Added Linux aarch64 capability

[K0HAX]

I have a Pinebook Pro and I wanted to be able to use Element Desktop on it.

This solution is working at the time of writing with Element Desktop 1.10.3.

I added build:aarch64 to package.json.
electron-builder tries to use its bundled x86 version of fpm by default, so the aarch64 builder uses the environment variable USE_SYSTEM_FPM=true to override this.

I added the aarch64-unknown-linux-gnu target to scripts/hak/target.ts

After making those changes, in Gentoo I ran:

sudo gem install fpm
sudo ln -s /usr/local/lib64/ruby/gems/2.7.0/bin/fpm /usr/local/bin/
yarn install
yarn run fetch --importkey
yarn run fetch --noverify --cfgdir ""
yarn run build:native --target aarch64-unknown-linux-gnu
yarn run build:aarch64

I didn't find an fpm package in Gentoo's package manager, so I did it a lazy way. I'm sure there's a more elegant way to handle that part.

---

Here's what your changelog entry will look like:

✨ Features

• Added Linux aarch64 capability (#323). Contributed by @K0HAX.

[novocaine]

Is there a way to make this "just work" if you run yarn run build:native on aarch64 as it does on other platforms?

[K0HAX]

I just tested with yarn run build:native on aarch64 and that does "just work".
Unfortunately, yarn run build does not "just work" because electron-builder is pulling and trying to use fpm-1.9.3-2.3.1-linux-x86.7z, which doesn't work on ARM processors. That's what USE_SYSTEM_FPM=true fixes. That seems to be a bug in electron-builder, but their issue history suggests to me that they aren't interested in fixing that bug.

I don't know enough about how package.json works to fix this.

[novocaine]

Okay! I think we just might need to make a note of how to get this to work in https://github.com/vector-im/element-desktop/blob/develop/docs/native-node-modules.md#compiling-for-specific-architectures ?

Also, I wonder .. if the workaround means that there's always a likely extra step to install a custom FPM locally, maybe the docs should suggest passing USE_SYSTEM_FPM as an explicit environment variable when running yarn run build (rather than embedding it in the build script).. This might be a bit more transparent to people and allow them to figure out their own workaround if needed.

[turt2live]

the change looks fine as-is, though I do agree with @novocaine here in that documentation is the way to go on this.

For a project like this, the README is more important than build commands magically working ;)

[t3chguy]

#376 adds the target already

[t3chguy]

Agreed with the others on this issue, that the env var should be a documentation feature rather than a built-in command. If you want to open a new PR to document how to build aarch64 using the existing commands & targets that'd be ideal, thanks!