xdg_toplevel: automatically float windows based on xdg-dialog and requested size

src/ifs/wl_surface/xdg_surface/xdg_toplevel.rs

@@ -417,6 +417,29 @@ impl XdgToplevel {
             }
             return;
         }
+        let is_dialog = self.dialog.is_some();
+        let fixed_size = match (
+            self.min_width.get(),
+            self.max_width.get(),
+            self.min_height.get(),
+            self.max_height.get(),
+        ) {
+            (Some(min_w), Some(max_w), Some(min_h), Some(max_h)) if min_w == max_w && min_h == max_h => {
+                Some((min_w, min_h))
+            }
+            _ => None,
+        };
+        if is_dialog || fixed_size.is_some() {
+            let ws = parent
+                .and_then(|p| p.xdg.workspace.get())
+                .unwrap_or_else(|| self.state.ensure_map_workspace(None));
+            if let Some((w, h)) = fixed_size {
+                self.toplevel_data.float_width.set(w);
+                self.toplevel_data.float_height.set(h);
+            }
+            self.map_floating(&ws, pos.map(|p| (p.1, p.2)));
+            return;
+        }
         match parent {
             None => self.map_tiled(),
             Some(p) => self.map_child(p, pos),