Merge pull request #822 from Silvertree2010/fix/h1632-slide-duplicate-appends-the-copy

Keep slide.duplicate copies next to their source in the section

crates/engine/src/cmd/slide.rs

@@ -218,6 +218,9 @@ fn duplicate(s: &mut Session, p: &Value) -> Result<Value> {
                 && let Some(sec) = doc.sections.get_mut(si)
             {
                 sec.slides.push(nid);
+                // Keep the section list in document order so the copy sits next to its source.
+                let order: Vec<SlideId> = doc.slides.iter().map(|x| x.id).collect();
+                sec.slides.sort_by_key(|x| order.iter().position(|o| o == x).unwrap_or(usize::MAX));
             }
         }
         sel.slide = (last + new_ids.len()).min(doc.slides.len().saturating_sub(1));
@@ -634,6 +637,23 @@ mod tests {
 
     use crate::Session;
 
+    #[test]
+    fn duplicate_keeps_section_order_in_step_with_slides() {
+        let mut s = Session::with_new();
+        while s.doc().expect("doc").doc.slides.len() < 3 {
+            s.execute("slide.new", &json!({})).expect("new slide");
+        }
+        s.execute("section.add", &json!({"at": 0})).expect("section");
+        let orig = s.doc().expect("doc").doc.slides.first().expect("slide").id;
+        s.execute("slide.duplicate", &json!({"index": 0})).expect("dup");
+        let st = s.doc().expect("doc");
+        let all: Vec<_> = st.doc.slides.iter().map(|x| x.id).collect();
+        let sec = &st.doc.sections.first().expect("section").slides;
+        assert_eq!(all.len(), 4);
+        assert_eq!(sec, &all, "section order must match slide order");
+        assert_eq!(sec.first(), Some(&orig));
+    }
+
     #[test]
     fn new_slide_body_leading_tabs_become_levels() {
         let mut s = Session::with_new();