virtio-queue doctests fail due to build-time inclusion conditionals

[slp]

While building doctests, neither the test nor the doctest features are enabled. This means features gated behind [cfg(test...)] will not be available in doctests code. In virtio-queue case, this has an impact on mock visibility and some Descriptor helper methods aren't available either.

This is being discussed by the Rust Community here.

For the time being, we can either ignore the affected doctests (descriptor::Descriptor (line 21) and iterator::AvailIter (line 26)) or ungate those features. Personally, I'm fine with either.

[lauralt]

This doesn't seem to be a problem anymore if the tests are run with --all-features, i.e. cargo test --all-features, cargo test --doc --all-features. Do you think there's another option we should consider regarding running the tests?

[slp]

@lauralt Yes, the test-utils feature works around the issue if you pass --all-features or --features test-utils, but it fails with bare cargo test, which can both be confusing for final users and problematic when packaging the crate in a distro (this is how I've noticed the issue).

[lauralt]

It is indeed confusing, the same approach is used in event-manager as well, but it is documented. But besides the fact that it is confusing (there was a whole thread regarding this test feature proposal, but I fail to find it), we didn't think of having the bare cargo test passing as a requirement. Is this required for the distro use case, or is it possible to use --all-features or something else?

[slp]

I managed to work around this for Fedora, so I guess it should be possible to do the same thing for other distros. Should we just simply document this somewhere?

[lauralt]

Yes, I'll document it.

[lauralt]

@slp I opened #137, please have a look!

[slp]

@lauralt I see that #137 has already been merged. Thanks a lot for working on this!