In RustCrypto/hashes xargo is used in CI to verify if all crates are indeed no_std. But with the addition of std feature (see branch digest_v0.8) which per convention is enabled by default, xargo does not work correctly anymore. I've changed CI config to use the following command on workspace (Travis build):

xargo build --all --no-default-features --verbose --target armv7-unknown-linux-gnueabihf

But it fails with this error:

error[E0463]: can't find crate for `std`
  |
  = note: the `armv7-unknown-linux-gnueabihf` target may not be installed

For some reason it builds digest crate (on which all crates in the workspace are dependent) with enabled std feature. If I'll change directory to e.g. md2 and will execute the same command it will finish without any problems. It returns the same error even if md2 is a single crate in the workspace, so it does not look like std feature have slipped somewhere. So my guess is that for some reason xargo does not propagate --no-default-features when it builds all crates in workspace.