Fix footnote-reference numbering (#4456)

crates/typst/src/model/footnote.rs

@@ -93,6 +93,15 @@ impl FootnoteElem {
         Self::new(FootnoteBody::Reference(label))
     }
 
+    /// Creates a new footnote referencing the footnote with the specified label,
+    /// with the other fields from the current footnote cloned.
+    pub fn into_ref(&self, label: Label) -> Self {
+        Self {
+            body: FootnoteBody::Reference(label),
+            ..self.clone()
+        }
+    }
+
     /// Tests if this footnote is a reference to another footnote.
     pub fn is_ref(&self) -> bool {
         matches!(self.body(), FootnoteBody::Reference(_))

crates/typst/src/model/reference.rs

@@ -177,8 +177,8 @@ impl Show for Packed<RefElem> {
 
         let elem = elem.at(span)?;
 
-        if elem.func() == FootnoteElem::elem() {
-            return Ok(FootnoteElem::with_label(target).pack().spanned(span));
+        if let Some(footnote) = elem.to_packed::<FootnoteElem>() {
+            return Ok(footnote.into_ref(target).pack().spanned(span));
         }
 
         let elem = elem.clone();

tests/suite/model/footnote.typ

@@ -187,3 +187,7 @@ B #footnote[b]
 #set page(height: 50pt)
 #footnote[A]
 #footnote[B]
+
+--- issue-4454-footnote-ref-numbering ---
+// Test that footnote references are numbered correctly.
+A #footnote(numbering: "*")[B]<fn>, C @fn, D @fn, E @fn.