Mono.Cecil Exception thrown when analyzing .NET 4.5 version of System.Xml DLL, why?

Question

I'm using Mono.Cecil 0.9.5.3, and after installing VS2012 RC (which causes the .NET 4.0 System.XML.DLL to be replaced with its .NET 4.5 counterpart), I get an System.ArugmentException in some code that iterates each methods' custom attributes. It appears the cause is that in certain cases, the AsyncStateMachine attribute's ctor argument, which should be a Type, is empty.

The following piece of code reproduces it:

string path = Assembly.Load("System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089").Location;

AssemblyDefinition systemXmlAssembly = AssemblyDefinition.ReadAssembly(path);

var query =

    from ModuleDefinition module in systemXmlAssembly.Modules
    from TypeDefinition td in module.Types
    from MethodDefinition method in td.Methods
    from CustomAttribute att in method.CustomAttributes
    where method.Name == "System.Xml.IDtdParser.ParseInternalDtdAsync" &&
            att.AttributeType.Name == "AsyncStateMachineAttribute"
    select att;

CustomAttribute attribute = query.Single();

var args = attribute.ConstructorArguments; // <---- this line throws an ArgumentException

The exception is thrown from

Mono.Cecil.ModuleDefinition.CheckFullName(string fullName = "")

My question is - is this a bug in Mono.Cecil, or the System.Xml.DLL? Does the spec allow for an "empty" Type to appear as the ctor argument?

Answer 1

Looks like a bug in Cecil to me, in the sense that Cecil should read that without crashing.

Can you file a bug at https://github.com/jbevain/cecil and upload the 4.5 System.XML.dll somewhere? I'll have a look then, and report whether it's an actual Cecil issue, or a wrongly encoded custom attribute in System.XML.

Update:

It was indeed an issue with Cecil. It's now fixed in master. You'll have to build Cecil yourself until a new nuget package is released. Thanks!