warning: unresolved link to `long_cat`
  --> $DIR/macro-docs.rs:5:9
   |
LL |         /// A
   |         ^^^^^
...
LL | m!();
   | ---- in this macro invocation
   |
   = note: the link appears in this line:
           
           [`long_cat`] is really long
            ^^^^^^^^^^
   = note: no item named `long_cat` in scope
   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
   = note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default
   = note: this warning originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)

warning: 1 warning emitted