Prefer super or crate for internal module references

[tisonkun]

We can refer to modules in the same crate in different ways. For example, given a crate like this:

src/
  lib.rs
  a.rs
  b.rs

a can import trait B in b as crate::b::B or super::b::B. And if B is pub use in lib.rs, a can also refer B as crate::B. All these work, but it is troublesome to think about which way to go every time. So I think it will be better if we have a guideline about this.

My opinion is that we should prefer referring things relatively using super::b::B because:

• It doesn't assume if B is public or not
• When refactoring file structure, for example, if we want to move a.rs and b.rs to a sub-directory, the code still works

Originally posted by @huachaohuang in rust-lang/api-guidelines#255

[huachaohuang]

Thanks for moving it here. I am not that obsessed about this now. I think for internal usages, it is fine to choose any way that works.

[tisonkun]

@huachaohuang fine. If B is not public, the compiler will complain. For refactor purposes, the compiler will also help in spotting, and refactor tools will help.

I'll keep this issue open for a while to further comments if any.

[calebcartwright]

Thanks for reaching out but I'm going to close this as it's not really the type of thing we can codify in this guideline which is really geared to how the code the developer wrote should be styled/formatted (as opposed to analyzing the entirety of the crate to provide guidance on what the developer should have written.