Allowing SPM to compile on Linux with CUDA

[gmondada]

Proposed changes

This PR introduces an SPM plug-in allowing CUDA to be compiled by SPM on Linux.

Example1 can be compiled on Linux with command:

swift build --product Example1

SPM invokes nvcc, therefore you need the CUDA toolkit to be installed.

A few notes:

• You need at least CUDA 13.2. Version 12 has a very limited support for clang.
• This solution rely on “CGen” SPM experimental feature, which is only available in Swift 6.3.
• Code generated at compile time is managed by tools/update-mlx.sh.
• On my computer I need to compile with --jobs=2 for limiting the memory required during compilation. Solutions to mitigate this will be proposed in further PRs.

Checklist

• 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)

[gmondada]

@davidkoski @Joannis 👆

[gmondada]

To compile with CUDA on Mac, just create a docker with https://github.com/gmondada/cuda-toolkit-docker/blob/main/Dockerfile.ubuntu24

[davidkoski]

Xcode 26.3
...
package 'mlx-swift' is using Swift tools version 6.3.0 but the installed version is 6.2.4

Let me see if we have Xcode 26.4 available in CI.

[davidkoski]

See #414 -- it looks like we can use the latest or a particular version of Xcode:

        env:
          DEVELOPER_DIR: /Applications/Xcode-latest.app

this should be done for all the steps that do xcodebuild or xcrun

[davidkoski]

@gmondada FYI

See #414 -- it looks like we can use the latest or a particular version of Xcode:

        env:
          DEVELOPER_DIR: /Applications/Xcode-latest.app

this should be done for all the steps that do xcodebuild or xcrun

We have the newer Xcode available in CI but it isn't the default, so we need this for it to run.

[davidkoski]

/Users/runner/actions-runner/_work/mlx-swift/mlx-swift/Source/MLX/GPU+CUDA.swift:14:13: error: invalid redeclaration of 'GPU'
public enum GPU {
            ^
/Users/runner/actions-runner/_work/mlx-swift/mlx-swift/Source/MLX/GPU+Metal.swift:15:13: note: 'GPU' previously declared here
public enum GPU {
            ^
/Users/runner/actions-runner/_work/mlx-swift/mlx-swift/Source/MLX/GPU+Metal.swift:15:13: note: 'GPU' previously declared here
public enum GPU {
            ^

looks like this might be a file exclusion issue on macOS (apple platforms probably).

[gmondada]

Oh, I didn't notice this compilation issue and wasn't aware of the Xcode project. Thanks for bringing this to my attention. Should work now.

[gmondada]

... and didn't update the CMake build system. Now done.

[davidkoski]

Why have one build system when you could have 3?

[davidkoski]

Build is clean in CI, thank you so much for your work on this!