Implementation: #7649
Original proposal: #6699
Documentation: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#config-include
Issues: Z-config-include Nightly: `include` config key

Summary

Adds the include config key to include other config files.

Unresolved issues

• Should there be any restriction on the filename? Currently there isn't. I was initially considering restricting to .cargo/config-* in case we want to safely use other filenames in .cargo/ for other purposes. However, it seems like an unnatural restriction. Another restriction is that it should maybe end in .toml?

FCP