Multiple unused formatting argument notes should use multispan

[brson]

After #37613, the output for format! errors looks like:

error: multiple unused formatting arguments
  --> $DIR/format-foreign.rs:12:5
   |
12 |     println!("%.*3$s %s!/n", "Hello,", "World", 4);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: argument never used
  --> $DIR/format-foreign.rs:12:30
   |
12 |     println!("%.*3$s %s!/n", "Hello,", "World", 4);
   |                              ^^^^^^^^
note: argument never used
  --> $DIR/format-foreign.rs:12:40
   |
12 |     println!("%.*3$s %s!/n", "Hello,", "World", 4);
   |                                        ^^^^^^^
note: argument never used
  --> $DIR/format-foreign.rs:12:49
   |
12 |     println!("%.*3$s %s!/n", "Hello,", "World", 4);
   |                                                 ^
   = help: `%.*3$s` should be written as `{:.2$}`
   = help: `%s` should be written as `{}`
   = note: printf formatting not supported; see the documentation for `std::fmt`
= note: this error originates in a macro outside of the current crate

that's a lot of lines dedicated to underlining macro acruments. They should all be output in one multispan.

cc @DanielKeep @estebank @jonathandturner @GuillaumeGomez

[GuillaumeGomez]

Hum indeed. If no one has taken it in 12 hours, I'll give it a look.

[DanielKeep]

@GuillaumeGomez I'm poking at it right now. I think I need to fix ExtCtxt's methods to accept <S: Into<MultiSpan>> instead of just Span, and then I can use MultiSpan directly.

After all, I created the problem, I should probably fix it. :P

[GuillaumeGomez]

Perfect. Good luck! :)

[cramertj]

I believe this should be closed.

[GuillaumeGomez]

Hold on, it seems the PR is still open.