Fix PropertyValueColumnData._stream() to handle rollover >= len(L) (

#13318)

* Fix PropertyValueColumnData._stream() to handle rollover >= len(data)

* Clean implementation

src/bokeh/core/property/wrappers.py

@@ -477,7 +477,7 @@ def _stream(self, doc: Document, source: ColumnarDataSource, new_data: dict[str,
             else:
                 L = self[k]
                 L.extend(new_data[k])
-                if rollover is not None:
+                if rollover is not None and len(L) > rollover:
                     del L[:len(L) - rollover]
 
         from ...document.events import ColumnsStreamedEvent

tests/unit/bokeh/core/property/test_wrappers__property.py

@@ -249,6 +249,24 @@ def test_PropertyValueColumnData__stream_list_with_rollover_equals_zero(mock_not
     assert event.rollover == 0
     assert event.data == {'foo': [40]}
 
+@patch('bokeh.core.property.wrappers.PropertyValueContainer._notify_owners')
+def test_PropertyValueColumnData__stream_list_with_rollover_greater_than_list_length(mock_notify: MagicMock) -> None:
+    from bokeh.document.events import ColumnsStreamedEvent
+
+    source = ColumnDataSource(data=dict(foo=[10, 20, 30]))
+    pvcd = bcpw.PropertyValueColumnData(source.data)
+
+    mock_notify.reset_mock()
+    pvcd._stream("doc", source, dict(foo=[40]), rollover=5, setter="setter")
+    assert mock_notify.call_count == 1
+    assert mock_notify.call_args[0] == ({'foo': [10, 20, 30, 40]},) # streaming to list, "old" is actually updated value
+    assert 'hint' in mock_notify.call_args[1]
+    event = mock_notify.call_args[1]['hint']
+    assert isinstance(event, ColumnsStreamedEvent)
+    assert event.setter == 'setter'
+    assert event.rollover == 5
+    assert event.data == {'foo': [40]}
+
 @patch('bokeh.core.property.wrappers.PropertyValueContainer._notify_owners')
 def test_PropertyValueColumnData__stream_array_to_array(mock_notify: MagicMock) -> None:
     import numpy as np
@@ -335,6 +353,28 @@ def test_PropertyValueColumnData__stream_array_with_rollover_equals_zero(mock_no
     assert event.rollover == 0
     assert event.data == {'foo': [40]}
 
+@patch('bokeh.core.property.wrappers.PropertyValueContainer._notify_owners')
+def test_PropertyValueColumnData__stream_array_greater_than_array_length(mock_notify: MagicMock) -> None:
+    import numpy as np
+
+    from bokeh.document.events import ColumnsStreamedEvent
+
+    source = ColumnDataSource(data=dict(foo=np.array([10, 20, 30])))
+    pvcd = bcpw.PropertyValueColumnData(source.data)
+
+    mock_notify.reset_mock()
+    pvcd._stream("doc", source, dict(foo=[40]), rollover=5, setter="setter")
+    assert mock_notify.call_count == 1
+    assert len(mock_notify.call_args[0]) == 1
+    assert 'foo' in mock_notify.call_args[0][0]
+    assert (mock_notify.call_args[0][0]['foo'] == np.array([10, 20, 30])).all()
+    assert 'hint' in mock_notify.call_args[1]
+    event = mock_notify.call_args[1]['hint']
+    assert isinstance(event, ColumnsStreamedEvent)
+    assert event.setter == 'setter'
+    assert event.rollover == 5
+    assert event.data == {'foo': [40]}
+
 @patch('bokeh.core.property.wrappers.PropertyValueContainer._notify_owners')
 def test_PropertyValueColumnData__patch_with_simple_indices(mock_notify: MagicMock) -> None:
     from bokeh.document.events import ColumnsPatchedEvent