add structured suggestions and fix false-positive for elided-lifetimes-in-paths lint
This adds structured suggestions to the elided-lifetimes-in-paths lint (introduced in Nov. 2017's #46254), prevents it from emitting a false-positive on anonymous (underscore) lifetimes (!), and adds it to the idioms-2018 group (#52041).
~~As an aside, "elided-lifetimes-in-paths" seems like an unfortunate name, because it's not clear exactly what "elided" means. The motivation for this lint (see original issue #45992, and [RFC 2115](e978a8d301/text/2115-argument-lifetimes.md (motivation))) seems to be specifically about not supplying angle-bracketed lifetime arguments to non-`&` types, but (1) the phrase "lifetime elision" has historically also referred to the ability to not supply a lifetime name to `&` references, and (2) an `is_elided` method in the HIR returns true for anoymous/underscore lifetimes, which is _not_ what we're trying to lint here. (That naming confusion is almost certainly what led to the false positive addressed here.) Given that the lint is relatively new and is allow-by-default, is it too late to rename it ... um, _again_ (#50879)?~~
~~This does _not_ address a couple of other false positives discovered in https://github.com/rust-lang/rust/issues/52041#issuecomment-402547901.~~
r? @nikomatsakis
cc @nrc @petrochenkov
ffaf3d2567
