Fix #1882: Provide a setting to desugar X? into Nullable<X> for value types

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -401,12 +401,13 @@ namespace ICSharpCode.Decompiler.CSharp
 			return new DecompilerTypeSystem(file, resolver);
 		}
 
-		static TypeSystemAstBuilder CreateAstBuilder(ITypeResolveContext decompilationContext)
+		static TypeSystemAstBuilder CreateAstBuilder(DecompilerSettings settings)
 		{
 			var typeSystemAstBuilder = new TypeSystemAstBuilder();
 			typeSystemAstBuilder.ShowAttributes = true;
 			typeSystemAstBuilder.AlwaysUseShortTypeNames = true;
 			typeSystemAstBuilder.AddResolveResultAnnotations = true;
+			typeSystemAstBuilder.UseNullableSpecifierForValueTypes = settings.LiftNullables;
 			return typeSystemAstBuilder;
 		}
 
@@ -421,7 +422,7 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		void RunTransforms(AstNode rootNode, DecompileRun decompileRun, ITypeResolveContext decompilationContext)
 		{
-			var typeSystemAstBuilder = CreateAstBuilder(decompilationContext);
+			var typeSystemAstBuilder = CreateAstBuilder(decompileRun.Settings);
 			var context = new TransformContext(typeSystem, decompileRun, decompilationContext, typeSystemAstBuilder);
 			foreach (var transform in astTransforms) {
 				CancellationToken.ThrowIfCancellationRequested();
@@ -466,13 +467,13 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			try {
 				foreach (var a in typeSystem.MainModule.GetAssemblyAttributes()) {
-					var astBuilder = CreateAstBuilder(decompilationContext);
+					var astBuilder = CreateAstBuilder(decompileRun.Settings);
 					var attrSection = new AttributeSection(astBuilder.ConvertAttribute(a));
 					attrSection.AttributeTarget = "assembly";
 					syntaxTree.AddChild(attrSection, SyntaxTree.MemberRole);
 				}
 				foreach (var a in typeSystem.MainModule.GetModuleAttributes()) {
-					var astBuilder = CreateAstBuilder(decompilationContext);
+					var astBuilder = CreateAstBuilder(decompileRun.Settings);
 					var attrSection = new AttributeSection(astBuilder.ConvertAttribute(a));
 					attrSection.AttributeTarget = "module";
 					syntaxTree.AddChild(attrSection, SyntaxTree.MemberRole);
@@ -1076,7 +1077,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			Debug.Assert(decompilationContext.CurrentTypeDefinition == typeDef);
 			try {
-				var typeSystemAstBuilder = CreateAstBuilder(decompilationContext);
+				var typeSystemAstBuilder = CreateAstBuilder(decompileRun.Settings);
 				var entityDecl = typeSystemAstBuilder.ConvertEntity(typeDef);
 				var typeDecl = entityDecl as TypeDeclaration;
 				if (typeDecl == null) {
@@ -1239,7 +1240,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		EntityDeclaration DoDecompile(IMethod method, DecompileRun decompileRun, ITypeResolveContext decompilationContext)
 		{
 			Debug.Assert(decompilationContext.CurrentMember == method);
-			var typeSystemAstBuilder = CreateAstBuilder(decompilationContext);
+			var typeSystemAstBuilder = CreateAstBuilder(decompileRun.Settings);
 			var methodDecl = typeSystemAstBuilder.ConvertEntity(method);
 			int lastDot = method.Name.LastIndexOf('.');
 			if (method.IsExplicitInterfaceImplementation && lastDot >= 0) {
@@ -1412,7 +1413,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			Debug.Assert(decompilationContext.CurrentMember == field);
 			try {
-				var typeSystemAstBuilder = CreateAstBuilder(decompilationContext);
+				var typeSystemAstBuilder = CreateAstBuilder(decompileRun.Settings);
 				if (decompilationContext.CurrentTypeDefinition.Kind == TypeKind.Enum && field.IsConst) {
 					var enumDec = new EnumMemberDeclaration { Name = field.Name };
 					object constantValue = field.GetConstantValue();
@@ -1483,7 +1484,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			Debug.Assert(decompilationContext.CurrentMember == property);
 			try {
-				var typeSystemAstBuilder = CreateAstBuilder(decompilationContext);
+				var typeSystemAstBuilder = CreateAstBuilder(decompileRun.Settings);
 				EntityDeclaration propertyDecl = typeSystemAstBuilder.ConvertEntity(property);
 				if (property.IsExplicitInterfaceImplementation && !property.IsIndexer) {
 					int lastDot = property.Name.LastIndexOf('.');
@@ -1518,7 +1519,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			Debug.Assert(decompilationContext.CurrentMember == ev);
 			try {
-				var typeSystemAstBuilder = CreateAstBuilder(decompilationContext);
+				var typeSystemAstBuilder = CreateAstBuilder(decompileRun.Settings);
 				typeSystemAstBuilder.UseCustomEvents = ev.DeclaringTypeDefinition.Kind != TypeKind.Interface;
 				var eventDecl = typeSystemAstBuilder.ConvertEntity(ev);
 				int lastDot = ev.Name.LastIndexOf('.');

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -92,6 +92,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			this.astBuilder = new TypeSystemAstBuilder(resolver);
 			this.astBuilder.AlwaysUseShortTypeNames = true;
 			this.astBuilder.AddResolveResultAnnotations = true;
+			this.astBuilder.UseNullableSpecifierForValueTypes = settings.LiftNullables;
 			this.typeInference = new TypeInference(compilation) { Algorithm = TypeInferenceAlgorithm.Improved };
 		}
 

ICSharpCode.Decompiler/CSharp/OutputVisitor/CSharpAmbience.cs

@@ -195,6 +195,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			astBuilder.ShowAccessibility = (ConversionFlags & ConversionFlags.ShowAccessibility) == ConversionFlags.ShowAccessibility;
 			astBuilder.AlwaysUseShortTypeNames = (ConversionFlags & ConversionFlags.UseFullyQualifiedTypeNames) != ConversionFlags.UseFullyQualifiedTypeNames;
 			astBuilder.ShowParameterNames = (ConversionFlags & ConversionFlags.ShowParameterNames) == ConversionFlags.ShowParameterNames;
+			astBuilder.UseNullableSpecifierForValueTypes = (ConversionFlags & ConversionFlags.UseNullableSpecifierForValueTypes) != 0;
 			return astBuilder;
 		}
 

ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs

@@ -64,7 +64,8 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		#region Properties
 		void InitProperties()
 		{
-			this.AlwaysUseBuiltinTypeNames = true;
+			this.UseKeywordsForBuiltinTypes = true;
+			this.UseNullableSpecifierForValueTypes = true;
 			this.ShowAccessibility = true;
 			this.ShowModifiers = true;
 			this.ShowBaseTypes = true;
@@ -78,82 +79,88 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		
 		/// <summary>
 		/// Specifies whether the ast builder should add annotations to type references.
-		/// The default value is <c>false</c>.
+		/// The default value is <see langword="false" />.
 		/// </summary>
 		public bool AddTypeReferenceAnnotations { get; set; }
 		
 		/// <summary>
 		/// Specifies whether the ast builder should add ResolveResult annotations to AST nodes.
-		/// The default value is <c>false</c>.
+		/// The default value is <see langword="false" />.
 		/// </summary>
 		public bool AddResolveResultAnnotations { get; set; }
 		
 		/// <summary>
 		/// Controls the accessibility modifiers are shown.
-		/// The default value is <c>true</c>.
+		/// The default value is <see langword="true" />.
 		/// </summary>
 		public bool ShowAccessibility { get; set; }
 		
 		/// <summary>
 		/// Controls the non-accessibility modifiers are shown.
-		/// The default value is <c>true</c>.
+		/// The default value is <see langword="true" />.
 		/// </summary>
 		public bool ShowModifiers { get; set; }
 		
 		/// <summary>
 		/// Controls whether base type references are shown.
-		/// The default value is <c>true</c>.
+		/// The default value is <see langword="true" />.
 		/// </summary>
 		public bool ShowBaseTypes { get; set; }
 		
 		/// <summary>
 		/// Controls whether type parameter declarations are shown.
-		/// The default value is <c>true</c>.
+		/// The default value is <see langword="true" />.
 		/// </summary>
 		public bool ShowTypeParameters { get; set; }
 
 		/// <summary>
 		/// Controls whether type parameter names are shown for unbound types.
-		/// The default value is <c>false</c>.
+		/// The default value is <see langword="false" />.
 		/// </summary>
 		public bool ShowTypeParametersForUnboundTypes { get; set; }
 		
 		/// <summary>
 		/// Controls whether constraints on type parameter declarations are shown.
 		/// Has no effect if ShowTypeParameters is false.
-		/// The default value is <c>true</c>.
+		/// The default value is <see langword="true" />.
 		/// </summary>
 		public bool ShowTypeParameterConstraints { get; set; }
 		
 		/// <summary>
 		/// Controls whether the names of parameters are shown.
-		/// The default value is <c>true</c>.
+		/// The default value is <see langword="true" />.
 		/// </summary>
 		public bool ShowParameterNames { get; set; }
 		
 		/// <summary>
 		/// Controls whether to show default values of optional parameters, and the values of constant fields.
-		/// The default value is <c>true</c>.
+		/// The default value is <see langword="true" />.
 		/// </summary>
 		public bool ShowConstantValues { get; set; }
 		
 		/// <summary>
 		/// Controls whether to show attributes.
-		/// The default value is <c>false</c>.
+		/// The default value is <see langword="false" />.
 		/// </summary>
 		public bool ShowAttributes { get; set; }
 
 		/// <summary>
 		/// Controls whether to use fully-qualified type names or short type names.
-		/// The default value is <c>false</c>.
+		/// The default value is <see langword="false" />.
 		/// </summary>
 		public bool AlwaysUseShortTypeNames { get; set; }
 
 		/// <summary>
-		/// Controls whether to use fully-qualified type names or short type names.
-		/// The default value is <c>true</c>.
+		/// Controls whether to use keywords for builtin types.
+		/// The default value is <see langword="true" />.
+		/// </summary>
+		public bool UseKeywordsForBuiltinTypes { get; set; }
+
+		/// <summary>
+		/// Controls whether to use <c>T?</c> or <c>Nullable&lt;T&gt;</c> for nullable value types.
+		/// The default value is <see langword="true" />.
 		/// </summary>
-		public bool AlwaysUseBuiltinTypeNames { get; set; }
+		public bool UseNullableSpecifierForValueTypes { get; set; }
 
 		/// <summary>
 		/// Determines the name lookup mode for converting a type name.
@@ -165,37 +172,37 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		
 		/// <summary>
 		/// Controls whether to generate a body that throws a <c>System.NotImplementedException</c>.
-		/// The default value is <c>false</c>.
+		/// The default value is <see langword="false" />.
 		/// </summary>
 		public bool GenerateBody { get; set; }
 		
 		/// <summary>
 		/// Controls whether to generate custom events.
-		/// The default value is <c>false</c>.
+		/// The default value is <see langword="false" />.
 		/// </summary>
 		public bool UseCustomEvents { get; set; }
 
 		/// <summary>
 		/// Controls whether unbound type argument names are inserted in the ast or not.
-		/// The default value is <c>false</c>.
+		/// The default value is <see langword="false" />.
 		/// </summary>
 		public bool ConvertUnboundTypeArguments { get; set;}
 
 		/// <summary>
 		/// Controls whether aliases should be used inside the type name or not.
-		/// The default value is <c>true</c>.
+		/// The default value is <see langword="true" />.
 		/// </summary>
 		public bool UseAliases { get; set; }
 
 		/// <summary>
 		/// Controls whether constants like <c>int.MaxValue</c> are converted to a <see cref="MemberReferenceExpression"/> or <see cref="PrimitiveExpression" />.
-		/// The default value is <c>true</c>.
+		/// The default value is <see langword="true" />.
 		/// </summary>
 		public bool UseSpecialConstants { get; set; }
 
 		/// <summary>
 		/// Controls whether integral constants should be printed in hexadecimal format.
-		/// The default value is <c>false</c>.
+		/// The default value is <see langword="false" />.
 		/// </summary>
 		public bool PrintIntegralValuesAsHex { get; set; }
 		#endregion
@@ -290,7 +297,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 						}
 						break;
 					case ParameterizedType pt:
-						if (AlwaysUseBuiltinTypeNames && pt.IsKnownType(KnownTypeCode.NullableOfT)) {
+						if (UseNullableSpecifierForValueTypes && pt.IsKnownType(KnownTypeCode.NullableOfT)) {
 							return ConvertType(pt.TypeArguments[0]).MakeNullableType();
 						}
 						astType = ConvertTypeHelper(pt.GenericType, pt.TypeArguments);
@@ -313,7 +320,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			Debug.Assert(typeDef != null || genericType.Kind == TypeKind.Unknown);
 			Debug.Assert(typeArguments.Count >= genericType.TypeParameterCount);
 
-			if (AlwaysUseBuiltinTypeNames && typeDef != null) {
+			if (UseKeywordsForBuiltinTypes && typeDef != null) {
 				string keyword = KnownTypeReference.GetCSharpNameByTypeCode(typeDef.KnownTypeCode);
 				if (keyword != null) {
 					return new PrimitiveType(keyword);

ICSharpCode.Decompiler/CSharp/Transforms/IntroduceUsingDeclarations.cs

@@ -116,12 +116,14 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 		{
 			readonly Stack<CSharpTypeResolveContext> context;
 			readonly bool ignoreUsingScope;
+			readonly DecompilerSettings settings;
 
 			TypeSystemAstBuilder astBuilder;
 			
 			public FullyQualifyAmbiguousTypeNamesVisitor(TransformContext context, UsingScope usingScope)
 			{
 				this.ignoreUsingScope = !context.Settings.UsingDeclarations;
+				this.settings = context.Settings;
 
 				CSharpTypeResolveContext currentContext;
 				if (ignoreUsingScope) {
@@ -139,7 +141,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				this.astBuilder = CreateAstBuilder(currentContext);
 			}
 
-			static TypeSystemAstBuilder CreateAstBuilder(CSharpTypeResolveContext context, IL.ILFunction function = null)
+			TypeSystemAstBuilder CreateAstBuilder(CSharpTypeResolveContext context, IL.ILFunction function = null)
 			{
 				CSharpResolver resolver = new CSharpResolver(context);
 				if (function != null) {
@@ -148,8 +150,9 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 							resolver = resolver.AddVariable(new DefaultVariable(v.Type, v.Name));
 					}
 				}
-				
+
 				return new TypeSystemAstBuilder(resolver) {
+					UseNullableSpecifierForValueTypes = settings.LiftNullables,
 					AddResolveResultAnnotations = true,
 					UseAliases = true
 				};

ICSharpCode.Decompiler/Output/IAmbience.cs

@@ -92,12 +92,17 @@ namespace ICSharpCode.Decompiler.Output
 		/// Show default values of parameters.
 		/// </summary>
 		ShowParameterDefaultValues = 0x4000,
+		/// <summary>
+		/// Use <c>T?</c> instead of <c>Nullable&lt;T&gt;</c>.
+		/// </summary>
+		UseNullableSpecifierForValueTypes = 0x8000,
 
 		StandardConversionFlags = ShowParameterNames |
 			ShowAccessibility |
 			ShowParameterList |
 			ShowParameterModifiers |
 			ShowParameterDefaultValues |
+			UseNullableSpecifierForValueTypes |
 			ShowReturnType |
 			ShowModifiers |
 			ShowTypeParameterList |

ILSpy/Languages/CSharpLanguage.cs

@@ -457,6 +457,9 @@ namespace ICSharpCode.ILSpy
 			CSharpAmbience ambience = new CSharpAmbience();
 			// Do not forget to update CSharpAmbienceTests.ILSpyMainTreeViewTypeFlags, if this ever changes.
 			ambience.ConversionFlags = ConversionFlags.ShowTypeParameterList | ConversionFlags.PlaceReturnTypeAfterParameterList;
+			if (new DecompilationOptions().DecompilerSettings.LiftNullables) {
+				ambience.ConversionFlags |= ConversionFlags.UseNullableSpecifierForValueTypes;
+			}
 			return ambience;
 		}
 
@@ -635,7 +638,13 @@ namespace ICSharpCode.ILSpy
 			var output = new StringWriter();
 			var decoratedWriter = new TextWriterTokenWriter(output);
 			var writer = new CSharpHighlightingTokenWriter(TokenWriter.InsertRequiredSpaces(decoratedWriter), locatable: decoratedWriter);
-			new CSharpAmbience() { ConversionFlags = flags }.ConvertSymbol(entity, writer, new DecompilerSettings().CSharpFormattingOptions);
+			var settings = new DecompilationOptions().DecompilerSettings;
+			if (!settings.LiftNullables) {
+				flags &= ~ConversionFlags.UseNullableSpecifierForValueTypes;
+			}
+			new CSharpAmbience() {
+				ConversionFlags = flags,
+			}.ConvertSymbol(entity, writer, settings.CSharpFormattingOptions);
 			return new RichText(output.ToString(), writer.HighlightingModel);
 		}