			if (!(inst is NewObj newObj))
 				return false;

ILSpy/Properties/Resources.Designer.cs

@@ -556,6 +556,15 @@ namespace ICSharpCode.ILSpy.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Decompile async IAsyncEnumerator methods.
+        /// </summary>
+        public static string DecompilerSettings_AsyncEnumerator {
+            get {
+                return ResourceManager.GetString("DecompilerSettings.AsyncEnumerator", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Decompile ?. and ?[] operators.
         /// </summary>
@@ -810,6 +819,15 @@ namespace ICSharpCode.ILSpy.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Read-only methods.
+        /// </summary>
+        public static string DecompilerSettings_ReadOnlyMethods {
+            get {
+                return ResourceManager.GetString("DecompilerSettings.ReadOnlyMethods", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Remove dead and side effect free code (use with caution!).
         /// </summary>

ILSpy/Properties/Resources.resx

@@ -769,4 +769,10 @@ Are you sure you want to continue?</value>
   <data name="DecompileToNewPanel" xml:space="preserve">
     <value>Decompile to new tab</value>
   </data>
+  <data name="DecompilerSettings.AsyncEnumerator" xml:space="preserve">
+    <value>Decompile async IAsyncEnumerator methods</value>
+  </data>
+  <data name="DecompilerSettings.ReadOnlyMethods" xml:space="preserve">
+    <value>Read-only methods</value>
+  </data>
 </root>