Injecting GeneratedCodeAttribute with Mono.Cecil

Question

I'm manupulating my .net 2.0 assemblies with Mono.Cecil. After manipulation I want to mark assembly as processed by injecting a module attribute

var stringType = _module.Import(typeof(string));
var baseCtor = _module.Import(typeof(GeneratedCodeAttribute).GetConstructor(new[] { typeof(string), typeof(string) }));
var result = new CustomAttribute(baseCtor);
result.ConstructorArguments.Add(new CustomAttributeArgument(stringType, "ProcessedBySomething"));
result.ConstructorArguments.Add(new CustomAttributeArgument(stringType, "1.0"));

After saving the assembly it become dependent on .net 4.0, since manipulating app is written in .net 4.0. GeneratedCodeAttribute exists in .net 2.0, so what am I doing wrong?

Answer 1

You're guessing right. Since the manipulating application is running on .net 4.0, typeof being a runtime feature, it will return a type for the current runtime version.

To fix it, the simple thing to do is to create references for the mscorlib version referenced by the module you're modifying, using Cecil to open the assembly. Your code would become:

var stringType = _module.TypeSystem.String;
var corlib = (AssemblyNameReference) _module.TypeSystem.Corlib;
var system = _module.AssemblyResolver.Resolve (new AssemblyNameReference ("System", corlib.Version) {
    PublicKeyToken = corlib.PublicKeyToken,
});
var generatedCodeAttribute = system.MainModule.GetType ("System.CodeDom.Compiler.GeneratedCodeAttribute");
var generatedCodeCtor = generatedCodeAttribute.Methods.First (m => m.IsConstructor && m.Parameters.Count == 2);

var result = new CustomAttribute (_module.Import (generatedCodeCtor));
result.ConstructorArguments.Add(new CustomAttributeArgument(stringType, "ProcessedBySomething"));
result.ConstructorArguments.Add(new CustomAttributeArgument(stringType, "1.0"));