Fix build at nightly

[giraffate]

changelog: none

The build fails when using the following version of nightly. The error message is the same as https://github.com/rust-lang/rust-clippy/pull/5773/checks?check_run_id=845930061 .

$ rustc -V
rustc 1.46.0-nightly (8ac1525e0 2020-07-07)

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @matthiaskrgr (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[flip1995]

Thanks for notifying us! We have a process for when this happens, described here: https://github.com/rust-lang/rust-clippy/blob/master/CONTRIBUTING.md#fixing-build-failures-caused-by-rust

I'll get right to it, so that it builds with the latest rustc master again ASAP.

[flip1995]

cc #5776

[giraffate]

@flip1995 Oh, I was overlooking it. Thanks for your information!
I have a question, can I do this process? Or should I inform you maintainers?

[flip1995]

You can do this process. But be aware that you will hit some difficulties, since the git-subtree command shipped with git cannot be used for that, but has to be replaced by a fixed version from a PR to git.

The documentation should include every step you have to take to get it working though. If you're not able to get it to work, let me know, so that we can improve the documentation. (either via ping on github or on discord, also @flip1995)

[giraffate]

I understood. Thanks for teaching me!