test(blend): pin symmetric spine handles and invalid conversion inputs (#2544)

crates/engine/src/tests_blendspine.rs

@@ -66,6 +66,57 @@ fn a_spine_point_added_and_moved_bends_the_blend() {
     assert!(center(&steps(&s, g)[1]).distance(Point::new(55.0, 5.0)) < 1e-6);
 }
 
+/// #2544: an Anchor Point drag on a blend spine must create two symmetric
+/// handles, not bend the adjacent segment and leave one handle behind.
+#[test]
+fn spine_anchor_conversion_preserves_keys_and_undo() {
+    let mut s = session();
+    let (a, b, g) = blend(&mut s);
+    s.execute("object.blend.spine.addAnchor", &json!({"id": g.0, "x": 55, "y": 5})).unwrap();
+    let keys_before = spec(&s, g).key_anchors;
+    s.execute(
+        "object.blend.spine.convertAnchor",
+        &json!({"id": g.0, "anchor": 1, "to": "smooth", "x": 55, "y": 35}),
+    )
+    .unwrap();
+    let sp = spec(&s, g);
+    assert_eq!(sp.key_anchors, keys_before);
+    let middle = sp.spine.as_ref().unwrap().subpaths[0].anchors[1];
+    assert_eq!(middle.kind, vectorcraft_geom::AnchorKind::Smooth);
+    assert_eq!(middle.p, Point::new(55.0, 5.0));
+    assert_eq!(middle.h_in, Point::new(55.0, -25.0));
+    assert_eq!(middle.h_out, Point::new(55.0, 35.0));
+    assert_eq!(center(&node(&s, a)), Point::new(5.0, 5.0));
+    assert_eq!(center(&node(&s, b)), Point::new(105.0, 5.0));
+
+    s.execute("edit.undo", &json!({})).unwrap();
+    let before = spec(&s, g);
+    assert_eq!(before.spine.unwrap().subpaths[0].anchors[1].h_out, Point::new(55.0, 5.0));
+    s.execute("edit.redo", &json!({})).unwrap();
+    assert_eq!(spec(&s, g).spine.unwrap().subpaths[0].anchors[1], middle);
+
+    s.execute("object.blend.spine.convertAnchor", &json!({"id": g.0, "anchor": 1, "to": "corner"})).unwrap();
+    let corner = spec(&s, g).spine.unwrap().subpaths[0].anchors[1];
+    assert!(!corner.has_in() && !corner.has_out());
+    assert_eq!(corner.kind, vectorcraft_geom::AnchorKind::Corner);
+}
+
+#[test]
+fn spine_conversion_rejects_invalid_arguments_without_mutation() {
+    let mut s = session();
+    let (_, _, g) = blend(&mut s);
+    let before = spec(&s, g);
+    for params in [
+        json!({"id": g.0, "anchor": 5, "to": "smooth", "x": 20, "y": 20}),
+        json!({"id": g.0, "anchor": 0, "to": "unknown"}),
+        json!({"id": g.0, "anchor": 0, "to": "smooth", "x": 10}),
+        json!({"id": g.0, "anchor": 0, "to": "smooth", "x": f64::MAX, "y": 1}),
+    ] {
+        assert!(s.execute("object.blend.spine.convertAnchor", &params).is_err(), "{params}");
+        assert_eq!(spec(&s, g), before);
+    }
+}
+
 #[test]
 fn moving_a_key_point_moves_the_key_and_the_other_way_round() {
     let mut s = session();