Fix #1231: System.BadImageFormatException: Invalid coded index

ICSharpCode.Decompiler/Disassembler/ReflectionDisassembler.cs

@@ -1274,13 +1274,15 @@ namespace ICSharpCode.Decompiler.Disassembler
 			output.MarkFoldStart(defaultCollapsed: !ExpandMemberDefinitions && isInType);
 			output.WriteLine();
 
-			if (!typeDefinition.BaseType.IsNil) {
+			EntityHandle baseType = typeDefinition.GetBaseTypeOrNil();
+			if (!baseType.IsNil) {
 				output.Indent();
 				output.Write("extends ");
-				typeDefinition.BaseType.WriteTo(module, output, genericContext, ILNameSyntax.TypeName);
+				baseType.WriteTo(module, output, genericContext, ILNameSyntax.TypeName);
 				output.WriteLine();
 				output.Unindent();
 			}
+
 			var interfaces = typeDefinition.GetInterfaceImplementations();
 			if (interfaces.Count > 0) {
 				output.Indent();

ICSharpCode.Decompiler/SRMExtensions.cs

@@ -31,7 +31,7 @@ namespace ICSharpCode.Decompiler
 
 		public static bool IsValueType(this TypeDefinition typeDefinition, MetadataReader reader)
 		{
-			var baseType = typeDefinition.BaseType;
+			EntityHandle baseType = typeDefinition.GetBaseTypeOrNil();
 			if (baseType.IsNil)
 				return false;
 			if (baseType.IsKnownType(reader, KnownTypeCode.Enum))
@@ -49,9 +49,10 @@ namespace ICSharpCode.Decompiler
 
 		public static bool IsEnum(this TypeDefinition typeDefinition, MetadataReader reader)
 		{
-			if (typeDefinition.BaseType.IsNil)
+			EntityHandle baseType = typeDefinition.GetBaseTypeOrNil();
+			if (baseType.IsNil)
 				return false;
-			return typeDefinition.BaseType.IsKnownType(reader, KnownTypeCode.Enum);
+			return baseType.IsKnownType(reader, KnownTypeCode.Enum);
 		}
 
 		public static bool IsEnum(this TypeDefinitionHandle handle, MetadataReader reader, out PrimitiveTypeCode underlyingType)
@@ -62,9 +63,10 @@ namespace ICSharpCode.Decompiler
 		public static bool IsEnum(this TypeDefinition typeDefinition, MetadataReader reader, out PrimitiveTypeCode underlyingType)
 		{
 			underlyingType = 0;
-			if (typeDefinition.BaseType.IsNil)
+			EntityHandle baseType = typeDefinition.GetBaseTypeOrNil();
+			if (baseType.IsNil)
 				return false;
-			if (!typeDefinition.BaseType.IsKnownType(reader, KnownTypeCode.Enum))
+			if (!baseType.IsKnownType(reader, KnownTypeCode.Enum))
 				return false;
 			var field = reader.GetFieldDefinition(typeDefinition.GetFields().First());
 			var blob = reader.GetBlobReader(field.Signature);
@@ -81,7 +83,7 @@ namespace ICSharpCode.Decompiler
 
 		public static bool IsDelegate(this TypeDefinition typeDefinition, MetadataReader reader)
 		{
-			var baseType = typeDefinition.BaseType;
+			var baseType = typeDefinition.GetBaseTypeOrNil();
 			return !baseType.IsNil && baseType.IsKnownType(reader, KnownTypeCode.MulticastDelegate);
 		}
 		
@@ -411,5 +413,14 @@ namespace ICSharpCode.Decompiler
 				return reader.GetTypeSpecification(handle).DecodeSignature(this, genericContext);
 			}
 		}
+
+		public static EntityHandle GetBaseTypeOrNil(this TypeDefinition definition)
+		{
+			try {
+				return definition.BaseType;
+			} catch (BadImageFormatException) {
+				return default;
+			}
+		}
 	}
 }

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataTypeDefinition.cs

@@ -270,8 +270,9 @@ 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) {
+				EntityHandle baseType = td.GetBaseTypeOrNil();
-					baseTypes.Add(module.ResolveType(td.BaseType, context));
+				if (!baseType.IsNil) {
+					baseTypes.Add(module.ResolveType(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.

ILSpy/TreeNodes/DerivedTypesTreeNode.cs

@@ -76,7 +76,8 @@ namespace ICSharpCode.ILSpy.TreeNodes
 						if (IsSameType(metadata, ifaceImpl.Interface, definitionMetadata, metadataToken))
 							yield return new DerivedTypesEntryNode(list, assembly.GetDefinition(h));
 					}
-					if (!td.BaseType.IsNil && IsSameType(metadata, td.BaseType, definitionMetadata, metadataToken)) {
+					SRM.EntityHandle baseType = td.GetBaseTypeOrNil();
+					if (!baseType.IsNil && IsSameType(metadata, baseType, definitionMetadata, metadataToken)) {
 						yield return new DerivedTypesEntryNode(list, assembly.GetDefinition(h));
 					}
 				}