Fix updates to Overlay with variable items (#3701)

* Fix updates to Overlay with variable items

* Add test

holoviews/plotting/bokeh/element.py

@@ -2130,16 +2130,16 @@ def update_frame(self, key, ranges=None, element=None):
         if element is not None:
             ranges = self.compute_ranges(range_obj, key, ranges)
 
-        # Update plot options
-        plot_opts = self.lookup_options(element, 'plot').options
-        inherited = self._traverse_options(element, 'plot',
-                                           self._propagate_options,
-                                           defaults=False)
-        plot_opts.update(**{k: v[0] for k, v in inherited.items() if k not in plot_opts})
-        self.param.set_param(**plot_opts)
-
-        if element and not self.overlaid and not self.tabs and not self.batched:
-            self._update_ranges(element, ranges)
+            # Update plot options
+            plot_opts = self.lookup_options(element, 'plot').options
+            inherited = self._traverse_options(element, 'plot',
+                                               self._propagate_options,
+                                               defaults=False)
+            plot_opts.update(**{k: v[0] for k, v in inherited.items() if k not in plot_opts})
+            self.param.set_param(**plot_opts)
+
+            if not self.overlaid and not self.tabs and not self.batched:
+                self._update_ranges(element, ranges)
 
         # Determine which stream (if any) triggered the update
         triggering = [stream for stream in self.streams if stream._triggering]

holoviews/tests/plotting/bokeh/testoverlayplot.py

@@ -3,6 +3,7 @@
 from holoviews.core import NdOverlay, HoloMap, DynamicMap, Overlay
 from holoviews.core.options import Cycle
 from holoviews.element import Curve, Points, ErrorBars, Text, VLine
+from holoviews.streams import Stream
 from holoviews.util import Dynamic
 
 from .testplot import TestBokehPlot, bokeh_renderer
@@ -278,3 +279,12 @@ def test_dynamicmap_legend_updates_add_dynamic_plots(self):
         legend_labels = [item.label for item in plot.state.legend[0].items]
         self.assertEqual(legend_labels, [{'value': 'A'}, {'value': 'B'}, {'value': 'C'}])
 
+    def test_dynamicmap_ndoverlay_shrink_number_of_items(self):
+        selected = Stream.define('selected', items=3)()
+        def callback(items):
+            return NdOverlay({j: Overlay([Curve([1, 2, j])]) for j in range(items)})
+        dmap = DynamicMap(callback, streams=[selected])
+        plot = bokeh_renderer.get_plot(dmap)
+        selected.event(items=2)
+        self.assertEqual(len([r for r in plot.state.renderers if r.visible]), 2)
+