Lint against `[T].iter().last()` and suggest `[T].last()`

[estebank]

Converting a slice into an iterator purely to get the last element of it is unnecessary, but if someone is not aware of [T]::last (like I was) would cargo cult the "turn into iterator and get the first/last element" pattern.

[scrabsha]

@rustbot claim

[compiler-errors]

This should almost certainly be a clippy lint instead.

[compiler-errors]

Specifically, #5597 implements a similar lint AFAICT.

[compiler-errors]

Am gonna transfer this:

@rustbot transfer clippy

[rustbot]

Failed to transfer issue:
error: Could not resolve to a Repository with the name 'rust-lang/clippy'.

[scrabsha]

Thanks for the pointers!

[compiler-errors]

@rustbot transfer rust-clippy

:3

[ada4a]

@rustbot label -P-low +A-lint

[estebank]

@compiler-errors keep in mind that clippy is in feature freeze until at least the end of the year, which includes introduction of new lints.