Fix order of DirectBaseTypes and typo in SpecializedParameter

ICSharpCode.Decompiler.Tests/TypeSystem/TypeSystemLoaderTests.cs

@@ -1082,6 +1082,33 @@ namespace ICSharpCode.Decompiler.Tests.TypeSystem
 			Assert.That(prop.Setter.IsOverridable, Is.True);
 		}
 
+		[Test]
+		public void InterfaceShouldDeriveFromObject()
+		{
+			ITypeDefinition type = GetTypeDefinition(typeof(IInterfaceWithProperty));
+			Assert.That(type.DirectBaseTypes.Count() == 1, "Should have exactly one direct base type");
+			Assert.That(type.DirectBaseTypes.First().IsKnownType(KnownTypeCode.Object), "Base type should be object");
+		}
+
+		[Test]
+		public void InterfaceShouldDeriveFromObject2()
+		{
+			ITypeDefinition type = GetTypeDefinition(typeof(IShadowTestDerived));
+			Assert.That(type.DirectBaseTypes.Count() == 2, "Should have exactly two direct base types");
+			Assert.That(type.DirectBaseTypes.First() == GetTypeDefinition(typeof(IShadowTestBase)), "Base type should be IShadowTestBase");
+			Assert.That(type.DirectBaseTypes.Skip(1).First().IsKnownType(KnownTypeCode.Object), "Base type should be object");
+		}
+
+		[Test]
+		public void CheckInterfaceDirectBaseTypes()
+		{
+			ITypeDefinition type = GetTypeDefinition(typeof(IDerived));
+			Assert.That(type.DirectBaseTypes.Count() == 3, "Should have exactly three direct base types");
+			Assert.That(type.DirectBaseTypes.First() == GetTypeDefinition(typeof(IBase1)), "Base type should be IBase1");
+			Assert.That(type.DirectBaseTypes.Skip(1).First() == GetTypeDefinition(typeof(IBase2)), "Base type should be IBase2");
+			Assert.That(type.DirectBaseTypes.Skip(2).First().IsKnownType(KnownTypeCode.Object), "Base type should be object");
+		}
+
 		[Test]
 		public void VirtualPropertyAccessorsShouldNotBeOverrides()
 		{

ICSharpCode.Decompiler.Tests/TypeSystem/TypeSystemTestCase.cs

@@ -260,6 +260,21 @@ namespace ICSharpCode.Decompiler.Tests.TypeSystem
 		int Prop { get; set; }
 	}
 
+	public interface IBase1
+	{
+		int Prop { get; set; }
+	}
+
+	public interface IBase2
+	{
+		int Prop { get; set; }
+	}
+
+	public interface IDerived : IBase1, IBase2
+	{
+		int Prop { get; set; }
+	}
+
 	public class ClassWithVirtualProperty
 	{
 		public virtual int Prop { get; protected set; }

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataTypeDefinition.cs

@@ -261,13 +261,17 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 				var context = new GenericContext(TypeParameters);
 				var interfaceImplCollection = td.GetInterfaceImplementations();
 				baseTypes = new List<IType>(1 + interfaceImplCollection.Count);
-				if (!td.BaseType.IsNil) {
-					baseTypes.Add(assembly.ResolveType(td.BaseType, context));
-				}
 				foreach (var h in interfaceImplCollection) {
 					var iface = metadata.GetInterfaceImplementation(h);
 					baseTypes.Add(assembly.ResolveType(iface.Interface, context, iface.GetCustomAttributes()));
 				}
+				if (!td.BaseType.IsNil) {
+					baseTypes.Add(assembly.ResolveType(td.BaseType, context));
+				} else if (Kind == TypeKind.Interface) {
+					// td.BaseType.IsNil is always true for interfaces,
+					// but the type system expects every interface to derive from System.Object as well.
+					baseTypes.Add(Compilation.FindType(KnownTypeCode.Object));
+				}
 				return LazyInit.GetOrSet(ref this.directBaseTypes, baseTypes);
 			}
 		}

ICSharpCode.Decompiler/TypeSystem/Implementation/SpecializedParameter.cs

@@ -37,7 +37,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 
 		IReadOnlyList<IAttribute> IParameter.Attributes => baseParameter.Attributes;
 		bool IParameter.IsRef => baseParameter.IsRef;
-		bool IParameter.IsOut => baseParameter.IsOptional;
+		bool IParameter.IsOut => baseParameter.IsOut;
 		bool IParameter.IsParams => baseParameter.IsParams;
 		bool IParameter.IsOptional => baseParameter.IsOptional;
 		IParameterizedMember IParameter.Owner => newOwner;