metal-cpp: Add header only library metal-cpp from Apple

[irieger]

Specify library name and version: metal-cpp/x

Add metal-cpp header only library provided by Apple under the Apache 2.0 license: https://developer.apple.com/metal/cpp/

This library wraps some libraries provided by Apple as Objective-C interfaces into C++ interfaces. Headers only provide the wrapping and it requires one file doing the implementation (as described on the linked project page).

Important point: No clear versioning, packages only reference the version of the macOS/iOS SDKs they wrap into C++. Also the library requires relatively modern macOS/iOS versions to be compiled.

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• I've read the contributing guidelines.
• I've used a recent Conan client version close to the currently deployed.
• I've tried at least one configuration locally with the conan-center hook activated.

[irieger]

Pinging #17848 here

I use metal-cpp myself and currently copy the headers into my project which I'd like to prevent, which is why I want to have it as a library myself.

[irieger]

Some open questions to discuss:

1. Version naming: Current suggestion uses the version number of the target macOS version of the headers as the version number. Would it be better to use cci.xyz or something else?
2. Version checking and settings are a bit unclear to me here. "Building" the header only library obviously just requires unpacking the ZIP and packing it into a conan package. Applying it however depends mainly on the target SDK, so version "13" builds on everything targeting macOS 13 or newer, while version "14.2" requires a config with "os.version=14.2". How to best reflect this?

[jcar87]

Hi @irieger - thank you so much for this PR and for investigating and troubleshooting the SDK version compatibility.

I have pushed a couple refactorings in this PR - while your PR is correct, I think requiring the users to have os.version or os.sdk_version defined may be a tad too far, as doing so would cause all package IDs to be different due to the new settings, and it may be incompatible with what they had before.

As a fallback, I'm proposing to ask xcrun what the version of the SDK is - it is the SDK headers after all that define the compatible versions of macOS (and others). This should work in most cases when the other two are not defined, and should return the baseline SDK version (which is what ultimately will determine whether the required link libraries are available). One is to assume that if xcrun returns this SDK version, this is what will be used de-facto and that the target OS version will typically be just this (or lower), and if the user wants a target version - they would use os.version anyway.

Additionally - added checks for tvOS as well, since it falls under the "iOS" umbrella (if I'm not mistaken, iOS in this context is both iOS and ipadOS, and tvOS is versioned alongside those two). I've moved the dict of versions to Conandata.yml - as that seems to be a better place for "version-dependent" information.

[irieger]

Hey @jcar87 thank you for the proposed changes. I think they make sense.

I just fixed one version requirement and did a small cleanup but from my point of view we could move forward.

Build all 4 versions locally with success.

[conan-center-bot]

Conan v1 pipeline ✔️

All green in build 20 (b3f415f59a94488389268e533ed0ad3488e3f7a8):

• metal-cpp/13.3:
  All packages built successfully! (All logs)

• metal-cpp/14.2:
  All packages built successfully! (All logs)

• metal-cpp/13:
  All packages built successfully! (All logs)

• metal-cpp/14:
  All packages built successfully! (All logs)

---

Conan v2 pipeline ✔️

Note: Conan v2 builds are now mandatory. Please read our discussion about it.

All green in build 19 (b3f415f59a94488389268e533ed0ad3488e3f7a8):

• metal-cpp/14.2:
  All packages built successfully! (All logs)

• metal-cpp/13.3:
  All packages built successfully! (All logs)

• metal-cpp/14:
  All packages built successfully! (All logs)

• metal-cpp/13:
  All packages built successfully! (All logs)

[jcar87]

Hey @jcar87 thank you for the proposed changes. I think they make sense.

I just fixed one version requirement and did a small cleanup but from my point of view we could move forward.

Build all 4 versions locally with success.

Thanks so much!

[irieger]

Nice. Thank you very much for the review and the general work. Working on my side projects is so much more fun now since I switched everything to conan.