Merge pull request #3731 from siegfriedpammer/runtime-async

ICSharpCode.Decompiler.Tests/Helpers/Tester.cs

@@ -73,6 +73,7 @@ namespace ICSharpCode.Decompiler.Tests.Helpers
 		CheckForOverflowUnderflow = 0x20000,
 		ProcessXmlDoc = 0x40000,
 		UseRoslyn4_14_0 = 0x80000,
+		EnableRuntimeAsync = 0x100000,
 		UseMcsMask = UseMcs2_6_4 | UseMcs5_23,
 		UseRoslynMask = UseRoslyn1_3_2 | UseRoslyn2_10_0 | UseRoslyn3_11_0 | UseRoslyn4_14_0 | UseRoslynLatest
 	}
@@ -500,6 +501,10 @@ namespace System.Runtime.CompilerServices
 				preprocessorSymbols.Add("LEGACY_CSC");
 				preprocessorSymbols.Add("LEGACY_VBC");
 			}
+			if (flags.HasFlag(CompilerOptions.EnableRuntimeAsync))
+			{
+				preprocessorSymbols.Add("RUNTIMEASYNC");
+			}
 			return preprocessorSymbols;
 		}
 
@@ -605,13 +610,18 @@ namespace System.Runtime.CompilerServices
 				if (roslynVersion != "legacy")
 				{
 					otherOptions += "/shared ";
-					if (!targetNet40 && Version.Parse(RoslynToolset.SanitizeVersion(roslynVersion)).Major > 2)
+					var version = Version.Parse(RoslynToolset.SanitizeVersion(roslynVersion));
+					if (!targetNet40 && version.Major > 2)
 					{
 						if (flags.HasFlag(CompilerOptions.NullableEnable))
 							otherOptions += "/nullable+ ";
 						else
 							otherOptions += "/nullable- ";
 					}
+					if (!targetNet40 && roslynVersion == roslynLatestVersion && flags.HasFlag(CompilerOptions.EnableRuntimeAsync))
+					{
+						otherOptions += "/features:runtime-async=on ";
+					}
 				}
 
 				if (flags.HasFlag(CompilerOptions.Library))
@@ -842,6 +852,8 @@ namespace System.Runtime.CompilerServices
 				suffix += ".mcs2";
 			if ((cscOptions & CompilerOptions.UseMcs5_23) != 0)
 				suffix += ".mcs5";
+			if ((cscOptions & CompilerOptions.EnableRuntimeAsync) != 0)
+				suffix += ".runtimeasync";
 			return suffix;
 		}
 

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -537,6 +537,46 @@ namespace ICSharpCode.Decompiler.Tests
 			await RunForLibrary(cscOptions: cscOptions);
 		}
 
+		[Test]
+		public async Task RuntimeAsync([ValueSource(nameof(roslyn5OrNewerOptions))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary("Async", cscOptions: cscOptions | CompilerOptions.EnableRuntimeAsync | CompilerOptions.Preview);
+		}
+
+		[Test]
+		public async Task RuntimeAsyncForeach([ValueSource(nameof(roslyn5OrNewerOptions))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary("AsyncForeach", cscOptions: cscOptions | CompilerOptions.EnableRuntimeAsync | CompilerOptions.Preview | CompilerOptions.GeneratePdb);
+		}
+
+		[Test]
+		public async Task RuntimeAsyncMain([ValueSource(nameof(roslyn5OrNewerOptions))] CompilerOptions cscOptions)
+		{
+			await Run("AsyncMain", cscOptions: cscOptions | CompilerOptions.EnableRuntimeAsync | CompilerOptions.Preview);
+		}
+
+		[Test]
+		public async Task RuntimeAsyncStreams([ValueSource(nameof(roslyn5OrNewerOptions))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary("AsyncStreams", cscOptions: cscOptions | CompilerOptions.EnableRuntimeAsync | CompilerOptions.Preview);
+		}
+
+		[Test]
+		public async Task RuntimeAsyncUsing([ValueSource(nameof(roslyn5OrNewerOptions))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary(
+				"AsyncUsing",
+				cscOptions: cscOptions | CompilerOptions.EnableRuntimeAsync | CompilerOptions.Preview,
+				configureDecompiler: settings => { settings.UseEnhancedUsing = false; }
+			);
+		}
+
+		[Test]
+		public async Task RuntimeAsyncCustomTaskType([ValueSource(nameof(roslyn5OrNewerOptions))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary("CustomTaskType", cscOptions: cscOptions | CompilerOptions.EnableRuntimeAsync | CompilerOptions.Preview);
+		}
+
 		[Test]
 		public async Task NullableRefTypes([ValueSource(nameof(roslyn3OrNewerOptions))] CompilerOptions cscOptions)
 		{

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

@@ -74,6 +74,12 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			Console.WriteLine("After");
 		}
 
+		[MethodImpl(MethodImplOptions.NoInlining)]
+		public async Task NoInliningTaskMethod()
+		{
+			await Task.Yield();
+		}
+
 		public async Task TaskMethodWithoutAwait()
 		{
 			Console.WriteLine("No Await");
@@ -115,6 +121,24 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 		}
 
+		public async Task AwaitConfigureAwaitFalse(Task<int> task)
+		{
+#if ROSLYN2
+			Console.WriteLine(await task.ConfigureAwait(continueOnCapturedContext: false));
+#else
+			Console.WriteLine(await task.ConfigureAwait(false));
+#endif
+		}
+
+		public async Task<int> AwaitConfigureAwaitMixed(Task<int> task1, Task<int> task2)
+		{
+#if ROSLYN2
+			return await task1.ConfigureAwait(continueOnCapturedContext: false) + await task2.ConfigureAwait(continueOnCapturedContext: true);
+#else
+			return await task1.ConfigureAwait(false) + await task2.ConfigureAwait(true);
+#endif
+		}
+
 #if CS60
 		public async Task AwaitInCatch(bool b, Task<int> task1, Task<int> task2)
 		{
@@ -359,6 +383,127 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 			return new object();
 		}
+
+		public async Task TryCatchFinallyAllAwait()
+		{
+			try
+			{
+				await Task.CompletedTask;
+				Console.WriteLine("try");
+			}
+			catch (Exception)
+			{
+				await Task.CompletedTask;
+				Console.WriteLine("catch");
+			}
+			finally
+			{
+				await Task.CompletedTask;
+				Console.WriteLine("finally");
+			}
+		}
+
+		public async Task ThrowInsideTryFinally()
+		{
+			try
+			{
+				throw new InvalidOperationException();
+			}
+			finally
+			{
+				await Task.Yield();
+			}
+		}
+
+		public async Task HeterogeneousMultiCatch1()
+		{
+			try
+			{
+				await Task.Yield();
+			}
+			catch (InvalidOperationException ex)
+			{
+				await Task.Yield();
+				Console.WriteLine(ex.Message);
+			}
+			catch (ArgumentException ex2)
+			{
+				await Task.Yield();
+				Console.WriteLine(ex2.Message);
+			}
+		}
+
+		public async Task HeterogeneousMultiCatch2()
+		{
+			try
+			{
+				await Task.Yield();
+			}
+			catch (InvalidOperationException ex)
+			{
+				await Task.Yield();
+				Console.WriteLine(ex.Message);
+			}
+			catch
+			{
+				await Task.Yield();
+				Console.WriteLine("other");
+			}
+		}
+
+		public async Task HeterogeneousMultiCatch3()
+		{
+			try
+			{
+				await Task.Yield();
+			}
+			catch (InvalidOperationException ex)
+			{
+				await Task.Yield();
+				Console.WriteLine(ex.Message);
+			}
+			catch (Exception)
+			{
+				await Task.Yield();
+				throw;
+			}
+		}
+#if RUNTIMEASYNC
+		// The state-machine async lowering doesn't recognize return-from-try-with-await-in-finally
+		// and decompiles these as `int result; try { ... } finally { ... } return result;`. The
+		// runtime-async exception rewrite recovers the source-level form. Gate these tests so the
+		// (state-machine) Async test doesn't run them against the more aggressive output.
+		public async Task<int> ReturnFromTryFinally()
+		{
+			try
+			{
+				return 42;
+			}
+			finally
+			{
+				await Task.CompletedTask;
+			}
+		}
+
+		public async Task<int> ReturnFromInsideNestedTryFinally()
+		{
+			try
+			{
+				try
+				{
+					return 42;
+				}
+				finally
+				{
+					await Task.CompletedTask;
+				}
+			}
+			finally
+			{
+				await Task.CompletedTask;
+			}
+		}
+#endif
 #endif
 
 		public static async Task<int> GetIntegerSumAsync(IEnumerable<int> items)

ICSharpCode.Decompiler/CSharp/CSharpLanguageVersion.cs

@@ -37,7 +37,8 @@ namespace ICSharpCode.Decompiler.CSharp
 		CSharp12_0 = 1200,
 		CSharp13_0 = 1300,
 		CSharp14_0 = 1400,
-		Preview = 1400,
+		CSharp15_0 = 1500,
+		Preview = 1500,
 		Latest = 0x7FFFFFFF
 	}
 }

ICSharpCode.Decompiler/DecompilerSettings.cs

@@ -177,10 +177,16 @@ namespace ICSharpCode.Decompiler
 				extensionMembers = false;
 				firstClassSpanTypes = false;
 			}
+			if (languageVersion < CSharp.LanguageVersion.CSharp15_0)
+			{
+				runtimeAsync = false;
+			}
 		}
 
 		public CSharp.LanguageVersion GetMinimumRequiredVersion()
 		{
+			if (runtimeAsync)
+				return CSharp.LanguageVersion.CSharp15_0;
 			if (extensionMembers || firstClassSpanTypes)
 				return CSharp.LanguageVersion.CSharp14_0;
 			if (paramsCollections)
@@ -2167,7 +2173,7 @@ namespace ICSharpCode.Decompiler
 		/// <summary>
 		/// Gets/Sets whether C# 14.0 extension members should be transformed.
 		/// </summary>
-		[Category("C# 14.0 / VS 202x.yy")]
+		[Category("C# 14.0 / VS 2026")]
 		[Description("DecompilerSettings.ExtensionMembers")]
 		public bool ExtensionMembers {
 			get { return extensionMembers; }
@@ -2185,7 +2191,7 @@ namespace ICSharpCode.Decompiler
 		/// <summary>
 		/// Gets/Sets whether (ReadOnly)Span&lt;T&gt; should be treated like built-in types.
 		/// </summary>
-		[Category("C# 14.0 / VS 202x.yy")]
+		[Category("C# 14.0 / VS 2026")]
 		[Description("DecompilerSettings.FirstClassSpanTypes")]
 		public bool FirstClassSpanTypes {
 			get { return firstClassSpanTypes; }
@@ -2198,6 +2204,24 @@ namespace ICSharpCode.Decompiler
 			}
 		}
 
+		bool runtimeAsync = true;
+
+		/// <summary>
+		/// Gets/Sets whether runtime async should be used.
+		/// </summary>
+		[Category("C# 15.0 / VS 202x.yy")]
+		[Description("DecompilerSettings.RuntimeAsync")]
+		public bool RuntimeAsync {
+			get { return runtimeAsync; }
+			set {
+				if (runtimeAsync != value)
+				{
+					runtimeAsync = value;
+					OnPropertyChanged();
+				}
+			}
+		}
+
 		bool separateLocalVariableDeclarations = false;
 
 		/// <summary>

ICSharpCode.Decompiler/ICSharpCode.Decompiler.csproj

@@ -149,6 +149,8 @@
     <Compile Include="Disassembler\DisassemblerSignatureTypeProvider.cs" />
     <Compile Include="Documentation\XmlDocumentationElement.cs" />
     <Compile Include="IL\ControlFlow\AwaitInFinallyTransform.cs" />
+    <Compile Include="IL\ControlFlow\RuntimeAsyncExceptionRewriteTransform.cs" />
+    <Compile Include="IL\ControlFlow\RuntimeAsyncManualAwaitTransform.cs" />
     <Compile Include="IL\Transforms\InterpolatedStringTransform.cs" />
     <Compile Include="IL\Transforms\IntroduceNativeIntTypeOnLocals.cs" />
     <Compile Include="IL\Transforms\LdLocaDupInitObjTransform.cs" />

ICSharpCode.Decompiler/IL/ControlFlow/AsyncAwaitDecompiler.cs

@@ -121,7 +121,15 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			awaitDebugInfos.Clear();
 			moveNextLeaves.Clear();
 			if (!MatchTaskCreationPattern(function) && !MatchAsyncEnumeratorCreationPattern(function))
+			{
+				if (function.IsAsync && context.Settings.RuntimeAsync)
+				{
+					TranslateThisCopyAccess(function);
+					RuntimeAsyncManualAwaitTransform.Run(function, context);
+					RuntimeAsyncExceptionRewriteTransform.Run(function, context);
+				}
 				return;
+			}
 			try
 			{
 				AnalyzeMoveNext();
@@ -174,6 +182,57 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			function.AsyncDebugInfo = new AsyncDebugInfo(catchHandlerOffset, awaitDebugInfos.ToImmutableArray());
 		}
 
+		// Runtime-async analog of fieldToParameterMap's `<>4__this` capture: in a struct method,
+		// Roslyn lowers `this` references to a single ldobj at function entry stored into a local.
+		// Match the entry instruction `stloc V_X(ldobj T(ldloc this))` and rewrite every later
+		// `ldloc V_X` / `ldloca V_X` to go through the `this` parameter again, so AST emission
+		// renders accesses as plain `this.field` / `field` rather than `<copy>.field`.
+		static bool TranslateThisCopyAccess(ILFunction function)
+		{
+			// Only applies to struct methods — that's the only shape where Roslyn copies *this
+			// at entry to keep the managed ref off the async resume path.
+			if (function.Method?.DeclaringTypeDefinition?.Kind != TypeKind.Struct)
+				return false;
+			var thisParam = function.Variables.FirstOrDefault(v => v.Kind == VariableKind.Parameter && v.Index == -1);
+			if (thisParam == null)
+				return false;
+			if (thisParam.Type is not ByReferenceType thisRef)
+				return false;
+			if (function.Body is not BlockContainer body || body.Blocks.Count == 0)
+				return false;
+			var entry = body.EntryPoint;
+			if (entry.Instructions.Count == 0)
+				return false;
+			if (!entry.Instructions[0].MatchStLoc(out var copyVar, out var copyValue))
+				return false;
+			if (copyVar.Kind != VariableKind.Local)
+				return false;
+			if (copyVar.StoreInstructions.Count != 1)
+				return false;
+			if (copyValue is not LdObj ldobj)
+				return false;
+			if (!ldobj.Target.MatchLdLoc(thisParam))
+				return false;
+			if (!copyVar.Type.Equals(ldobj.Type) || !thisRef.ElementType.Equals(ldobj.Type))
+				return false;
+
+			foreach (var ldloc in function.Descendants.OfType<LdLoc>().ToArray())
+			{
+				if (ldloc.Variable != copyVar)
+					continue;
+				ldloc.ReplaceWith(new LdObj(new LdLoc(thisParam), ldobj.Type).WithILRange(ldloc));
+			}
+			foreach (var ldloca in function.Descendants.OfType<LdLoca>().ToArray())
+			{
+				if (ldloca.Variable != copyVar)
+					continue;
+				ldloca.ReplaceWith(new LdLoc(thisParam).WithILRange(ldloca));
+			}
+
+			entry.Instructions.RemoveAt(0);
+			return true;
+		}
+
 		private void CleanUpBodyOfMoveNext(ILFunction function)
 		{
 			context.StepStartGroup("CleanUpBodyOfMoveNext", function);

ICSharpCode.Decompiler/IL/ControlFlow/AwaitInFinallyTransform.cs

@@ -78,31 +78,11 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				// [stloc V_3(ldloc E_100)	- copy exception variable to a temporary]
 				// stloc V_6(ldloc V_3)	- store exception in 'global' object variable
 				// br IL_0075				- jump out of catch block to the head of the finallyBlock
-				var catchBlockEntry = catchBlockContainer.EntryPoint;
-				ILVariable objectVariable;
-				switch (catchBlockEntry.Instructions.Count)
+				if (!MatchObjectStoreCatchHandler(catchBlockContainer, exceptionVariable,
+					out var objectVariable, out var entryPointOfFinally))
 				{
-					case 2:
-						if (!catchBlockEntry.Instructions[0].MatchStLoc(out objectVariable, out var value))
-							continue;
-						if (!value.MatchLdLoc(exceptionVariable))
-							continue;
-						break;
-					case 3:
-						if (!catchBlockEntry.Instructions[0].MatchStLoc(out var temporaryVariable, out value))
-							continue;
-						if (!value.MatchLdLoc(exceptionVariable))
-							continue;
-						if (!catchBlockEntry.Instructions[1].MatchStLoc(out objectVariable, out value))
-							continue;
-						if (!value.MatchLdLoc(temporaryVariable))
-							continue;
-						break;
-					default:
-						continue;
-				}
-				if (!catchBlockEntry.Instructions[catchBlockEntry.Instructions.Count - 1].MatchBranch(out var entryPointOfFinally))
 					continue;
+				}
 				// globalCopyVar should only be used once, at the end of the finally-block
 				if (objectVariable.LoadCount != 1 || objectVariable.StoreCount > 2)
 					continue;
@@ -136,7 +116,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				tryCatch.ReplaceWith(new TryFinally(tryCatch.TryBlock, finallyContainer).WithILRange(tryCatch.TryBlock));
 
 				context.Step("Move blocks into finally", finallyContainer);
-				MoveDominatedBlocksToContainer(entryPointOfFinally, beforeExceptionCaptureBlock, cfg, finallyContainer);
+				MoveDominatedBlocksToContainer(entryPointOfFinally, beforeExceptionCaptureBlock, cfg, finallyContainer, context);
 
 				SimplifyEndOfFinally(context, objectVariable, beforeExceptionCaptureBlock, objectVariableCopy, finallyContainer);
 
@@ -193,38 +173,6 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				}
 			}
 
-			void MoveDominatedBlocksToContainer(Block newEntryPoint, Block endBlock, ControlFlowGraph graph,
-				BlockContainer targetContainer)
-			{
-				var node = graph.GetNode(newEntryPoint);
-				var endNode = endBlock == null ? null : graph.GetNode(endBlock);
-
-				MoveBlock(newEntryPoint, targetContainer);
-
-				foreach (var n in graph.cfg)
-				{
-					Block block = (Block)n.UserData;
-
-					if (node.Dominates(n))
-					{
-						if (endNode != null && endNode != n && endNode.Dominates(n))
-							continue;
-
-						if (block.Parent == targetContainer)
-							continue;
-
-						MoveBlock(block, targetContainer);
-					}
-				}
-			}
-
-			void MoveBlock(Block block, BlockContainer target)
-			{
-				context.Step($"Move {block.Label} to container at IL_{target.StartILOffset:x4}", target);
-				block.Remove();
-				target.Blocks.Add(block);
-			}
-
 			static void SimplifyEndOfFinally(ILTransformContext context, ILVariable objectVariable, Block beforeExceptionCaptureBlock, ILVariable objectVariableCopy, BlockContainer finallyContainer)
 			{
 				if (beforeExceptionCaptureBlock.Instructions.Count >= 3
@@ -281,6 +229,82 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			return true;
 		}
 
+		/// <summary>
+		/// Matches a catch handler that stores its exception in an "object"-typed local and then
+		/// branches out of the catch:
+		///     [stloc tmp(ldloc exceptionVariable);]
+		///     stloc objectVariable(ldloc tmp_or_exceptionVariable)
+		///     br branchTarget
+		/// Used by the state-machine async lowering AND by the runtime-async try-finally lowering.
+		/// </summary>
+		internal static bool MatchObjectStoreCatchHandler(BlockContainer catchBlockContainer,
+			ILVariable exceptionVariable, out ILVariable objectVariable, out Block branchTarget)
+		{
+			objectVariable = null;
+			branchTarget = null;
+			var entry = catchBlockContainer.EntryPoint;
+			ILInstruction value;
+			switch (entry.Instructions.Count)
+			{
+				case 2:
+					if (!entry.Instructions[0].MatchStLoc(out objectVariable, out value))
+						return false;
+					if (!value.MatchLdLoc(exceptionVariable))
+						return false;
+					break;
+				case 3:
+					if (!entry.Instructions[0].MatchStLoc(out var temporaryVariable, out value))
+						return false;
+					if (!value.MatchLdLoc(exceptionVariable))
+						return false;
+					if (!entry.Instructions[1].MatchStLoc(out objectVariable, out value))
+						return false;
+					if (!value.MatchLdLoc(temporaryVariable))
+						return false;
+					break;
+				default:
+					return false;
+			}
+			return entry.Instructions[entry.Instructions.Count - 1].MatchBranch(out branchTarget);
+		}
+
+		/// <summary>
+		/// Move <paramref name="newEntryPoint"/> and every block it dominates (excluding any block
+		/// dominated by <paramref name="endBlock"/> other than <paramref name="endBlock"/> itself)
+		/// from their current container into <paramref name="targetContainer"/>.
+		/// </summary>
+		internal static void MoveDominatedBlocksToContainer(Block newEntryPoint, Block endBlock,
+			ControlFlowGraph graph, BlockContainer targetContainer, ILTransformContext context)
+		{
+			var node = graph.GetNode(newEntryPoint);
+			var endNode = endBlock == null ? null : graph.GetNode(endBlock);
+
+			MoveBlock(newEntryPoint, targetContainer, context);
+
+			foreach (var n in graph.cfg)
+			{
+				Block block = (Block)n.UserData;
+
+				if (node.Dominates(n))
+				{
+					if (endNode != null && endNode != n && endNode.Dominates(n))
+						continue;
+
+					if (block.Parent == targetContainer)
+						continue;
+
+					MoveBlock(block, targetContainer, context);
+				}
+			}
+		}
+
+		static void MoveBlock(Block block, BlockContainer target, ILTransformContext context)
+		{
+			context.Step($"Move {block.Label} to container at IL_{target.StartILOffset:x4}", target);
+			block.Remove();
+			target.Blocks.Add(block);
+		}
+
 		static (Block, Block, ILVariable) FindBlockAfterFinally(ILTransformContext context, Block block, ILVariable objectVariable)
 		{
 			// Block IL_0327 (incoming: 2) {

ICSharpCode.Decompiler/IL/ControlFlow/RuntimeAsyncManualAwaitTransform.cs

@@ -0,0 +1,177 @@
+// Copyright (c) 2026 Siegfried Pammer
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using System.Linq;
+
+using ICSharpCode.Decompiler.IL.Transforms;
+
+namespace ICSharpCode.Decompiler.IL.ControlFlow
+{
+	/// <summary>
+	/// Collapses the runtime-async manual await pattern (GetAwaiter / get_IsCompleted /
+	/// AsyncHelpers.UnsafeAwaitAwaiter / GetResult across three blocks) into a single IL
+	/// Await instruction, matching what the state-machine async pipeline emits.
+	/// </summary>
+	static class RuntimeAsyncManualAwaitTransform
+	{
+		public static void Run(ILFunction function, ILTransformContext context)
+		{
+			bool changed = false;
+			foreach (var block in function.Descendants.OfType<Block>().ToArray())
+			{
+				if (DetectRuntimeAsyncManualAwait(block, context))
+					changed = true;
+			}
+			if (changed)
+			{
+				foreach (var c in function.Body.Descendants.OfType<BlockContainer>())
+					c.SortBlocks(deleteUnreachableBlocks: true);
+			}
+		}
+
+		// Block X (head) {
+		//     [stloc awaitable(<value>);]                       (optional: when GetAwaiter takes an address)
+		//     stloc awaiter(call GetAwaiter(<expr>))
+		//     if (call get_IsCompleted(ldloca awaiter)) br completedBlock
+		//     br pauseBlock
+		// }
+		// Block pauseBlock {
+		//     call AsyncHelpers.UnsafeAwaitAwaiter[<T>](ldloc awaiter)
+		//     br completedBlock
+		// }
+		// Block completedBlock {
+		//     call GetResult(ldloca awaiter)                     (possibly inlined into a containing expression)
+		//     ...
+		// }
+		// =>
+		// Block X { ...; br completedBlock }
+		// Block completedBlock { <Await(value)>; ... }
+		static bool DetectRuntimeAsyncManualAwait(Block block, ILTransformContext context)
+		{
+			if (block.Instructions.Count < 3)
+				return false;
+
+			if (!block.Instructions[^3].MatchStLoc(out var awaiterVar, out var awaiterValue))
+				return false;
+			if (awaiterValue is not CallInstruction getAwaiterCall)
+				return false;
+			if (getAwaiterCall.Method.Name != "GetAwaiter" || getAwaiterCall.Arguments.Count != 1)
+				return false;
+
+			if (block.Instructions[^2] is not IfInstruction ifInst)
+				return false;
+			var condition = ifInst.Condition;
+			if (condition.MatchLogicNot(out var negated))
+				condition = negated;
+			if (condition is not CallInstruction isCompletedCall)
+				return false;
+			if (isCompletedCall.Method.Name != "get_IsCompleted" || isCompletedCall.Arguments.Count != 1)
+				return false;
+			if (!isCompletedCall.Arguments[0].MatchLdLoca(awaiterVar))
+				return false;
+
+			Block completedBlock, pauseBlock;
+			if (ifInst.TrueInst.MatchBranch(out var trueBranchTarget) && block.Instructions[^1].MatchBranch(out var falseBranchTarget))
+			{
+				if (negated != null)
+				{
+					// if (!IsCompleted) br pauseBlock; br completedBlock — flipped
+					pauseBlock = trueBranchTarget;
+					completedBlock = falseBranchTarget;
+				}
+				else
+				{
+					// if (IsCompleted) br completedBlock; br pauseBlock — canonical
+					completedBlock = trueBranchTarget;
+					pauseBlock = falseBranchTarget;
+				}
+			}
+			else
+			{
+				return false;
+			}
+
+			// Block pauseBlock { call AsyncHelpers.UnsafeAwaitAwaiter(ldloc awaiter); br completedBlock }
+			if (pauseBlock.Instructions.Count != 2)
+				return false;
+			if (pauseBlock.Instructions[0] is not Call pauseCall)
+				return false;
+			if (!EarlyExpressionTransforms.IsAsyncHelpersMethod(pauseCall.Method, "UnsafeAwaitAwaiter") || pauseCall.Arguments.Count != 1)
+				return false;
+			if (!pauseCall.Arguments[0].MatchLdLoc(awaiterVar))
+				return false;
+			if (!pauseBlock.Instructions[1].MatchBranch(out var pauseTail) || pauseTail != completedBlock)
+				return false;
+
+			// completedBlock starts with: GetResult(ldloca awaiter), possibly inlined.
+			if (completedBlock.Instructions.Count < 1)
+				return false;
+			var getResultCall = ILInlining.FindFirstInlinedCall(completedBlock.Instructions[0]);
+			if (getResultCall == null)
+				return false;
+			if (getResultCall.Method.Name != "GetResult" || getResultCall.Arguments.Count != 1)
+				return false;
+			if (!getResultCall.Arguments[0].MatchLdLoca(awaiterVar))
+				return false;
+
+			// Determine the awaitable expression: the original GetAwaiter argument (often `ldloca tmp`)
+			// or, if `tmp` is a fresh temporary set immediately above, the value it was set to.
+			ILInstruction awaitable;
+			bool removeTemporaryStore = false;
+			if (getAwaiterCall.Arguments[0].MatchLdLoca(out var tmpVar)
+				&& block.Instructions.Count >= 4
+				&& block.Instructions[^4].MatchStLoc(tmpVar, out var tmpValue)
+				&& tmpVar.StoreCount == 1
+				&& tmpVar.LoadCount == 0
+				&& tmpVar.AddressCount == 1)
+			{
+				awaitable = tmpValue;
+				removeTemporaryStore = true;
+			}
+			else
+			{
+				awaitable = getAwaiterCall.Arguments[0];
+			}
+
+			context.Step("Reduce manual await pattern to Await", block);
+
+			// Capture IL ranges before we remove the suspend machinery. The new Await stands in
+			// for the whole pattern (temp store + GetAwaiter + IsCompleted check + UnsafeAwaitAwaiter
+			// + GetResult), and the new `br completedBlock` replaces the original `br pauseBlock`.
+			var oldTailBranch = block.Instructions[^1];
+			var awaitInst = new Await(awaitable.Clone()).WithILRange(getResultCall);
+			if (removeTemporaryStore)
+				awaitInst.AddILRange(block.Instructions[^4]);
+			awaitInst.AddILRange(block.Instructions[^3]);
+			awaitInst.AddILRange(block.Instructions[^2]);
+			foreach (var inst in pauseBlock.Instructions)
+				awaitInst.AddILRange(inst);
+			awaitInst.GetAwaiterMethod = getAwaiterCall.Method;
+			awaitInst.GetResultMethod = getResultCall.Method;
+
+			// Remove the trailing 3 (or 4) instructions of the head block; replace with `br completedBlock`.
+			int removeCount = removeTemporaryStore ? 4 : 3;
+			block.Instructions.RemoveRange(block.Instructions.Count - removeCount, removeCount);
+			block.Instructions.Add(new Branch(completedBlock).WithILRange(oldTailBranch));
+
+			getResultCall.ReplaceWith(awaitInst);
+
+			return true;
+		}
+	}
+}

ICSharpCode.Decompiler/IL/ILReader.cs

@@ -159,6 +159,7 @@ namespace ICSharpCode.Decompiler.IL
 		BitSet isBranchTarget = null!;
 		BlockContainer mainContainer = null!;
 		int currentInstructionStart;
+		bool isRuntimeAsync;
 
 		Dictionary<int, ImportedBlock> blocksByOffset = new Dictionary<int, ImportedBlock>();
 		Queue<ImportedBlock> importQueue = new Queue<ImportedBlock>();
@@ -172,6 +173,8 @@ namespace ICSharpCode.Decompiler.IL
 			if (methodDefinitionHandle.IsNil)
 				throw new ArgumentException("methodDefinitionHandle.IsNil");
 			this.method = module.GetDefinition(methodDefinitionHandle);
+			this.isRuntimeAsync = (module.TypeSystemOptions & TypeSystemOptions.RuntimeAsync) != 0
+				&& (module.metadata.GetMethodDefinition(methodDefinitionHandle).ImplAttributes & SRMExtensions.MethodImplAsync) != 0;
 			if (genericContext.ClassTypeParameters == null && genericContext.MethodTypeParameters == null)
 			{
 				// no generic context specified: use the method's own type parameters
@@ -187,7 +190,14 @@ namespace ICSharpCode.Decompiler.IL
 			this.reader = body.GetILReader();
 			this.currentStack = ImmutableStack<ILVariable>.Empty;
 			this.expressionStack.Clear();
-			this.methodReturnStackType = method.ReturnType.GetStackType();
+			if (isRuntimeAsync)
+			{
+				this.methodReturnStackType = TaskType.UnpackAnyTask(compilation, method.ReturnType).GetStackType();
+			}
+			else
+			{
+				this.methodReturnStackType = method.ReturnType.GetStackType();
+			}
 			InitParameterVariables();
 			localVariables = InitLocalVariables();
 			foreach (var v in localVariables)
@@ -715,6 +725,10 @@ namespace ICSharpCode.Decompiler.IL
 			var blockBuilder = new BlockBuilder(body, variableByExceptionHandler, compilation);
 			blockBuilder.CreateBlocks(mainContainer, blocksByOffset.Values.Select(ib => ib.Block), cancellationToken);
 			var function = new ILFunction(this.method, body.GetCodeSize(), this.genericContext, mainContainer, kind);
+			if (isRuntimeAsync)
+			{
+				function.AsyncReturnType = TaskType.UnpackAnyTask(compilation, this.method.ReturnType);
+			}
 			function.Variables.AddRange(parameterVariables);
 			function.Variables.AddRange(localVariables);
 			function.LocalVariableSignatureLength = localVariables.Length;

ICSharpCode.Decompiler/IL/Transforms/EarlyExpressionTransforms.cs

@@ -173,6 +173,39 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 		}
 
+		protected internal override void VisitCall(Call inst)
+		{
+			base.VisitCall(inst);
+			TransformAsyncHelpersAwaitToAwait(inst, context);
+		}
+
+		// runtime-async lowering emits `call AsyncHelpers.Await(value)` in place of the IL Await
+		// instruction. Convert it back so downstream transforms (UsingTransform's MatchDisposeBlock
+		// and friends pattern-match on Await via UnwrapAwait) see the canonical shape that the
+		// state-machine async pipeline also produces. Gate on the current function actually being
+		// a runtime-async method — ILReader sets IsAsync iff the MethodImpl.Async bit is present —
+		// so a non-async method that calls the helper directly (legal, just unusual) doesn't get
+		// rewritten into IL that the surrounding non-async control flow can't represent.
+		internal static bool TransformAsyncHelpersAwaitToAwait(Call inst, ILTransformContext context)
+		{
+			if (!context.Settings.RuntimeAsync || !context.Function.IsAsync)
+				return false;
+			if (!inst.Method.IsStatic || inst.Arguments.Count != 1 || !IsAsyncHelpersMethod(inst.Method, "Await"))
+				return false;
+			context.Step("call AsyncHelpers.Await(value) => await(value)", inst);
+			var awaitInst = new Await(inst.Arguments[0]).WithILRange(inst);
+			awaitInst.GetAwaiterMethod = null;
+			awaitInst.GetResultMethod = inst.Method;
+			inst.ReplaceWith(awaitInst);
+			return true;
+		}
+
+		internal static bool IsAsyncHelpersMethod(IMethod method, string name)
+		{
+			return method.Name == name
+				&& method.DeclaringType?.FullName == "System.Runtime.CompilerServices.AsyncHelpers";
+		}
+
 		protected internal override void VisitNewObj(NewObj inst)
 		{
 			if (TransformDecimalCtorToConstant(inst, out LdcDecimal decimalConstant))

ICSharpCode.Decompiler/SRMHacks.cs

@@ -15,6 +15,7 @@ namespace ICSharpCode.Decompiler
 	public static partial class SRMExtensions
 	{
 		internal const GenericParameterAttributes AllowByRefLike = (GenericParameterAttributes)0x0020;
+		internal const MethodImplAttributes MethodImplAsync = (MethodImplAttributes)0x2000;
 
 		public static ImmutableArray<MethodImplementationHandle> GetMethodImplementations(
 			this MethodDefinitionHandle handle, MetadataReader reader)

ICSharpCode.Decompiler/TypeSystem/DecompilerTypeSystem.cs

@@ -154,12 +154,17 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// </summary>
 		ExtensionMembers = 0x80000,
 		/// <summary>
+		/// If this option is active, methods with the MethodImplAttribute(MethodImplOptions.Async) are treated as async methods.
+		/// </summary>
+		RuntimeAsync = 0x100000,
+		/// <summary>
 		/// Default settings: typical options for the decompiler, with all C# language features enabled.
 		/// </summary>
 		Default = Dynamic | Tuple | ExtensionMethods | DecimalConstants | ReadOnlyStructsAndParameters
 			| RefStructs | UnmanagedConstraints | NullabilityAnnotations | ReadOnlyMethods
 			| NativeIntegers | FunctionPointers | ScopedRef | NativeIntegersWithoutAttribute
 			| RefReadOnlyParameters | ParamsCollections | FirstClassSpanTypes | ExtensionMembers
+			| RuntimeAsync
 	}
 
 	/// <summary>
@@ -207,6 +212,8 @@ namespace ICSharpCode.Decompiler.TypeSystem
 				typeSystemOptions |= TypeSystemOptions.FirstClassSpanTypes;
 			if (settings.ExtensionMembers)
 				typeSystemOptions |= TypeSystemOptions.ExtensionMembers;
+			if (settings.RuntimeAsync)
+				typeSystemOptions |= TypeSystemOptions.RuntimeAsync;
 			return typeSystemOptions;
 		}
 

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataMethod.cs

@@ -350,6 +350,10 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			var metadata = module.metadata;
 			var def = metadata.GetMethodDefinition(handle);
 			MethodImplAttributes implAttributes = def.ImplAttributes & ~MethodImplAttributes.CodeTypeMask;
+			if ((module.TypeSystemOptions & TypeSystemOptions.RuntimeAsync) != 0)
+			{
+				implAttributes &= ~SRMExtensions.MethodImplAsync;
+			}
 			int methodCodeType = (int)(def.ImplAttributes & MethodImplAttributes.CodeTypeMask);
 
 			#region DllImportAttribute

ICSharpCode.Decompiler/TypeSystem/TaskType.cs

@@ -40,6 +40,28 @@ namespace ICSharpCode.Decompiler.TypeSystem
 				return type.TypeArguments[0];
 		}
 
+		/// <summary>
+		/// Gets the element type of any task-like type (Task, Task&lt;T&gt;, ValueTask,
+		/// ValueTask&lt;T&gt;, or any [AsyncMethodBuilder]-attributed custom task type).
+		/// Returns void for non-generic task-likes. Any other type is returned unmodified.
+		/// </summary>
+		public static IType UnpackAnyTask(ICompilation compilation, IType type)
+		{
+			if (IsTask(type))
+			{
+				return type.TypeParameterCount == 0
+					? compilation.FindType(KnownTypeCode.Void)
+					: type.TypeArguments[0];
+			}
+			if (IsCustomTask(type, out _))
+			{
+				return type.TypeParameterCount == 0
+					? compilation.FindType(KnownTypeCode.Void)
+					: type.TypeArguments[0];
+			}
+			return type;
+		}
+
 		/// <summary>
 		/// Gets whether the specified type is Task or Task&lt;T&gt;.
 		/// </summary>

ILSpy/Languages/CSharpLanguage.cs

@@ -24,8 +24,6 @@ using System.Linq;
 using System.Reflection;
 using System.Reflection.Metadata;
 using System.Reflection.PortableExecutable;
-using System.Windows;
-using System.Windows.Controls;
 
 using ICSharpCode.AvalonEdit.Highlighting;
 using ICSharpCode.Decompiler;
@@ -119,6 +117,7 @@ namespace ICSharpCode.ILSpy
 						new LanguageVersion(Decompiler.CSharp.LanguageVersion.CSharp12_0.ToString(), "C# 12.0 / VS 2022.8"),
 						new LanguageVersion(Decompiler.CSharp.LanguageVersion.CSharp13_0.ToString(), "C# 13.0 / VS 2022.12"),
 						new LanguageVersion(Decompiler.CSharp.LanguageVersion.CSharp14_0.ToString(), "C# 14.0 / VS 2026"),
+						new LanguageVersion(Decompiler.CSharp.LanguageVersion.CSharp15_0.ToString(), "C# 15.0 / VS 202x.yy"),
 					};
 				}
 				return versions;

ILSpy/Properties/Resources.Designer.cs

@@ -1360,7 +1360,16 @@ namespace ICSharpCode.ILSpy.Properties {
                 return ResourceManager.GetString("DecompilerSettings.RequiredMembers", resourceCulture);
             }
         }
-        
+
+        /// <summary>
+        ///   Looks up a localized string similar to Decompile runtime-async (System.Runtime.CompilerServices.AsyncHelpers) methods.
+        /// </summary>
+        public static string DecompilerSettings_RuntimeAsync {
+            get {
+                return ResourceManager.GetString("DecompilerSettings.RuntimeAsync", resourceCulture);
+            }
+        }
+
         /// <summary>
         ///   Looks up a localized string similar to &apos;scoped&apos; lifetime annotation.
         /// </summary>

ILSpy/Properties/Resources.resx

@@ -474,6 +474,9 @@ Are you sure you want to continue?</value>
   <data name="DecompilerSettings.RequiredMembers" xml:space="preserve">
     <value>Required members</value>
   </data>
+  <data name="DecompilerSettings.RuntimeAsync" xml:space="preserve">
+    <value>Decompile runtime-async (System.Runtime.CompilerServices.AsyncHelpers) methods</value>
+  </data>
   <data name="DecompilerSettings.ScopedRef" xml:space="preserve">
     <value>'scoped' lifetime annotation</value>
   </data>