[rustdoc] Fix handling of footnote reference in footnote definition

src/librustdoc/html/markdown/footnotes.rs

@@ -1,7 +1,7 @@
 //! Markdown footnote handling.
 use std::fmt::Write as _;
 
-use pulldown_cmark::{Event, Tag, TagEnd, html};
+use pulldown_cmark::{CowStr, Event, Tag, TagEnd, html};
 use rustc_data_structures::fx::FxIndexMap;
 
 use super::SpannedEvent;
@@ -21,7 +21,7 @@ struct FootnoteDef<'a> {
     id: usize,
 }
 
-impl<'a, 'b, I> Footnotes<'a, 'b, I> {
+impl<'a, 'b, I: Iterator<Item = SpannedEvent<'a>>> Footnotes<'a, 'b, I> {
     pub(super) fn new(iter: I, existing_footnotes: &'b mut usize) -> Self {
         Footnotes { inner: iter, footnotes: FxIndexMap::default(), existing_footnotes }
     }
@@ -34,31 +34,50 @@ impl<'a, 'b, I> Footnotes<'a, 'b, I> {
         // Don't allow changing the ID of existing entrys, but allow changing the contents.
         (content, *id)
     }
+
+    fn handle_footnote_reference(&mut self, reference: &CowStr<'a>) -> Event<'a> {
+        // When we see a reference (to a footnote we may not know) the definition of,
+        // reserve a number for it, and emit a link to that number.
+        let (_, id) = self.get_entry(reference);
+        let reference = format!(
+            "<sup id=\"fnref{0}\"><a href=\"#fn{0}\">{1}</a></sup>",
+            id,
+            // Although the ID count is for the whole page, the footnote reference
+            // are local to the item so we make this ID "local" when displayed.
+            id - *self.existing_footnotes
+        );
+        Event::Html(reference.into())
+    }
+
+    fn collect_footnote_def(&mut self) -> Vec<Event<'a>> {
+        let mut content = Vec::new();
+        while let Some((event, _)) = self.inner.next() {
+            match event {
+                Event::End(TagEnd::FootnoteDefinition) => break,
+                Event::FootnoteReference(ref reference) => {
+                    content.push(self.handle_footnote_reference(reference));
+                }
+                event => content.push(event),
+            }
+        }
+        content
+    }
 }
 
 impl<'a, 'b, I: Iterator<Item = SpannedEvent<'a>>> Iterator for Footnotes<'a, 'b, I> {
     type Item = SpannedEvent<'a>;
 
     fn next(&mut self) -> Option<Self::Item> {
         loop {
-            match self.inner.next() {
+            let next = self.inner.next();
+            match next {
                 Some((Event::FootnoteReference(ref reference), range)) => {
-                    // When we see a reference (to a footnote we may not know) the definition of,
-                    // reserve a number for it, and emit a link to that number.
-                    let (_, id) = self.get_entry(reference);
-                    let reference = format!(
-                        "<sup id=\"fnref{0}\"><a href=\"#fn{0}\">{1}</a></sup>",
-                        id,
-                        // Although the ID count is for the whole page, the footnote reference
-                        // are local to the item so we make this ID "local" when displayed.
-                        id - *self.existing_footnotes
-                    );
-                    return Some((Event::Html(reference.into()), range));
+                    return Some((self.handle_footnote_reference(reference), range));
                 }
                 Some((Event::Start(Tag::FootnoteDefinition(def)), _)) => {
                     // When we see a footnote definition, collect the assocated content, and store
                     // that for rendering later.
-                    let content = collect_footnote_def(&mut self.inner);
+                    let content = self.collect_footnote_def();
                     let (entry_content, _) = self.get_entry(&def);
                     *entry_content = content;
                 }
@@ -80,17 +99,6 @@ impl<'a, 'b, I: Iterator<Item = SpannedEvent<'a>>> Iterator for Footnotes<'a, 'b
     }
 }
 
-fn collect_footnote_def<'a>(events: impl Iterator<Item = SpannedEvent<'a>>) -> Vec<Event<'a>> {
-    let mut content = Vec::new();
-    for (event, _) in events {
-        if let Event::End(TagEnd::FootnoteDefinition) = event {
-            break;
-        }
-        content.push(event);
-    }
-    content
-}
-
 fn render_footnotes_defs(mut footnotes: Vec<FootnoteDef<'_>>) -> String {
     let mut ret = String::from("<div class=\"footnotes\"><hr><ol>");
 

tests/rustdoc/footnote-reference-in-footnote-def.rs

@@ -0,0 +1,20 @@
+// Checks that footnote references in footnote definitions are correctly generated.
+// Regression test for <https://github.com/rust-lang/rust/issues/131946>.
+
+#![crate_name = "foo"]
+
+//@ has 'foo/index.html'
+//@ has - '//*[@class="docblock"]/p/sup[@id="fnref1"]/a[@href="#fn1"]' '1'
+//@ has - '//li[@id="fn1"]/p' 'meow'
+//@ has - '//li[@id="fn1"]/p/sup[@id="fnref2"]/a[@href="#fn2"]' '2'
+//@ has - '//li[@id="fn1"]//a[@href="#fn2"]' '2'
+//@ has - '//li[@id="fn2"]/p' 'uwu'
+//@ has - '//li[@id="fn2"]/p/sup[@id="fnref1"]/a[@href="#fn1"]' '1'
+//@ has - '//li[@id="fn2"]//a[@href="#fn1"]' '1'
+
+//! # footnote-hell
+//!
+//! Hello [^a].
+//!
+//! [^a]: meow [^b]
+//! [^b]: uwu [^a]