Naming of fat binaries for M1 (Apple silicon)

[vweevers]

In order to support M1 (Apple silicon), addon authors can build so-called fat binaries, that work on both x86_64 and arm64. This seems like the easiest way to add M1 support. For example fsevents/fsevents#350.

It's at odds with our current folder structure though. What would the arch be in e.g. darwin-<arch>/node.napi.node?

[vweevers]

Options:

1. Dual arch: darwin-x64_arm64/*.node. It'll be up to the addon author to setup their CI to produce this folder name.
2. Some special name like darwin-universal/*.node.
3. Same as today: darwin-x64/*.node. As a temporary solution, node-gyp-build could attempt to load this prebuild if os.arch() === 'arm64'. If it succeeds it must mean the prebuild is a fat binary.

[mafintosh]

@vweevers would copying it work? it's zipped anyway.

[vweevers]

I didn't try producing a fat binary yet but I assume it will be bigger than a single-arch binary (which on rocksdb for example is already 1.81 MB gzipped). So I would prefer not duplicating it.

[lpinca]

I'm fine with option 1.

[mafintosh]

yea 1) or 2) is fine with me as well.

[chenrui333]

I think option 1 is better.

[vweevers]

Let's go for option 1 then.

I wrote that "It'll be up to the addon author to setup their CI to produce this folder name" but perhaps prebuildify can do it.

Somewhat tricky because although we currently take a custom --arch or PREBUILD_ARCH which affects the folder name, we would also forward that value to node-gyp (and thus gyp and thus binding.gyp) which will probably not like the value x64_arm64.

In addition, we do that forwarding via node-gyp --target-arch:

prebuildify/index.js

Line 190 in 4f71944

args.push('--target_arch=' + opts.arch)

Which I think is no longer supported in node-gyp (according to docs and a quick look at code). We should be passing --arch instead.

On the other hand, if I'm right that --target-arch is ignored (since which version?) then we can avoid this problem for now. AFAICT node-gyp has no builtin support for fat binaries anyway; addon authors have to specify -arch x86_64 -arch arm64 compiler flags in their binding.gyp.

[vweevers]

I checked, --target-arch does still work to some extent, thanks to this, but we're missing out on earlier logic that's based on --arch (for example here and here).

The node-gyp --arch option is documented since [email protected] (nodejs/node-gyp@4ee3132) which is old enough (node 8.6.0 bundles [email protected], fx).

So I propose we replace --target-arch with --arch. Using arch.split('+')[0] as the value (note that in prebuild/node-gyp-build#40 we decided to use + as arch separator instead of _) so that we only pass the first arch to node-gyp. I will send a PR.

[vweevers]

Done in node-gyp-build 4.3.0 and prebuildify 4.2.1.