Compose: cross-reference index no longer rebuilds itself (#851)

The cross-reference index composed its destination stories through
the cache. One with a running header asked for the running-header
index, which composed the story holding the cross-reference, which
asked for the cross-reference index again: the stack overflowed and
the app aborted. Destination stories with a running header are now
composed without it, like those with cross-references already were.

crates/compose/src/xref.rs

@@ -19,15 +19,17 @@ pub fn has_xrefs(st: &Story) -> bool {
 }
 
 impl XrefIndex {
-    /// `get` composes a story (normally through the cache). Stories that themselves hold
-    /// cross-references are composed without resolving them (their anchors' pages hardly move).
+    /// `get` composes a story (normally through the cache). Stories that hold cross-references or
+    /// running headers are composed without resolving them (their anchors' pages hardly move):
+    /// through the cache they would build this index again, directly or by way of the running-header index.
     pub fn build(doc: &Document, get: &dyn Fn(StoryId) -> Arc<ComposedStory>) -> XrefIndex {
         let mut pages = HashMap::new();
         for (sid, st) in &doc.stories {
             if st.anchors.is_empty() {
                 continue;
             }
-            let cs = if has_xrefs(st) { Arc::new(crate::compose_story(doc, *sid, &Default::default())) } else { get(*sid) };
+            let indexed = has_xrefs(st) || crate::vars::has_running(doc, st);
+            let cs = if indexed { Arc::new(crate::compose_story(doc, *sid, &Default::default())) } else { get(*sid) };
             for a in &st.anchors {
                 let Some(pos) = st.anchor_pos(a.id) else { continue };
                 if let Some((page, ..)) = crate::vars::place(doc, &cs, pos) {

crates/engine/src/cmd/xref.rs

@@ -214,4 +214,23 @@ mod tests {
         s.execute("edit.undo", &json!({})).unwrap();
         assert_eq!(s.execute("xref.list", &json!({})).unwrap()[0]["text"], "(p. 3)");
     }
+
+    #[test]
+    fn cross_reference_into_a_story_with_a_running_header_composes() {
+        let mut s = Session::new();
+        s.execute("file.new", &json!({"pages": 1, "facingPages": false})).unwrap();
+        let head = s.execute("frame.create", &json!({"rect": [72, 72, 400, 120], "content": "text", "text": "Chapter"})).unwrap()["story"].clone();
+        let body = s.execute("frame.create", &json!({"rect": [72, 200, 400, 300], "content": "text", "text": "See"})).unwrap()["story"].clone();
+        s.execute("text.select", &json!({"story": head, "anchor": 0, "focus": 0})).unwrap();
+        s.execute("variables.insert", &json!({"name": "Running Header"})).unwrap();
+        s.execute("text.select", &json!({"story": body, "anchor": 3, "focus": 3})).unwrap();
+        s.execute("xref.insert", &json!({"story": head, "para": 0})).unwrap();
+        // The cross-reference index and the running-header index used to build each other without end.
+        assert_eq!(s.execute("xref.list", &json!({})).unwrap()[0]["text"], "\u{201C}Chapter\u{201D} on page 1");
+        // The header shows the body's paragraph in front of its own text.
+        let d = s.doc().unwrap().doc.clone();
+        let cs = s.cache.get(&d, StoryId(head.as_u64().unwrap()), None);
+        let glyphs: usize = cs.frames[0].lines.iter().map(|l| l.glyphs.iter().filter(|g| g.visible && g.adv > 0.0).count()).sum();
+        assert_eq!(glyphs, "SeeChapter".len());
+    }
 }