Isolation mode: double-clicking a single object isolates it

With Double Click To Isolate on, the Selection tool isolated groups only. A
double-click on a single path, compound path, image, mesh or placed file now
isolates it too, as the public documentation describes. Type still switches to
the Type tool; blends, envelopes, repeats and symbol instances keep their own
editing modes.

While a single object is isolated only it is hit, marqueed and taken by Select
All, new art goes beside it in its group or layer, and a double-click on the
empty canvas leaves with it selected. object.isolate accepts any object except
type.

crates/engine/src/tests_prefs.rs

@@ -298,6 +298,60 @@ fn selection_preferences_drive_the_selection_tool() {
     assert!(double(&mut s).is_some(), "on: the group is isolated");
 }
 
+/// Double Click To Isolate: a double-click with the Selection tool isolates a single object too,
+/// not only a group. Inside, only it is hit, marqueed and selected by Select All; new art goes
+/// beside it; a double-click on the empty canvas leaves, with it selected. Type isn't isolated:
+/// a double-click on it switches to the Type tool.
+#[test]
+fn double_clicking_a_single_object_isolates_it() {
+    use vectorcraft_tools::{PointerEvent, PointerKind};
+    let mut s = Session::new();
+    s.execute("file.new", &json!({"width": 400, "height": 400})).unwrap();
+    let id = |v: Value| NodeId(v["id"].as_u64().unwrap());
+    let rect = |s: &mut Session, x: f64| id(s.execute("shape.rectangle", &json!({"x": x, "y": 100, "width": 50, "height": 50})).unwrap());
+    let (a, b) = (rect(&mut s, 100.0), rect(&mut s, 200.0));
+    s.select_tool("selection", ViewInfo::default()).unwrap();
+    let ev = |s: &mut Session, kinds: &[PointerKind], x: f64, y: f64| {
+        for k in kinds {
+            s.pointer(&PointerEvent::new(*k, x, y), ViewInfo::default()).unwrap();
+        }
+    };
+    let click = [PointerKind::Down, PointerKind::Up];
+    let double = [PointerKind::DoubleClick];
+    ev(&mut s, &double, 125.0, 125.0);
+    assert_eq!(s.doc().unwrap().isolation, Some(a));
+    // Only the isolated object is hit: a click on the other selects nothing.
+    ev(&mut s, &click, 225.0, 125.0);
+    assert!(s.doc().unwrap().selection.objects.is_empty());
+    ev(&mut s, &click, 125.0, 125.0);
+    assert_eq!(s.doc().unwrap().selection.objects, vec![a]);
+    // A marquee over both and Select All take it alone.
+    s.execute("select.none", &json!({})).unwrap();
+    ev(&mut s, &[PointerKind::Down], 90.0, 90.0);
+    ev(&mut s, &[PointerKind::Move, PointerKind::Up], 300.0, 300.0);
+    assert_eq!(s.doc().unwrap().selection.objects, vec![a]);
+    s.execute("select.none", &json!({})).unwrap();
+    s.execute("select.all", &json!({})).unwrap();
+    assert_eq!(s.doc().unwrap().selection.objects, vec![a]);
+    // A second double-click on it stays in isolation; new art lands on its layer.
+    ev(&mut s, &double, 125.0, 125.0);
+    assert_eq!(s.doc().unwrap().isolation, Some(a));
+    let c = rect(&mut s, 300.0);
+    let st = s.doc().unwrap();
+    assert_eq!(st.doc.parent_of(c), st.doc.parent_of(a));
+    // A double-click on the empty canvas leaves isolation, the object selected.
+    ev(&mut s, &double, 50.0, 350.0);
+    let st = s.doc().unwrap();
+    assert_eq!((st.isolation, st.selection.objects.clone()), (None, vec![a]));
+    assert!(st.doc.node(b).is_some());
+    // Type is not isolated.
+    let t = id(s.execute("text.create", &json!({"x": 100, "y": 300, "text": "Type"})).unwrap());
+    assert!(s.execute("object.isolate", &json!({"id": t.0})).is_err());
+    s.execute("prefs.set", &json!({"key": "doubleClickToIsolate", "value": false})).unwrap();
+    ev(&mut s, &double, 225.0, 125.0);
+    assert_eq!(s.doc().unwrap().isolation, None, "off: no isolation");
+}
+
 /// General › Use Precise Cursors (#394): the Pen's pointer becomes a crosshair; the Selection
 /// tool's arrow stays.
 #[test]