(Modules) Tracking issue for Picking a Module Path System variant

[Centril]

This is a sub-tracking issue for the RFC "Clarify and streamline paths and visibility" (rust-lang/rfcs#2126)
as well as the internals post Relative Paths in Rust 2018.

The issue deals with revamping paths and making a decision about whether we should pick:

• The uniform_paths variant.
  Proposed in Relative Paths in Rust 2018.
• The anchored_use_paths variant.
  You have to use self::, super::, and crate::, or an external crate name explicitly....
  See RFC: Clarify and streamline paths and visibility rfcs#2126).

• Implement all the things.
  • uniform_paths, #[feature(uniform_paths)]: allow use x::y; to resolve through self::x, not just ::x. #52923
  • anchored_use_paths
• Make both variants available to test in Edition Preview 2 with appropriate documentation on how to test.
• Adjust documentation (see instructions on forge)
• Pick a variant
• Stabilization PR (see instructions on forge)

Unresolved questions:

• Which variant do we pick?

[sanmai-NL]

Could you give more details about what has been implemented concretely, and what renaming operations are needed exactly? It comes down to: how can I start testing anything right now?

A priori, I vote for anchored_use_paths, for being the most explicit/teachable. One suggestion: I find the crate keyword a bit odd since it does not seem related to visibility at all. I suppose this has been debated before but it would be better if it becomes pubcrate or whatever.

[Centril]

cc @eddyb re. @sanmai-NL's question.

[eddyb]

@sanmai-NL Now that #52923 has landed, the next nightly should have both options available:

• anchored_use_paths has been the Rust 2018 default for some(?) time now
• uniform_paths you get by being on Rust 2018 and adding #![feature(uniform_paths)]

I'd suggesting trying the latter after upgrading to the edition, and report back if the ambiguity errors end up being too excessive.

AFAIK, the upgrade involves taking a Rust 2015 crate, adding #![feature(rust_2018_preview)] without changing the edition, running rustfix to apply the suggestions it gives for making same-crate paths explicit (i.e. prepending all paths that don't start with a crate name, with crate::), and only then do you switch the edition (usually in Cargo.toml) to Rust 2018.
You can remove #![feature(rust_2018_preview)] afterwards, since it's redundant.