CorLibType not perserved after TokenAllocator

[JPaja]

Describe the bug

TypeReferences that are constructed by importing reflection type, are not preserved after using TokenAllocator on them.

Issue is same for allocating tokens on references generated by CorLibFactory where assembly contains typeof() of that type

To Reproduce

using AsmResolver.DotNet;
using AsmResolver.DotNet.Builder;

var module = ModuleDefinition.FromModule(typeof(Program).Module);

var importer = new ReferenceImporter(module);
var reference  = (TypeReference)importer.ImportType(typeof(int));
var reference2 = (TypeReference)importer.ImportType(typeof(void));

module.TokenAllocator.AssignNextAvailableToken(reference);
module.TokenAllocator.AssignNextAvailableToken(reference2);

var image = module.ToPEImage(new ManagedPEImageBuilder(MetadataBuilderFlags.PreserveAll));
var newModule = ModuleDefinition.FromImage(image);

var newReference = (TypeReference) newModule.LookupMember(reference.MetadataToken);
var newReference2 = (TypeReference) newModule.LookupMember(reference2.MetadataToken);

Assert.Equal(reference.Namespace, newReference.Namespace);
Assert.Equal(reference.Name, newReference.Name);
Assert.Equal(reference2.Namespace, newReference2.Namespace);
Assert.Equal(reference2.Name, newReference2.Name);

using AsmResolver.DotNet;
using AsmResolver.DotNet.Builder;
 
var module = ModuleDefinition.FromModule(typeof(Program).Module);

Type oldRef1 = typeof(int);
Type oldRef2 = typeof(void);

var reference  = (TypeReference)module.CorLibTypeFactory.Int32.ToTypeDefOrRef();
var reference2 = (TypeReference)module.CorLibTypeFactory.Void.ToTypeDefOrRef();

module.TokenAllocator.AssignNextAvailableToken(reference);
module.TokenAllocator.AssignNextAvailableToken(reference2);

var image = module.ToPEImage(new ManagedPEImageBuilder(MetadataBuilderFlags.PreserveAll));
var newModule = ModuleDefinition.FromImage(image);

var newReference = (TypeReference) newModule.LookupMember(reference.MetadataToken);
var newReference2 = (TypeReference) newModule.LookupMember(reference2.MetadataToken);

Assert.Equal(reference.Namespace, newReference.Namespace);
Assert.Equal(reference.Name, newReference.Name);
Assert.Equal(reference2.Namespace, newReference2.Namespace);
Assert.Equal(reference2.Name, newReference2.Name);

Expected behavior

newModule.LookupMember should not throw, and should return perserved TypeReference

Platform

• OS:Windows 10
• AsmResolver Version: 4.8 (nuget)

[JPaja]

Update:

Seems like this is issue persists on any type, not just CorLibTypes.
And its not limited to typeof(), any code that can generate same TypeReference in compile time can cause same issue (for eg using type in locals, arguments, return types etc..).

Example:

using AsmResolver.DotNet;
using AsmResolver.DotNet.Builder;
 
var module = ModuleDefinition.FromModule(typeof(Program).Module);
var asmResRef = module.AssemblyReferences.First(a => a.Name == "AsmResolver.DotNet");
    
Type oldRef1 = typeof(MethodDefinition);
Type oldRef2 = typeof(ModuleDefinition);

var reference  = new TypeReference(module, asmResRef, "AsmResolver.DotNet", "MethodDefinition");
var reference2 = new TypeReference(module, asmResRef, "AsmResolver.DotNet", "ModuleDefinition");

module.TokenAllocator.AssignNextAvailableToken(reference);
module.TokenAllocator.AssignNextAvailableToken(reference2);

var image = module.ToPEImage(new ManagedPEImageBuilder(MetadataBuilderFlags.PreserveAll));
var newModule = ModuleDefinition.FromImage(image);

var newReference = (TypeReference) newModule.LookupMember(reference.MetadataToken);
var newReference2 = (TypeReference) newModule.LookupMember(reference2.MetadataToken);

Assert.Equal(reference.Namespace, newReference.Namespace);
Assert.Equal(reference.Name, newReference.Name);
Assert.Equal(reference2.Namespace, newReference2.Namespace);
Assert.Equal(reference2.Name, newReference2.Name);

using AsmResolver.DotNet;
using AsmResolver.DotNet.Builder;
 
var module = ModuleDefinition.FromModule(typeof(Program).Module);
var asmResRef = module.AssemblyReferences.First(a => a.Name == "AsmResolver.DotNet");

MethodDefinition oldRef1;
MethodDefinition oldRef2;

var reference  = new TypeReference(module, asmResRef, "AsmResolver.DotNet", "MethodDefinition");
var reference2 = new TypeReference(module, asmResRef, "AsmResolver.DotNet", "ModuleDefinition");

module.TokenAllocator.AssignNextAvailableToken(reference);
module.TokenAllocator.AssignNextAvailableToken(reference2);

var image = module.ToPEImage(new ManagedPEImageBuilder(MetadataBuilderFlags.PreserveAll));
var newModule = ModuleDefinition.FromImage(image);

var newReference = (TypeReference) newModule.LookupMember(reference.MetadataToken);
var newReference2 = (TypeReference) newModule.LookupMember(reference2.MetadataToken);

My initial guess is that adding same type reference with different token to metadata table gets ignored.

Possible solutions:

• Allow duplicate type references in Metadata table
• TokenAllocator.AssignNextToken should assign old token if it finds same instance in md table (Which would cause multiple TypeReference instances with same mdtoken)