Add test for C# 8 nullable reference types; and fix some bugs.

ICSharpCode.Decompiler.Tests/Helpers/RemoveCompilerAttribute.cs

@@ -39,6 +39,7 @@ namespace ICSharpCode.Decompiler.Tests.Helpers
 			"System.Runtime.CompilerServices.IsReadOnlyAttribute",
 			"System.Runtime.CompilerServices.IsByRefLikeAttribute",
 			"System.Runtime.CompilerServices.IsUnmanagedAttribute",
+			"System.Runtime.CompilerServices.NullableAttribute",
 			"Microsoft.CodeAnalysis.EmbeddedAttribute",
 		};
 

ICSharpCode.Decompiler.Tests/Helpers/Tester.cs

@@ -245,7 +245,10 @@ namespace ICSharpCode.Decompiler.Tests.Helpers
 			var preprocessorSymbols = GetPreprocessorSymbols(flags);
 
 			if (flags.HasFlag(CompilerOptions.UseRoslyn)) {
-				var parseOptions = new CSharpParseOptions(preprocessorSymbols: preprocessorSymbols.ToArray(), languageVersion: Microsoft.CodeAnalysis.CSharp.LanguageVersion.Latest);
+				var parseOptions = new CSharpParseOptions(
+					preprocessorSymbols: preprocessorSymbols.ToArray(),
+					languageVersion: Microsoft.CodeAnalysis.CSharp.LanguageVersion.CSharp8
+				);
 				var syntaxTrees = sourceFileNames.Select(f => SyntaxFactory.ParseSyntaxTree(File.ReadAllText(f), parseOptions, path: f));
 				var references = defaultReferences.Value;
 				if (flags.HasFlag(CompilerOptions.ReferenceVisualBasic)) {

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

@@ -85,6 +85,7 @@
     <Compile Include="TestCases\ILPretty\Issue1323.cs" />
     <Compile Include="TestCases\Pretty\CustomAttributes2.cs" />
     <Compile Include="TestCases\Pretty\EnumTests.cs" />
+    <None Include="TestCases\Pretty\NullableRefTypes.cs" />
     <Compile Include="TestCases\Pretty\TypeMemberTests.cs" />
     <Compile Include="TestCases\Pretty\ValueTypes.cs" />
     <None Include="TestCases\ILPretty\Issue1389.il" />

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -289,6 +289,12 @@ namespace ICSharpCode.Decompiler.Tests
 			Run(cscOptions: cscOptions);
 		}
 
+		[Test]
+		public void NullableRefTypes([ValueSource(nameof(roslynOnlyOptions))] CompilerOptions cscOptions)
+		{
+			RunForLibrary(cscOptions: cscOptions);
+		}
+
 		[Test]
 		public void NullPropagation([ValueSource(nameof(roslynOnlyOptions))] CompilerOptions cscOptions)
 		{

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

@@ -0,0 +1,31 @@
+#nullable enable
+using System.Collections.Generic;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	public class NullableRefTypes
+	{
+		private string field_string;
+		private string? field_nullable_string;
+
+		private Dictionary<string?, string> field_generic;
+		private (string, string?, string) field_tuple;
+		private string[]?[] field_array;
+		private Dictionary<(string, string?), (int, string[]?, string?[])> field_complex;
+
+		public int GetLength1(string[] arr)
+		{
+			return field_string.Length + arr.Length;
+		}
+
+		public int GetLength2(string[]? arr)
+		{
+			return field_nullable_string!.Length + arr!.Length;
+		}
+
+		public int? GetLength3(string[]? arr)
+		{
+			return field_nullable_string?.Length + arr?.Length;
+		}
+	}
+}

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -1777,11 +1777,7 @@ namespace ICSharpCode.Decompiler.CSharp
 							.WithRR(new ResolveResult(NullableType.GetUnderlyingType(translatedTarget.Type)))
 							.WithoutILInstruction();
 					}
-					if (translatedTarget.Type.Nullability == Nullability.Nullable) {
-						translatedTarget = new UnaryOperatorExpression(UnaryOperatorType.SuppressNullableWarning, translatedTarget)
-							.WithRR(new ResolveResult(translatedTarget.Type.ChangeNullability(Nullability.Oblivious)))
-							.WithoutILInstruction();
-					}
+					translatedTarget = EnsureTargetNotNullable(translatedTarget);
 					return translatedTarget;
 				}
 			} else {
@@ -1790,7 +1786,20 @@ namespace ICSharpCode.Decompiler.CSharp
 					.WithRR(new TypeResolveResult(memberDeclaringType));
 			}
 		}
-		
+
+		private TranslatedExpression EnsureTargetNotNullable(TranslatedExpression expr)
+		{
+			if (expr.Type.Nullability == Nullability.Nullable) {
+				if (expr.Expression is UnaryOperatorExpression uoe && uoe.Operator == UnaryOperatorType.NullConditional) {
+					return expr;
+				}
+				return new UnaryOperatorExpression(UnaryOperatorType.SuppressNullableWarning, expr)
+					.WithRR(new ResolveResult(expr.Type.ChangeNullability(Nullability.Oblivious)))
+					.WithoutILInstruction();
+			}
+			return expr;
+		}
+
 		protected internal override TranslatedExpression VisitLdObj(LdObj inst, TranslationContext context)
 		{
 			var target = Translate(inst.Target);
@@ -1875,6 +1884,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			if (arrayExpr.Type.Kind != TypeKind.Array) {
 				arrayExpr = arrayExpr.ConvertTo(compilation.FindType(KnownTypeCode.Array), this);
 			}
+			arrayExpr = EnsureTargetNotNullable(arrayExpr);
 			if (inst.ResultType == StackType.I4) {
 				return new MemberReferenceExpression(arrayExpr.Expression, "Length")
 					.WithILInstruction(inst)

ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs

@@ -243,7 +243,11 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 				if (typeWithElementType is PointerType) {
 					return ConvertType(typeWithElementType.ElementType).MakePointerType();
 				} else if (typeWithElementType is ArrayType) {
-					return ConvertType(typeWithElementType.ElementType).MakeArrayType(((ArrayType)type).Dimensions);
+					var astType = ConvertType(typeWithElementType.ElementType).MakeArrayType(((ArrayType)type).Dimensions);
+					if (type.Nullability == Nullability.Nullable)
+						return astType.MakeNullableType();
+					else
+						return astType;
 				} else if (typeWithElementType is ByReferenceType) {
 					return ConvertType(typeWithElementType.ElementType).MakeRefType();
 				} else {

ICSharpCode.Decompiler/IL/Transforms/NullPropagationTransform.cs

@@ -210,6 +210,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					// ensure the access chain does not contain any 'nullable.unwrap' that aren't directly part of the chain
 					if (ArgumentsAfterFirstMayUnwrapNull(call.Arguments))
 						return false;
+				} else if (inst is LdLen ldLen) {
+					inst = ldLen.Array;
 				} else if (inst is NullableUnwrap unwrap) {
 					inst = unwrap.Argument;
 				} else if (inst is DynamicGetMemberInstruction dynGetMember) {

ICSharpCode.Decompiler/TypeSystem/ApplyAttributeTypeVisitor.cs

@@ -186,11 +186,13 @@ namespace ICSharpCode.Decompiler.TypeSystem
 						int normalArgCount = Math.Min(type.TypeArguments.Count, TupleType.RestPosition - 1);
 						for (int i = 0; i < normalArgCount; i++) {
 							dynamicTypeIndex++;
+							nullabilityTypeIndex++;
 							elementTypes.Add(type.TypeArguments[i].AcceptVisitor(this));
 						}
 						if (type.TypeArguments.Count == TupleType.RestPosition) {
 							type = type.TypeArguments.Last() as ParameterizedType;
 							dynamicTypeIndex++;
+							nullabilityTypeIndex++;
 							if (type != null && TupleType.IsTupleCompatible(type, out int nestedCardinality)) {
 								tupleTypeIndex += nestedCardinality;
 							} else {

ICSharpCode.Decompiler/TypeSystem/ArrayType.cs

@@ -89,7 +89,19 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			ArrayType a = other as ArrayType;
 			return a != null && elementType.Equals(a.elementType) && a.dimensions == dimensions && a.nullability == nullability;
 		}
-		
+
+		public override string ToString()
+		{
+			switch (nullability) {
+				case Nullability.Nullable:
+					return elementType.ToString() + NameSuffix + "?";
+				case Nullability.NotNullable:
+					return elementType.ToString() + NameSuffix + "!";
+				default:
+					return elementType.ToString() + NameSuffix;
+			}
+		}
+
 		public override IEnumerable<IType> DirectBaseTypes {
 			get {
 				List<IType> baseTypes = new List<IType>();
@@ -125,7 +137,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			else
 				return compilation.FindType(KnownTypeCode.Array).GetMethods(typeArguments, filter, options);
 		}
-		
+
 		public override IEnumerable<IMethod> GetAccessors(Predicate<IMethod> filter = null, GetMemberOptions options = GetMemberOptions.None)
 		{
 			if ((options & GetMemberOptions.IgnoreInheritedMembers) == GetMemberOptions.IgnoreInheritedMembers)