when suggesting to remove a crate, we leave a blank line

[nikomatsakis]

As of #51015, the rustfix result for:

#![warn(unused_crates)]
extern crate foo;
fn main() { }

is

#![warn(unused_crates)]

fn main() { }

but not

#![warn(unused_crates)]
fn main() { }

[nikomatsakis]

Probably the easiest way to fix this is to extend the replacement span by one character if the character after it is \n, somewhere around here:

https://github.com/nikomatsakis/rust/blob/7b7901bf710085a601eed58bf26efb571fe5d25b/src/librustc_typeck/check_unused.rs#L174

[nikomatsakis]

Partial diffs here (doesn't work): https://gist.github.com/nikomatsakis/7351f61938624c8e5a9921bbef63add3

One complication: extending to trailing newlines is not enough, we want to be sure that extern is at the start of the line too! i.e., this test:

#![warn(unused_crates)]
/* bar! */ extern crate foo;
fn main() { }

should probably result in

#![warn(unused_crates)]
/* bar! */ 
fn main() { }

not

#![warn(unused_crates)]
/* bar! */ fn main() { }

(Plausibly, though, we might kill trailing whitespace? How much do we care anyway... maybe rustfix wants to do this?)

[rylev]

Triage: this is still an issue. Here's the code updated code considering the lint changed since this issues was filed:

#![warn(unused_extern_crates)]
extern crate foo;
fn main() {}