Add support for C# 8.0 disposable ref structs

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

@@ -39,6 +39,25 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 		}
 
+#if CS80
+		[StructLayout(LayoutKind.Sequential, Size = 1)]
+		public ref struct UsingRefStruct
+		{
+			public int i;
+
+			public UsingRefStruct(int i)
+			{
+				this.i = i;
+				Console.WriteLine(i);
+			}
+
+			public void Dispose()
+			{
+				throw new NotImplementedException();
+			}
+		}
+#endif
+
 #if LEGACY_CSC
 		// roslyn optimizes out the try-finally; mcs has a compiler bug on using(null-literal)
 		public void SimpleUsingNullStatement()
@@ -121,5 +140,14 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 				Console.WriteLine(t);
 			}
 		}
+
+#if CS80
+		public void UsingRefStruct1(UsingRefStruct s)
+		{
+			using (s) {
+				Console.WriteLine(s.i);
+			}
+		}
+#endif
 	}
 }

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -426,7 +426,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				disposeType = exprBuilder.compilation.FindType(KnownTypeCode.IDisposable);
 				disposeTypeMethodName = "Dispose";
 			}
-			if (!inst.ResourceExpression.MatchLdNull() && !NullableType.GetUnderlyingType(var.Type).GetAllBaseTypes().Any(b => b.IsKnownType(knownTypeCode))) {
+			if (!IsValidInCSharp(inst, knownTypeCode)) {
 				Debug.Assert(var.Kind == VariableKind.UsingLocal);
 				var.Kind = VariableKind.Local;
 				var disposeVariable = currentFunction.RegisterVariable(
@@ -463,6 +463,15 @@ namespace ICSharpCode.Decompiler.CSharp
 					EmbeddedStatement = ConvertAsBlock(inst.Body)
 				}.WithILInstruction(inst);
 			}
+
+			bool IsValidInCSharp(UsingInstruction inst, KnownTypeCode code)
+			{
+				if (inst.ResourceExpression.MatchLdNull())
+					return true;
+				if (inst.IsRefStruct)
+					return true;
+				return NullableType.GetUnderlyingType(var.Type).GetAllBaseTypes().Any(b => b.IsKnownType(code));
+			}
 		}
 
 		Statement TransformToForeach(UsingInstruction inst, Expression resource)

ICSharpCode.Decompiler/IL/Instructions/UsingInstruction.cs

@@ -38,6 +38,8 @@ namespace ICSharpCode.Decompiler.IL
 	{
 		public bool IsAsync { get; set; }
 
+		public bool IsRefStruct { get; set; }
+
 		public override void WriteTo(ITextOutput output, ILAstWritingOptions options)
 		{
 			WriteILRange(output, options);
@@ -45,6 +47,9 @@ namespace ICSharpCode.Decompiler.IL
 			if (IsAsync) {
 				output.Write(".async");
 			}
+			if (IsRefStruct) {
+				output.Write(".ref");
+			}
 			output.Write(" (");
 			Variable.WriteTo(output);
 			output.Write(" = ");

ICSharpCode.Decompiler/IL/Transforms/UsingTransform.cs

@@ -89,7 +89,9 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			context.Step("UsingTransform", tryFinally);
 			storeInst.Variable.Kind = VariableKind.UsingLocal;
 			block.Instructions.RemoveAt(i);
-			block.Instructions[i - 1] = new UsingInstruction(storeInst.Variable, storeInst.Value, tryFinally.TryBlock).WithILRange(storeInst);
+			block.Instructions[i - 1] = new UsingInstruction(storeInst.Variable, storeInst.Value, tryFinally.TryBlock) {
+				IsRefStruct = context.Settings.IntroduceRefModifiersOnStructs && storeInst.Variable.Type.Kind == TypeKind.Struct && storeInst.Variable.Type.IsByRefLike
+			}.WithILRange(storeInst);
 			return true;
 		}
 
@@ -152,6 +154,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return true;
 			if (NullableType.GetUnderlyingType(type).GetAllBaseTypes().Any(b => b.IsKnownType(KnownTypeCode.IDisposable)))
 				return true;
+			if (context.Settings.IntroduceRefModifiersOnStructs && type.Kind == TypeKind.Struct && type.IsByRefLike)
+				return true;
 			// General GetEnumerator-pattern?
 			if (!type.GetMethods(m => m.Name == "GetEnumerator" && m.TypeParameters.Count == 0 && m.Parameters.Count == 0).Any(m => ImplementsForeachPattern(m.ReturnType)))
 				return false;
@@ -198,11 +202,11 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool MatchDisposeCheck(ILVariable objVar, ILInstruction checkInst, bool isReference, bool usingNull, out int numObjVarLoadsInCheck, in string disposeMethodFullName, KnownTypeCode disposeTypeCode)
+		bool MatchDisposeCheck(ILVariable objVar, ILInstruction checkInst, bool isReference, bool usingNull, out int numObjVarLoadsInCheck, string disposeMethodFullName, KnownTypeCode disposeTypeCode)
 		{
 			numObjVarLoadsInCheck = 2;
 			ILInstruction disposeInvocation;
-			CallVirt callVirt;
+			CallInstruction disposeCall;
 			if (objVar.Type.IsKnownType(KnownTypeCode.NullableOfT)) {
 				if (checkInst.MatchIfInstruction(out var condition, out var disposeInst)) {
 					if (!NullableLiftingTransform.MatchHasValueCall(condition, objVar))
@@ -219,16 +223,16 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					if (!UnwrapAwait(ref disposeInvocation))
 						return false;
 				}
-				callVirt = disposeInvocation as CallVirt;
-				if (callVirt == null)
+				disposeCall = disposeInvocation as CallVirt;
+				if (disposeCall == null)
 					return false;
-				if (callVirt.Method.FullName != disposeMethodFullName)
+				if (disposeCall.Method.FullName != disposeMethodFullName)
 					return false;
-				if (callVirt.Method.Parameters.Count > 0)
+				if (disposeCall.Method.Parameters.Count > 0)
 					return false;
-				if (callVirt.Arguments.Count != 1)
+				if (disposeCall.Arguments.Count != 1)
 					return false;
-				var firstArg = callVirt.Arguments.FirstOrDefault();
+				var firstArg = disposeCall.Arguments.FirstOrDefault();
 				if (!(firstArg.MatchUnboxAny(out var innerArg1, out var unboxType) && unboxType.IsKnownType(disposeTypeCode))) {
 					if (!firstArg.MatchAddressOf(out var innerArg2, out _))
 						return false;
@@ -251,7 +255,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					if (!(cv.Arguments.FirstOrDefault() is NullableUnwrap unwrap))
 						return false;
 					numObjVarLoadsInCheck = 1;
-					callVirt = cv;
+					disposeCall = cv;
 					target = unwrap.Argument;
 				} else if (isReference) {
 					// reference types have a null check.
@@ -273,7 +277,17 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						return false;
 					if (target.MatchBox(out var newTarget, out var type) && type.Equals(objVar.Type))
 						target = newTarget;
-					callVirt = cv;
+					disposeCall = cv;
+				} else if (objVar.Type.Kind == TypeKind.Struct && objVar.Type.IsByRefLike) {
+					if (!(checkInst is Call call && call.Method.DeclaringType == objVar.Type))
+						return false;
+					target = call.Arguments.FirstOrDefault();
+					if (target == null)
+						return false;
+					if (call.Method.Name != "Dispose")
+						return false;
+					disposeMethodFullName = call.Method.FullName;
+					disposeCall = call;
 				} else {
 					if (disposeTypeCode == KnownTypeCode.IAsyncDisposable) {
 						if (!UnwrapAwait(ref checkInst))
@@ -288,17 +302,17 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						boxedValue = type.IsReferenceType != true;
 						target = newTarget;
 					}
-					callVirt = cv;
+					disposeCall = cv;
 				}
-				if (callVirt.Method.FullName != disposeMethodFullName)
+				if (disposeCall.Method.FullName != disposeMethodFullName)
 					return false;
-				if (callVirt.Method.Parameters.Count > 0)
+				if (disposeCall.Method.Parameters.Count > 0)
 					return false;
-				if (callVirt.Arguments.Count != 1)
+				if (disposeCall.Arguments.Count != 1)
 					return false;
 				return target.MatchLdLocRef(objVar)
 					|| (boxedValue && target.MatchLdLoc(objVar))
-					|| (usingNull && callVirt.Arguments[0].MatchLdNull())
+					|| (usingNull && disposeCall.Arguments[0].MatchLdNull())
 					|| (isReference && checkInst is NullableRewrap
 						&& target.MatchIsInst(out var arg, out var type2)
 						&& arg.MatchLdLoc(objVar) && type2.IsKnownType(disposeTypeCode));