One of the challenges with rustc is that the RLS can't handle it, since it's a
bootstrapping compiler. This makes code navigation difficult. One solution is to
ctags has a long history and several variants. Exuberant Ctags seems to be
quite commonly distributed but it does not have out-of-box Rust support. Some
distributions seem to use Universal Ctags, which is a maintained fork
and does have built-in Rust support.
The following script can be used to set up Exuberant Ctags: https://github.com/nikomatsakis/rust-etags.
ctags integrates into emacs and vim quite easily. The following can then be
used to build and generate tags:
$ rust-ctags src/lib* && ./x.py build <something>
This allows you to do "jump-to-def" with whatever functions were around when you last built, which is ridiculously useful.