Add support for C# 8.0 await foreach

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -94,6 +94,7 @@
     <Compile Include="TestAssemblyResolver.cs" />
     <Compile Include="TestCases\Correctness\DeconstructionTests.cs" />
     <Compile Include="TestCases\Correctness\StringConcat.cs" />
+    <None Include="TestCases\Pretty\AsyncForeach.cs" />
     <Compile Include="TestCases\Pretty\DeconstructionTests.cs" />
     <Compile Include="TestCases\ILPretty\Issue2104.cs" />
     <Compile Include="TestCases\Pretty\SwitchExpressions.cs" />

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -314,6 +314,12 @@ namespace ICSharpCode.Decompiler.Tests
 			RunForLibrary(cscOptions: cscOptions);
 		}
 
+		[Test]
+		public void AsyncForeach([ValueSource(nameof(dotnetCoreOnlyOptions))] CompilerOptions cscOptions)
+		{
+			RunForLibrary(cscOptions: cscOptions);
+		}
+
 		[Test]
 		public void AsyncMain([ValueSource(nameof(roslynOnlyOptions))] CompilerOptions cscOptions)
 		{

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

@@ -0,0 +1,32 @@
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	internal class AsyncForeach
+	{
+		public async Task<int> SumIntegers(IAsyncEnumerable<int> items, CancellationToken token)
+		{
+			int sum = 0;
+			await foreach (int item in items.WithCancellation(token)) {
+				if (token.IsCancellationRequested) {
+					break;
+				}
+				sum += item;
+			}
+			return sum;
+		}
+
+		public async Task<int> MaxInteger(IAsyncEnumerable<int> items)
+		{
+			int max = int.MinValue;
+			await foreach (int item in items) {
+				if (item > max) {
+					max = item;
+				}
+			}
+			return max;
+		}
+	}
+}

ICSharpCode.Decompiler/CSharp/OutputVisitor/CSharpOutputVisitor.cs

@@ -1556,6 +1556,8 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 		public virtual void VisitForeachStatement(ForeachStatement foreachStatement)
 		{
 			StartNode(foreachStatement);
+			if (foreachStatement.IsAsync)
+				WriteKeyword(ForeachStatement.AwaitRole);
 			WriteKeyword(ForeachStatement.ForeachKeywordRole);
 			Space(policy.SpaceBeforeForeachParentheses);
 			LPar();

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -403,8 +403,16 @@ namespace ICSharpCode.Decompiler.CSharp
 		}
 
 		#region foreach construction
-		static readonly InvocationExpression getEnumeratorPattern = new InvocationExpression(new MemberReferenceExpression(new AnyNode("collection").ToExpression(), "GetEnumerator"));
-		static readonly InvocationExpression moveNextConditionPattern = new InvocationExpression(new MemberReferenceExpression(new NamedNode("enumerator", new IdentifierExpression(Pattern.AnyString)), "MoveNext"));
+		static readonly InvocationExpression getEnumeratorPattern = new InvocationExpression(
+			new Choice {
+				new MemberReferenceExpression(new AnyNode("collection").ToExpression(), "GetEnumerator"),
+				new MemberReferenceExpression(new AnyNode("collection").ToExpression(), "GetAsyncEnumerator")
+			}
+		);
+		static readonly Expression moveNextConditionPattern = new Choice {
+			new InvocationExpression(new MemberReferenceExpression(new NamedNode("enumerator", new IdentifierExpression(Pattern.AnyString)), "MoveNext")),
+			new UnaryOperatorExpression(UnaryOperatorType.Await, new InvocationExpression(new MemberReferenceExpression(new NamedNode("enumerator", new IdentifierExpression(Pattern.AnyString)), "MoveNextAsync")))
+		};
 
 		protected internal override TranslatedStatement VisitUsingInstruction(UsingInstruction inst)
 		{
@@ -484,6 +492,9 @@ namespace ICSharpCode.Decompiler.CSharp
 			// The using body must be a BlockContainer.
 			if (!(inst.Body is BlockContainer container) || !m.Success)
 				return null;
+			bool isAsync = ((MemberReferenceExpression)((InvocationExpression)resource).Target).MemberName == "GetAsyncEnumerator";
+			if (isAsync != inst.IsAsync)
+				return null;
 			// The using-variable is the enumerator.
 			var enumeratorVar = inst.Variable;
 			// If there's another BlockContainer nested in this container and it only has one child block, unwrap it.
@@ -499,6 +510,8 @@ namespace ICSharpCode.Decompiler.CSharp
 			var m2 = moveNextConditionPattern.Match(condition.Expression);
 			if (!m2.Success)
 				return null;
+			if (condition.Expression is UnaryOperatorExpression { Operator: UnaryOperatorType.Await } != isAsync)
+				return null;
 			// Check enumerator variable references.
 			var enumeratorVar2 = m2.Get<IdentifierExpression>("enumerator").Single().GetILVariable();
 			if (enumeratorVar2 != enumeratorVar)
@@ -604,6 +617,7 @@ namespace ICSharpCode.Decompiler.CSharp
 
 			// Construct the foreach loop.
 			var foreachStmt = new ForeachStatement {
+				IsAsync = isAsync,
 				VariableType = useVar ? new SimpleType("var") : exprBuilder.ConvertType(foreachVariable.Type),
 				VariableDesignation = designation,
 				InExpression = collectionExpr.Detach(),

ICSharpCode.Decompiler/CSharp/Syntax/Statements/ForeachStatement.cs

@@ -32,9 +32,19 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 	/// </summary>
 	public class ForeachStatement : Statement
 	{
+		public static readonly TokenRole AwaitRole = UnaryOperatorExpression.AwaitRole;
 		public static readonly TokenRole ForeachKeywordRole = new TokenRole ("foreach");
 		public static readonly TokenRole InKeywordRole = new TokenRole ("in");
-		
+
+		public CSharpTokenNode AwaitToken {
+			get { return GetChildByRole(AwaitRole); }
+		}
+
+		public bool IsAsync {
+			get { return !GetChildByRole(AwaitRole).IsNull; }
+			set { SetChildByRole(AwaitRole, value ? new CSharpTokenNode(TextLocation.Empty, null) : null); }
+		}
+
 		public CSharpTokenNode ForeachToken {
 			get { return GetChildByRole (ForeachKeywordRole); }
 		}

ICSharpCode.Decompiler/IL/Transforms/UsingTransform.cs

@@ -293,7 +293,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						if (!UnwrapAwait(ref checkInst))
 							return false;
 					}
-					if (!(checkInst is CallVirt cv))
+					if (!(checkInst is CallInstruction cv))
 						return false;
 					target = cv.Arguments.FirstOrDefault();
 					if (target == null)
@@ -345,7 +345,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			if (i < 1 || !context.Settings.AsyncUsingAndForEachStatement) return false;
 			if (!(block.Instructions[i] is TryFinally tryFinally) || !(block.Instructions[i - 1] is StLoc storeInst))
 				return false;
-			if (!CheckAsyncResourceType(storeInst.Variable.Type))
+			if (!CheckAsyncResourceType(storeInst.Variable.Type, out string disposeMethodFullName))
 				return false;
 			if (storeInst.Variable.Kind != VariableKind.Local)
 				return false;
@@ -355,7 +355,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return false;
 			if (storeInst.Variable.StoreInstructions.Count > 1)
 				return false;
-			if (!(tryFinally.FinallyBlock is BlockContainer container) || !MatchDisposeBlock(container, storeInst.Variable, usingNull: false, "System.IAsyncDisposable.DisposeAsync", KnownTypeCode.IAsyncDisposable))
+			if (!(tryFinally.FinallyBlock is BlockContainer container) || !MatchDisposeBlock(container, storeInst.Variable, usingNull: false, disposeMethodFullName, KnownTypeCode.IAsyncDisposable))
 				return false;
 			context.Step("AsyncUsingTransform", tryFinally);
 			storeInst.Variable.Kind = VariableKind.UsingLocal;
@@ -365,10 +365,23 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool CheckAsyncResourceType(IType type)
+		bool CheckAsyncResourceType(IType type, out string disposeMethodFullName)
 		{
-			if (NullableType.GetUnderlyingType(type).GetAllBaseTypes().Any(b => b.IsKnownType(KnownTypeCode.IAsyncDisposable)))
+			disposeMethodFullName = null;
+			IType t = NullableType.GetUnderlyingType(type);
+			if (t.GetAllBaseTypes().Any(b => b.IsKnownType(KnownTypeCode.IAsyncDisposable))) {
+				disposeMethodFullName = "System.IAsyncDisposable.DisposeAsync";
 				return true;
+			}
+
+			IMethod disposeMethod = t
+				.GetMethods(m => m.Parameters.Count == 0 && m.TypeParameters.Count == 0 && m.Name == "DisposeAsync")
+				.SingleOrDefault();
+			if (disposeMethod != null) {
+				disposeMethodFullName = disposeMethod.FullName;
+				return true;
+			}
+
 			return false;
 		}
 
@@ -380,8 +393,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return false;
 			if (!arg.MatchAddressOf(out awaitInstruction, out var type))
 				return false;
-			if (!type.IsKnownType(KnownTypeCode.ValueTask))
-				return false;
+			// TODO check type: does it match the structural 'Awaitable' pattern?
 			return true;
 		}
 	}