Restart Numbering keeps the list's own level definitions (#1351) (#1409)

crates/doc/src/numbering.rs

@@ -240,10 +240,14 @@ impl Numbering {
     }
     /// A new `num` that restarts numbering of an existing list.
     pub fn restart(&mut self, num: u32) -> Option<u32> {
-        let a = self.num(num)?.abstract_id;
+        let source = self.num(num)?;
+        let a = source.abstract_id;
+        let level_overrides = source.level_overrides.clone();
         let nid = self.nums.iter().map(|n| n.id + 1).max().unwrap_or(1).max(1);
-        let starts = self.abstracts.iter().find(|x| x.id == a).map(|x| x.levels.iter().enumerate().map(|(i, l)| (i as u8, l.start)).collect());
-        self.nums.push(Num { id: nid, abstract_id: a, start_overrides: starts.unwrap_or_default(), ..Default::default() });
+        // Every level starts again at its own effective start, so a level this list defines itself keeps its start.
+        let levels = self.abstracts.iter().find(|x| x.id == a).map_or(0, |x| x.levels.len());
+        let start_overrides = (0..levels).filter_map(|i| self.level(num, i as u8).map(|l| (i as u8, l.start))).collect();
+        self.nums.push(Num { id: nid, abstract_id: a, start_overrides, level_overrides });
         Some(nid)
     }
     /// Find an existing list whose first level matches `kind`, so consecutive bullet clicks reuse it.
@@ -449,4 +453,19 @@ mod tests {
         assert_eq!(c.next_label(&n, b, 0).unwrap().0, "•");
         assert_eq!(n.find_kind(ListKind::Bullet), Some(b));
     }
+
+    #[test]
+    fn restart_keeps_the_list_s_own_level_definitions() {
+        let mut n = Numbering::default();
+        let id = n.add_list(ListKind::Numbered);
+        let own = Level { format: NumFormat::UpperRoman, text: "Part %1".into(), indent: 90.0, hanging: 40.0, start: 5, ..Level::default() };
+        if let Some(num) = n.nums.iter_mut().find(|x| x.id == id) {
+            num.level_overrides.push((0, own.clone()));
+        }
+        let r = n.restart(id).unwrap();
+        assert_eq!(n.num(r).unwrap().level_overrides, vec![(0, own.clone())]);
+        assert_eq!(n.level(r, 0), Some(&own));
+        let mut c = Counters::default();
+        assert_eq!(c.next_label(&n, r, 0).unwrap().0, "Part V");
+    }
 }