[MLX] Probe the usable Metal compiler in Apple CMake presets
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@metascroy is already working on this.
Since Sep 10, 2026.
bug
module: build/install
module: mlx
- Dominant language
- Python
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Description
Problem
The Apple and pybind presets use xcrun -sdk macosx --find metal. On current Xcode releases this can locate a launcher even when the separately installed Metal Toolchain component is unavailable, so configuration enables MLX and fails later during compilation.
The documentation correction is part of #22620. The preset behavior change is intentionally excluded from that documentation-only PR.
Proposed change
Probe xcrun -sdk macosx metal --version in both presets and update the fallback message to point to xcodebuild -downloadComponent MetalToolchain.
Test plan
- Configure on Apple silicon with Xcode and the Metal Toolchain installed; verify MLX remains enabled.
- Configure with Xcode but without the Metal Toolchain; verify MLX is disabled cleanly.
- Run Apple pybind and MLX build CI.
cc @larryliu0820 @GregoryComer @metascroy
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