Rustdoc looks in different namespaces for diagnostics: https://github.com/rust-lang/rust/blob/66a9cfadf89439ad3ea1b67b996c0a90ca4763bf/src/librustdoc/passes/collect_intra_doc_links.rs#L1569-L1572
So this is handled properly:

warning: unresolved link to `file::into_iter`
 --> tmp.rs:1:6
  |
1 | /// [type@file::into_iter]
  |      ^^^^^^^^^^^^^^^^^^^^ `file` is a macro, not a module or type, and cannot have associated items

However (after #76955), resolution_failure only looks at other namespaces if there are multiple path segments. So https://github.com/rust-lang/rust/blob/66a9cfadf89439ad3ea1b67b996c0a90ca4763bf/src/librustdoc/passes/collect_intra_doc_links.rs#L1114 and https://github.com/rust-lang/rust/blob/66a9cfadf89439ad3ea1b67b996c0a90ca4763bf/src/librustdoc/passes/collect_intra_doc_links.rs#L1242-L1244 are still necessary, because they handle cases like value@file and type@file.

It would be nice to clean this up so that WrongNamespace is only handled in one place, in resolution_failure.

Originally posted by @jyn514 in #76955 (comment)