Add apple tvos support

[lcruz99]

What does this PR do

This PR allows using nix lib to target tier 3 *-apple builds:

• Apple tvOS on aarch64
• Apple tvOS Simulator on x86_64

Checklist:

• I have read CONTRIBUTING.md
• I have written necessary tests and rustdoc comments
• A change log has been added if this PR modifies nix's API

[lcruz99]

tvOS build is failing because parking_lot 0.12.0 doesn't yet support this target, next release will do though.

Will drop CI job commit.

[asomers]

Instead of adding more code to support tvos, how about we remove code? By replacing every instance of:
#[cfg(any(target_os = "macos", target_os = "ios"))]
with
#[cfg(target_vendor = "apple")].
I think that should work.

[asomers]

Should there be a tvos here?

[SteveLauC]

Instead of adding more code to support tvos, how about we remove code? By replacing every instance of: #[cfg(any(target_os = "macos", target_os = "ios"))] with #[cfg(target_vendor = "apple")]. I think that should work.

Will target_vendor = "apple" contain the watchos? I didn't find any doc on what this target_vendor will be but per the Platform Support doc, watchos is also one of the Apple OSes that Rust supports

Another thing I found while searching is that the Rust team will deprecate the target_vendor attribute in the future, though I believe it is still usable for now

[asomers]

Another thing I found while searching is that the Rust team will deprecate the target_vendor attribute in the future, though I believe it is still usable for now

That is highly annoying. And it looks like the proposed target_family = apple doesn't exist yet. So deprecating target_vendor is a real step backwards in terms of usability. I wonder, can we create a build.rs script that defines our own cfg variable? Something like #[cfg(apple)] when building for any apple target?

[SteveLauC]

I wonder, can we create a build.rs script that defines our own cfg variable? Something like #[cfg(apple)] when building for any apple target?

There is a crate cfg_aliases, which seems to be exactly what we want:

// in our `build.rs`

use cfg_aliases::cfg_aliases;

fn main() {
    cfg_aliases! {
        ios: { target_os = "ios" },
        macos: { target_os = "macos" },
        watchos: { target_os = "watchos" },
        tvos: { target_os = "tvos" },
        apple_targets: { any(ios, macos, watchos, tvos) },
    }
}

Then we can use cfg(apple_targets) to conditionally compile for these apple targets

And it seems to be compatiable with the cfg attributes from std, we can mix them in our code:

// For Apple targets and Linux 
#[cfg(any(apple_targets, target_os = "linux")]
fn foo() { }

[asomers]

Awesome @SteveLauC that looks perfect

[SteveLauC]

Friendly ping @lcruz99, would you like to do it in this PR:

1. Add that code snippet to build.rs
2. Replace #[cfg(any(target_os = "macos", target_os = "ios"))] with #[cfg(apple_targets)]

Please note that this would also make nix support watchos as well

---

If I do this, then this PR would be replaced by my PR, and I don't want to ruin your first contribution to nix :)

[lcruz99]

@SteveLauC will push those changes asap, thanks for the heads up :)

[lcruz99]

@SteveLauC @asomers FYI

Just pushed requested changes.

[SteveLauC]

Thanks! And congratulations on your first contribution to nix!