layout: Fix crash when a window opens next-to an only interactively moved window with no outputs

src/layout/mod.rs

@@ -1142,7 +1142,15 @@ impl<W: LayoutElement> Layout<W> {
                             .filter(|move_| next_to == move_.tile.window().id())
                             .is_some()
                         {
-                            // The next_to window is being interactively moved.
+                            // The next_to window is being interactively moved. If there are no
+                            // other windows, we may have no workspaces at all.
+                            if workspaces.is_empty() {
+                                workspaces.push(Workspace::new_no_outputs(
+                                    self.clock.clone(),
+                                    self.options.clone(),
+                                ));
+                            }
+
                             (0, WorkspaceAddWindowTarget::Auto)
                         } else {
                             let ws_idx = workspaces

src/layout/tests.rs

@@ -2937,6 +2937,39 @@ fn interactive_move_drop_on_other_output_during_animation() {
     check_ops(&ops);
 }
 
+#[test]
+fn add_window_next_to_only_interactively_moved_without_outputs() {
+    let ops = [
+        Op::AddWindow {
+            params: TestWindowParams::new(2),
+        },
+        Op::AddOutput(1),
+        Op::InteractiveMoveBegin {
+            window: 2,
+            output_idx: 1,
+            px: 0.0,
+            py: 0.0,
+        },
+        Op::InteractiveMoveUpdate {
+            window: 2,
+            dx: 0.0,
+            dy: 3586.692842955048,
+            output_idx: 1,
+            px: 0.0,
+            py: 0.0,
+        },
+        Op::RemoveOutput(1),
+        // We have no outputs, and the only existing window is interactively moved, meaning there
+        // are no workspaces either.
+        Op::AddWindowNextTo {
+            params: TestWindowParams::new(3),
+            next_to_id: 2,
+        },
+    ];
+
+    check_ops(&ops);
+}
+
 #[test]
 fn set_width_fixed_negative() {
     let ops = [