fix: library loading for swift dynamic frameworks

[bilousoleksandr]

Proposed changes

By default, Dynamic Framework doesn't create a resources bundle and packs all resources inside its own Resources folder.

To fix the issue related to SwiftPM, add try loading metal library from Framework/../Resources/default.metallib when mlx codebase is built as a dynamic framework.

Checklist

Put an x in the boxes that apply.

• I have read the CONTRIBUTING document
• I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• I have added tests that prove my fix is effective or that my feature works
• I have updated the necessary documentation (if needed)

[awni]

@davidkoski do you mind checking this change is useful for MLX Swift?

[davidkoski]

load_colocated_library will get the directory of the binary that contains the get_binary_directory(). In the case of an embedded .framework it would be something like x.app/Contents/Frameworks/MLX.framework/Versions/A. This would then append Resources/default and .metallib onto that and load the file.

I think this works if the default.metallib is hoisted out of the mlx-swift_Cmlx.bundle/Contents/Resources. I am not sure it is because I don't have a .framework wrapping the MLX swiftpm library myself, but such a thing could surely be done.

[davidkoski]

That said, I am surprised that this does not do the same thing:

std::pair<MTL::Library*, NS::Error*> load_swiftpm_library(
    MTL::Device* device,
    const std::string& lib_name) {
#ifdef SWIFTPM_BUNDLE
...
  auto bundles = NS::Bundle::allBundles();
  for (int i = 0, c = (int)bundles->count(); i < c; i++) {
    auto bundle = reinterpret_cast<NS::Bundle*>(bundles->object(i));
    library = try_load_bundle(device, bundle->resourceURL(), lib_name);

That should scan all bundles (frameworks are considered bundles) looking for a default.metallib.

[bilousoleksandr]

It doesn't work this way, because bundles doesn't contain MLX framework path. In current configuration, it always looks for for main bundle and tries to load default.metallib from mlx-swift_Cmlx.bundle. But with dynamic frameworks, app directory looks next way:

• App.app
  • Contents
    • Frameworks
      • MLX
        • Resources
          • default.metallib
    • Resources

NSBundle <~Work/DerivedData/Eney-dyyiohebtzyjuwbwalhqtrcvkvcn/Build/Products/Debug/App.app> (loaded),
NSBundle </System/Library/Extensions/AGXMetalG13X.bundle> (loaded),
NSBundle </System/Library/Input Methods/PressAndHold.app/Contents/PlugIns/PAH_Extension.appex> (not yet loaded),
NSBundle </System/Library/CoreServices/SystemAppearance.bundle> (not yet loaded)

[bilousoleksandr]

@davidkoski I've covered a questions related to load_swiftpm_library above

[davidkoski]

OK, if the default.metallib is in the Resources directory, I agree this looks good.

[davidkoski]

@davidkoski do you mind checking this change is useful for MLX Swift?

It might be, but:

1. I don't have a good way to test it as I don't have a framework wrapped MLX and it seems to require a particular layout of the framework
2. the existing load_swiftpm_library ought to do something identical when it scans the bundles -- I wonder why this didn't work?

[angeloskath]

This looks fine to me also given the discussion and @davidkoski 's agreement, so I 'll merge after the tests clear.

[angeloskath]

@bilousoleksandr the NS::Error error[4] needs to be NS::Error error[5].

[bilousoleksandr]

@bilousoleksandr the NS::Error error[4] needs to be NS::Error error[5].

Fixed

[bilousoleksandr]

@angeloskath could you re-approve the PR to enable CI run?