rustdoc: recursive footnote not rendered correctly

[Noratrieb]

rustdoc footnote-hell.md

# footnote-hell

Hello [^a].

[^a]: meow [^b]
[^b]: uwu [^a]

I expected to see this happen: all the links are correct, the backlinks are at least not completely wrong

Instead, this happened: a mess

• The first 1 points to #fn1
• The second 1 points to #b
• The third 1 points to #a

The backlinks are #fnref1 and #fnref2 respectively, which seems correct.

Meta

rustc --version --verbose:

rustdoc 1.84.0-nightly (3ed6e3cc6 2024-10-17)

[GuillaumeGomez]

That was a funny case. So the fix is simple: we need to check for footnote references in footnote definitions. I have a fix ready, sending the patch once I added tests.