Cargo hangs with 100% CPU usage

[MagaTailor]

Trying to cargo build https://github.com/swiboe/swiboe prints:

 Updating registry `https://github.com/rust-lang/crates.io-index`
    Updating git repository `https://github.com/carllerche/mio.git`
    Updating git repository `https://github.com/carllerche/nix-rust`
    Updating git repository `https://github.com/alexcrichton/wio`
    Updating git repository `https://github.com/carllerche/bytes`

and then after more than 10 minutes (arm) of cargo using 100% cycles:

failed to select a version for `libc` (required by `rand`):
all possible versions conflict with previously selected versions of `libc`
  version 0.1.0 in use by libc v0.1.0
  possible versions to select: 0.1.12, 0.1.10, 0.1.8, 0.1.7, 0.1.6, 0.1.5, 0.1.4, 0.1.3, 0.1.2, 0.1.1

After modifying Cargo.toml to use newer libc it seems to just hang, but using the cargo-bake command suddenly printed this:

no matching package named `wio` found (required by `mio`)
location searched: https://github.com/alexcrichton/wio
version required: *

It doesn't reproduce since then. Nice non-determinism!

[alexcrichton]

I think that this is a dupe of #2090, so closing in favor of that, but thanks for the report!

[MagaTailor]

Using -j 1 shows it hangs doing exactly this:

Updating git repository `https://github.com/alexcrichton/wio`

The swiboe repo is abandoned at the moment so maybe this dependency shouldn't even be there?

[alexcrichton]

The -j flag doesn't affect the resolution step, and it's likely not hanging on actually updating the git repo, that was just the last error message printed. It's likely stuck in resolve and not making progress nearly as quickly as it should be.