bug: wrap_comments mangles reference-style links

[domodwyer]

rustfmt with wrap_comments enabled is mangling reference-style intra-doc links by line wrapping them.

A comment like this:

/// Check out [my other struct] ([`Bananas`]) and [the method it has].
///
/// [my other struct]: a_long_name::b_long_name::c_long_name::d_long_name::e_long_name::f_long_name::Apples
/// [`Bananas`]: a_long_name::b_long_name::c_long_name::d_long_name::e_long_name::Bananas::fantastic()
/// [the method it has]: a_long_name::b_long_name::c_long_name::d_long_name::e_long_name::Bananas::fantastic()
pub struct A;

Is wrapped into:

/// Check out [my other struct] ([`Bananas`]) and [the method it has].
///
/// [my other struct]:
/// a_long_name::b_long_name::c_long_name::d_long_name::e_long_name::
/// f_long_name::Apples [`Bananas`]:
/// a_long_name::b_long_name::c_long_name::d_long_name::e_long_name::Bananas::
/// fantastic() [the method it has]:
/// a_long_name::b_long_name::c_long_name::d_long_name::e_long_name::Bananas::
/// fantastic()
pub struct A;

I would have expected rustfmt to leave the reference links alone, the wrapped comment makes cargo doc unhappy.

cargo doc output

doctest % cargo doc
 Documenting doctest v0.1.0 (/Users/dom/Desktop/doctest)
warning: unresolved link to `Bananas`
  --> src/lib.rs:20:36
   |
20 | /// Check out [my other struct] ([`Bananas`]) and [the method it has].
   |                                    ^^^^^^^ no item named `Bananas` in scope
   |
   = note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default
   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`

warning: unresolved link to `a_long_name::b_long_name::c_long_name::d_long_name::e_long_name::`
  --> src/lib.rs:23:5
   |
23 | /// a_long_name::b_long_name::c_long_name::d_long_name::e_long_name::
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no item named `` in module `e_long_name`

warning: unresolved link to `Bananas`
  --> src/lib.rs:24:27
   |
24 | /// f_long_name::Apples [`Bananas`]:
   |                           ^^^^^^^ no item named `Bananas` in scope
   |
   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`

warning: `doctest` (lib doc) generated 3 warnings

[ytmimi]

Thanks for submitting the issue and for working on the PR!