idiom lints for removing `extern crate`
Based off of https://github.com/rust-lang/rust/pull/49789
This contains two lints:
- One that suggests replacing pub extern crates with pub use, and removing non-pub extern crates entirely
- One that suggests rewriting `use modulename::...::cratename::foo` as `cratename::foo`
The latter is a bit tricky to emit suggestions for; for one this involves splicing spans (never a good idea), and it also won't be able to correctly
handle `use module::{cratename, foo}` and use-trees. I'm not sure how to proceed here. Currently it doesn't suggest anything at all.
Perhaps we can go the other way and suggest removal of all extern crates _except_ those used through modules (stash node ids somewhere) and suggest replacing those with `<visibility> use`?
r? @nikomatsakis
fixes https://github.com/rust-lang/rust/issues/48719
0da1a69003