Promote waiting footnote definitions.

src/intermediate/registry.rs

@@ -60,6 +60,10 @@ pub(crate) async fn get_footnote_reference_id<'orig, 'parse>(
         return Ok(pos);
     }
 
+    if let Some(label) = label {
+        promote_footnote_definition(registry.clone(), label).await?;
+    }
+
     let existing_index = registry
         .lock()
         .unwrap()
@@ -147,3 +151,21 @@ async fn convert_definition_contents<'orig, 'parse>(
 
     Ok(contents)
 }
+
+/// Take a footnote definition that has not yet received a reference and move it into the active footnotes.
+pub(crate) async fn promote_footnote_definition<'orig, 'parse>(
+    registry: RefRegistry<'orig, 'parse>,
+    label: &'parse str,
+) -> Result<(), CustomError> {
+    let definition = {
+        let mut registry = registry.lock().unwrap();
+        let definition = registry.on_deck_footnote_ids.remove(label);
+        definition
+    };
+    if let Some(elements) = definition {
+        let contents = convert_definition_contents(registry.clone(), elements).await?;
+        let mut registry = registry.lock().unwrap();
+        registry.footnote_ids.push((Some(label), contents));
+    }
+    Ok(())
+}