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
The existing elided-lifetimes-in-paths lint (introduced in Nov. 2017's
accd997b5 / #46254) lacked stuctured suggestions and—much more
alarmingly—produced false positives on associated functions (like
`Ref::clone`) and on anonymous '_ lifetimes (!!—yes, the very
anonymous lifetimes that we meant to suggest "instead"). That this
went apparently unnoticed for so long maybe tells you something about
how many people actually bother to flip on allow-by-default lints.
After many hours of good old-fashioned American elbow grease—and a
little help from expert reviewers—it turns out that getting the right
answer is a lot easier if we fire the lint while lowering the Higher
Intermediate Representation.
The lint is promoted to the idioms-2018 group.
Also, in the matter of test filenames, "elided" only has one 'l' (see,
e.g., https://en.wiktionary.org/wiki/elide).
Resolves#52041.
- On mismatch between impl and trait method, point at the trait
signature.
- Point only at the method signature instead of the whole body on
trait/impl mismatch errors.
When refering to named lifetime conflict, point only at the method's
signature span instead of the entire method.
When the expected and found sup and sub traces are the same, avoid
redundant text.
