engine: test ungrouping nested groups named out of order

Ungrouping a middle group, the group around it and then the innermost
group, all inside a fourth group, returns the four freed rectangles
once each, selects them, and leaves them in the fourth group in order.
Before the previous commit, the innermost group was listed twice and
replaced once, so the call also returned that group's id after the
group was gone.

crates/engine/src/tests.rs

@@ -959,6 +959,33 @@ fn ungrouping_a_nested_group_frees_its_shapes_into_the_outer_group() {
     }
 }
 
+/// Ungrouping nested groups in one call returns each freed shape once, whatever order the groups
+/// are named in. Before, a group freed into a group that the same call freed next was listed twice
+/// and replaced once, so the call returned the id of a group that no longer existed.
+#[test]
+fn ungrouping_nested_groups_in_any_order_returns_only_freed_shapes() {
+    fn rect(s: &mut Session, x: f64, y: f64) -> u64 {
+        s.execute("shape.insert", &json!({"preset": "rect", "rect": [x, y, 100, 100]})).unwrap()["id"].as_u64().unwrap()
+    }
+    fn group(s: &mut Session, ids: [u64; 2]) -> u64 {
+        s.execute("arrange.group", &json!({"ids": ids})).unwrap()["id"].as_u64().unwrap()
+    }
+    let sid = |id: u64| ShapeId(u32::try_from(id).unwrap());
+    let mut s = session();
+    s.execute("slide.new", &json!({"layout": "blank"})).unwrap();
+    let [a, b, c, d, e] = [(100.0, 100.0), (300.0, 100.0), (100.0, 300.0), (300.0, 300.0), (500.0, 300.0)].map(|(x, y)| rect(&mut s, x, y));
+    let inner = group(&mut s, [a, b]);
+    let middle = group(&mut s, [inner, c]);
+    let upper = group(&mut s, [middle, d]);
+    let outer = group(&mut s, [upper, e]);
+    let r = s.execute("arrange.ungroup", &json!({"ids": [middle, upper, inner]})).unwrap();
+    assert_eq!(r["ids"], json!([a, b, c, d]));
+    assert_eq!(s.doc().unwrap().selection.shapes, [sid(a), sid(b), sid(c), sid(d)]);
+    let st = s.doc().unwrap();
+    let order: Vec<ShapeId> = deckcraft_model::find_shape(st.shapes(), sid(outer)).unwrap().children().iter().map(|x| x.id).collect();
+    assert_eq!(order, [sid(a), sid(b), sid(c), sid(d), sid(e)]);
+}
+
 /// Grouping a group again and again stops at `MAX_GROUP_DEPTH`: past about 39 levels a saved
 /// .deckcraft file no longer opens, and past 64 commands such as format.languageAll miss the text.
 #[test]