Panels: a double-click on the strip of a group beside another does nothing

Such a group can't collapse, so the strip queued window.panel.collapse only for the command to refuse it and leave an error in the status bar.

crates/ui-egui/src/panel_docking.rs

@@ -896,7 +896,8 @@ fn root_groups(ctx: &egui::Context, layout: &Layout<String>, content: egui::Rect
 /// and left of its panel menu, from which Illustrator also collapses the group
 /// (<https://helpx.adobe.com/illustrator/using/customizing-workspace.html>). Most of it has no
 /// widget of its own, so the press is read from the input; `layer` is the dock's, so a press on a
-/// floating group or a menu over the strip doesn't count. Accordions are left out.
+/// floating group or a menu over the strip doesn't count. Accordions, and groups beside another
+/// (which don't collapse), are left out.
 fn tab_area_double_clicked(
     ctx: &egui::Context,
     layer: egui::LayerId,
@@ -909,7 +910,9 @@ fn tab_area_double_clicked(
         return None;
     }
     let group = groups.iter().find(|g| g.strip.contains(at))?;
-    tab_group_shortens(layout, group.shown)?;
+    if tab_group_shortens(layout, group.shown) != Some(true) {
+        return None;
+    }
     let area = egui::Id::new("vectorcraft-panel-docking");
     let right = |id: egui::Id| ctx.read_response(id).map(|r| r.rect.right());
     let tabs = group

crates/ui-egui/src/panel_docking_tests.rs

@@ -1200,3 +1200,23 @@ fn a_group_beside_another_does_not_collapse() {
     crate::panel_docking::prune_collapsed(&mut app.ui);
     assert!(app.ui.docking_collapsed.is_empty());
 }
+
+/// A double-click on the strip of a group beside another does nothing, and leaves no error in the
+/// status bar.
+#[test]
+fn a_double_click_on_the_strip_of_a_group_beside_another_does_nothing() {
+    let mut app = app();
+    app.run("file.new", json!({"width": 400, "height": 300})).unwrap();
+    app.run("window.panel.move", json!({"panel":"swatches", "anchor":"layers", "zone":"left"})).unwrap();
+    let saved = app.ui.docking.clone();
+    let mut h = harness(app, vec2(1280.0, 800.0));
+    let status = h.state().ui.status.clone();
+    let strip = root_groups(&h).into_iter().find(|g| g.shown == "swatches").unwrap().strip;
+    let tab = h.ctx.read_response(egui::Id::new("vectorcraft-panel-docking").with(("tab", &"swatches".to_string()))).unwrap().rect;
+    let gap = pos2(tab.right() + 4.0, strip.center().y);
+    assert!(gap.x < strip.right() - 24.0, "{tab:?} {strip:?}");
+    double_click(&mut h, gap);
+    assert_eq!(h.state().ui.status, status, "no error");
+    assert!(h.state().ui.docking_collapsed.is_empty());
+    assert_eq!(h.state().ui.docking, saved);
+}