[API Proposal]: MetadataLoadContext.GetLoadContext(Assembly)

[IS4Code]

Background and motivation

Unlike AssemblyLoadContext, the similarly named MetadataLoadContext does not have the GetLoadContext method that allows retrieving the original load context from its corresponding Assembly instance. This is inconvenient in situations such as when calling assembly.GetReferencedAssemblies() and attempting to resolve the AssemblyName instances.

The relevant property is already there, just internal and thus inaccessible.

API Proposal

using System.Reflection.TypeLoading;

namespace System.Reflection;

public class MetadataLoadContext
{
    public static MetadataLoadContext? GetLoadContext(Assembly assembly)
    {
        ArgumentNullException.ThrowIfNull(assembly);
 
        return (assembly as RoAssembly)?.Loader;
    }
}

API Usage

var context = new MetadataLoadContext(...);
var asm = context.LoadFromAssemblyName(...);
Assert.AreEqual(MetadataLoadContext.GetLoadContext(asm), context);

Alternative Designs

Another option, with arguably greater impact but also requirements, would be to make the Assembly class expose its loader through a public property, probably as an interface which both AssemblyLoadContext and MetadataLoadContext would implement. This would work with any potential new load context type, but requires modifying Assembly and thus would not work easily with older platforms, unlike just modifying MetadataLoadContext which is released as a package. It could however remain a possibility even with this API added.

Risks

By accessing the MetadataLoadContext of an Assembly, code may load any arbitrary assemblies into the context, but the related AssemblyLoadContext already provides this functionality where it may be more dangerous than here, and the Loader property is accessible by reflection anyway.

Tagging subscribers to this area: @vitek-karas, @agocke, @VSadov
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Background and motivation

Unlike AssemblyLoadContext, the similarly named MetadataLoadContext does not have the GetLoadContext method that allows retrieving the original load context from its corresponding Assembly instance. This is inconvenient in situations such as when calling assembly.GetReferencedAssemblies() and attempting to resolve the AssemblyName instances.

The relevant property is already there, just internal and thus inaccessible.

API Proposal

using System.Reflection.TypeLoading;

namespace System.Reflection;

class MetadataLoadContext
{
    public static MetadataLoadContext? GetLoadContext(Assembly assembly)
    {
        ArgumentNullException.ThrowIfNull(assembly);
 
        return (assembly as RoAssembly)?.Inner;
    }
}

API Usage

var context = new MetadataLoadContext(...);
var asm = context.LoadFromAssemblyName(...);
Assert.AreEqual(MetadataLoadContext.GetLoadContext(asm), context);

Alternative Designs

Another option, with arguably greater impact but also requirements, would be to make the Assembly class expose its loader through a public property, probably as an interface which both AssemblyLoadContext and MetadataLoadContext would implement. This would work with any potential new load context type, but requires modifying Assembly and thus would not work easily with older platforms, unlike just modifying MetadataLoadContext which is released as a package. It could however remain a possibility even with this API added.

Risks

By accessing the MetadataLoadContext of an Assembly, code may load any arbitrary assemblies into the context, but the related AssemblyLoadContext already provides this functionality where it may be more dangerous than here, and the Loader property is accessible by reflection anyway.

Author:	IS4Code
Assignees:	-
Labels:	api-suggestion, area-AssemblyLoader-coreclr, untriaged
Milestone:	-

Tagging subscribers to this area: @dotnet/area-system-reflection
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Background and motivation

Unlike AssemblyLoadContext, the similarly named MetadataLoadContext does not have the GetLoadContext method that allows retrieving the original load context from its corresponding Assembly instance. This is inconvenient in situations such as when calling assembly.GetReferencedAssemblies() and attempting to resolve the AssemblyName instances.

The relevant property is already there, just internal and thus inaccessible.

API Proposal

using System.Reflection.TypeLoading;

namespace System.Reflection;

class MetadataLoadContext
{
    public static MetadataLoadContext? GetLoadContext(Assembly assembly)
    {
        ArgumentNullException.ThrowIfNull(assembly);
 
        return (assembly as RoAssembly)?.Inner;
    }
}

API Usage

var context = new MetadataLoadContext(...);
var asm = context.LoadFromAssemblyName(...);
Assert.AreEqual(MetadataLoadContext.GetLoadContext(asm), context);

Alternative Designs

Another option, with arguably greater impact but also requirements, would be to make the Assembly class expose its loader through a public property, probably as an interface which both AssemblyLoadContext and MetadataLoadContext would implement. This would work with any potential new load context type, but requires modifying Assembly and thus would not work easily with older platforms, unlike just modifying MetadataLoadContext which is released as a package. It could however remain a possibility even with this API added.

Risks

By accessing the MetadataLoadContext of an Assembly, code may load any arbitrary assemblies into the context, but the related AssemblyLoadContext already provides this functionality where it may be more dangerous than here, and the Loader property is accessible by reflection anyway.

Author:	IS4Code
Assignees:	-
Labels:	api-suggestion, area-System.Reflection, area-AssemblyLoader-coreclr, untriaged
Milestone:	-

[jkotas]

@steveharter This proposal looks good to me. Mark is as api-ready-to-review?

[bartonjs]

Video

• We questioned whether it should be TryGetLoadContext, but decided it was OK as-is.

namespace System.Reflection;

public partial class MetadataLoadContext
{
    public static MetadataLoadContext? GetLoadContext(Assembly assembly);
}