Improve error messages for intra-doc links when there are backticks

[GuillaumeGomez]

In #87078, we arrived at the following situation:

error: incompatible link kind for `Foo::bar`
  --> $DIR/field-ice.rs:5:6
   |
LL | /// [`Foo::bar()`]
   |      ^^^^^^^^^^^^ help: to link to the field, remove the disambiguator: ``Foo::bar``

I want to underline this part in particular:

``Foo::bar``

Having two backticks is very weird. What I suggest instead is to reduce the "^^^^^" underlining part in order to not include backticks in it so then they can be removed from the error message as well, which would give:

error: incompatible link kind for `Foo::bar`
  --> $DIR/field-ice.rs:5:6
   |
LL | /// [`Foo::bar()`]
   |       ^^^^^^^^^^ help: to link to the field, remove the disambiguator: `Foo::bar`

I'll do it in the next days if no one does until then. :)

cc @jyn514

[estebank]

You can fix this by using a span_suggestion_verbose instead of span_suggestion:

rust/src/librustdoc/passes/collect_intra_doc_links.rs

Line 2110 in c49895d

diag.span_suggestion(sp, &help, msg, Applicability::MaybeIncorrect);

It'll take more vertical space, but it's ok.

---

If someone picks this up as their first contribution, you need to --bless the .stderr test files by running ./x.py test src/test/rustdoc-ui --stage 1 --bless from the root of the repo directory.

[b41sh]

@rustbot claim

[GuillaumeGomez]

@estebank It's a bit different here because we create the spans ourselves because they come from inside a doc comment. So I'm not sure if your suggestion will work out.

Also, in here it's src/test/rustdoc-ui, not src/test/ui (but otherwise it's the same). ;)

[estebank]

@GuillaumeGomez thanks for the correction!

As long as the span was synthesized correctly (including what side of a char the boundary falls on), then just changing the method will work as expected.

[GuillaumeGomez]

I had in mind to simply update the span instead in case the string was starting and ending with backticks.

[jyn514]

@GuillaumeGomez look at the code that's already there:

rust/src/librustdoc/passes/collect_intra_doc_links.rs

Lines 2104 to 2108 in c49895d

	let msg = if dox.bytes().nth(link_range.start) == Some(b'`') {
	format!("`{}`", suggestion.as_help(path_str))
	} else {
	suggestion.as_help(path_str)
	};

If you think this shouldn't use verbose, remove that instead. But I think it's better to show backticks if the user had them there originally.

[GuillaumeGomez]

We can take advantage of the span to exclude the backticks from the underlining, so then we can avoid displaying the backticks twice in the suggestion. As for the how, I guess it's fine as long as we get the output we want.