Implement refresh in object explorer

* In CollectionDelegate, pass `data_function` when creating an object explorer.
* Add a refresh toolbutton to the object explorer, which calls the new
  function `.refresh_editor()`.
* In the new function, call `data_function` and use its return value as the
  new object to be displayed in the object explorer. Handle exceptions thrown
  by `data_function`.
* Add tests for the new refresh functionality.

spyder/plugins/variableexplorer/widgets/collectionsdelegate.py

@@ -318,6 +318,7 @@ def createEditor(self, parent, option, index, object_explorer=False):
                 name=key,
                 parent=parent,
                 namespacebrowser=self.namespacebrowser,
+                data_function=self.make_data_function(index),
                 readonly=readonly)
             self.create_dialog(editor, dict(model=index.model(),
                                             editor=editor,

spyder/plugins/variableexplorer/widgets/objectexplorer/objectexplorer.py

@@ -11,14 +11,15 @@
 # Standard library imports
 import logging
 import traceback
+from typing import Any, Callable, Optional
 
 # Third-party imports
 from qtpy.QtCore import Slot, QModelIndex, QPoint, QSize, Qt
 from qtpy.QtGui import QKeySequence, QTextOption
-from qtpy.QtWidgets import (QAbstractItemView, QAction, QButtonGroup,
-                            QGroupBox, QHBoxLayout, QHeaderView,
-                            QMenu, QPushButton, QRadioButton, QSplitter,
-                            QToolButton, QVBoxLayout, QWidget)
+from qtpy.QtWidgets import (
+    QAbstractItemView, QAction, QButtonGroup, QGroupBox, QHBoxLayout,
+    QHeaderView, QMenu, QMessageBox, QPushButton, QRadioButton, QSplitter,
+    QToolButton, QVBoxLayout, QWidget)
 
 # Local imports
 from spyder.api.config.fonts import SpyderFontsMixin, SpyderFontType
@@ -62,6 +63,7 @@ def __init__(self,
                  resize_to_contents=True,
                  parent=None,
                  namespacebrowser=None,
+                 data_function: Optional[Callable[[], Any]] = None,
                  attribute_columns=DEFAULT_ATTR_COLS,
                  attribute_details=DEFAULT_ATTR_DETAILS,
                  readonly=None,
@@ -94,6 +96,7 @@ def __init__(self,
         self.name = name
         self.expanded = expanded
         self.namespacebrowser = namespacebrowser
+        self.data_function = data_function
         self._attr_cols = attribute_columns
         self._attr_details = attribute_details
         self.readonly = readonly
@@ -258,6 +261,14 @@ def _setup_menu(self, show_callable_attributes=False,
         self.tools_layout.addSpacing(5)
         self.tools_layout.addWidget(special_attributes)
 
+        self.refresh_button = create_toolbutton(
+            self, icon=ima.icon('refresh'),
+            tip=_('Refresh editor with current value of variable in console'),
+            triggered=self.refresh_editor)
+        self.refresh_button.setEnabled(self.data_function is not None)
+        self.tools_layout.addSpacing(5)
+        self.tools_layout.addWidget(self.refresh_button)
+
         self.tools_layout.addStretch()
 
         self.options_button = create_toolbutton(
@@ -406,6 +417,22 @@ def _readViewSettings(self, reset=False):
         if button is not None:
             button.setChecked(True)
 
+    def refresh_editor(self) -> None:
+        """
+        Refresh data in editor.
+        """
+        assert self.data_function is not None
+
+        try:
+            data = self.data_function()
+        except (IndexError, KeyError):
+            QMessageBox.critical(self, _('Collection editor'),
+                                 _('The variable no longer exists.'))
+            self.reject()
+            return
+
+        self.set_value(data)
+
     @Slot()
     def save_and_close_enable(self):
         """Handle the data change event to enable the save and close button."""

spyder/plugins/variableexplorer/widgets/objectexplorer/tests/test_objectexplorer.py

@@ -11,12 +11,15 @@
 """
 
 # Standard library imports
+from dataclasses import dataclass
 import datetime
+from unittest.mock import patch
 
 # Third party imports
-from qtpy.QtCore import Qt
 import numpy as np
 import pytest
+from qtpy.QtCore import Qt
+from qtpy.QtWidgets import QMessageBox
 
 # Local imports
 from spyder.config.manager import CONF
@@ -172,5 +175,60 @@ def __init__(self):
     assert model.columnCount() == 11
 
 
+@dataclass
+class DataclassForTesting:
+    name: str
+    price: float
+    quantity: int
+
+
+def test_objectexplorer_refreshbutton_disabled():
+    """
+    Test that the Refresh button is disabled by default.
+    """
+    data = DataclassForTesting('lemon', 0.15, 5)
+    editor = ObjectExplorer(data, name='data')
+    assert not editor.refresh_button.isEnabled()
+
+
+def test_objectexplorer_refresh():
+    """
+    Test that after pressing the refresh button, the value of the Array Editor
+    is replaced by the return value of the data_function.
+    """
+    data_old = DataclassForTesting('lemon', 0.15, 5)
+    data_new = range(1, 42, 3)
+    editor = ObjectExplorer(data_old, name='data',
+                            data_function=lambda: data_new)
+    model = editor.obj_tree.model()
+    root = model.index(0, 0)
+    assert model.data(model.index(0, 0, root), Qt.DisplayRole) == 'name'
+    assert model.data(model.index(0, 3, root), Qt.DisplayRole) == 'lemon'
+    assert editor.refresh_button.isEnabled()
+    editor.refresh_editor()
+    model = editor.obj_tree.model()
+    root = model.index(0, 0)
+    row = model.rowCount(root) - 1
+    assert model.data(model.index(row, 0, root), Qt.DisplayRole) == 'stop'
+    assert model.data(model.index(row, 3, root), Qt.DisplayRole) == '42'
+
+
+def test_objectexplorer_refresh_when_variable_deleted(qtbot):
+    """
+    Test that if the variable is deleted and then the editor is refreshed
+    (resulting in data_function raising a KeyError), a critical dialog box
+    is displayed and that the object editor is closed.
+    """
+    def datafunc():
+        raise KeyError
+    data = DataclassForTesting('lemon', 0.15, 5)
+    editor = ObjectExplorer(data, name='data', data_function=datafunc)
+    with patch('spyder.plugins.variableexplorer.widgets.objectexplorer'
+               '.objectexplorer.QMessageBox.critical') as mock_critical:
+        with qtbot.waitSignal(editor.rejected, timeout=0):
+            editor.refresh_button.click()
+    mock_critical.assert_called_once()
+
+
 if __name__ == "__main__":
     pytest.main()