Avoid downloading multiple resolvers

[illicitonion]

Instead, download just the one that's needed for the host platform.

Fixes #693

[UebelAndre]

Does this mean each crate_universe repository will download it's own binary? I think this is a step forward but it might be worth having a second repository rule for downloading the resolver and have crate_universe proper depend on that.

I feel like this would be a pretty quick change, it's just moving the downloading logic into it's own rule. Your thoughts?

[illicitonion]

Does this mean each crate_universe repository will download it's own binary?

Ish - if you set the sha256, bazel should deduplicate the downloads. If you don't, it will probably perform multiple downloads.

it might be worth having a second repository rule for downloading the resolver and have crate_universe proper depend on that.

I feel like this would be a pretty quick change, it's just moving the downloading logic into it's own rule. Your thoughts?

I'd rather not invent a separate "avoid downloading the same file multiple times" mechanism, given the sha256 deduping is designed for that, but can add one if you think it'd be a big problem.

[UebelAndre]

Ish - if you set the sha256, bazel should deduplicate the downloads. If you don't, it will probably perform multiple downloads.

If Bazel will use a cached binary based on the sha256 value then that works for me 😄

I'd rather not invent a separate "avoid downloading the same file multiple times" mechanism, given the sha256 deduping is designed for that, but can add one if you think it'd be a big problem.

No, if there's an existing mechanism for doing this that's all I care about.

[UebelAndre]

Oh crap, this broke bootstrapping. Totally didn't think about that 😞

Can you add a followup PR to update the bootstrap script so users can easily iterate on changes?

[UebelAndre]

I opened #697 to track the over all plan for CI, but I had setup the bootstrapping to initially solve for this. I wanted to open a PR which runs the bootstrapping script as a shell_command when building examples/crate_universe which would have run as it's own job. Maybe that's a bad idea? We should continue this conversation on the issue I opened or some other one if we want to be more granular.