OWBoxPlot: Fix crash with missing values

Orange/widgets/visualize/owboxplot.py

@@ -136,6 +136,9 @@ class OWBoxPlot(widget.OWWidget):
 
     graph_name = "box_scene"
 
+    class Warning(widget.OWWidget.Warning):
+        missing_values = widget.Msg("Variable consists of only missing values.")
+
     def __init__(self):
         super().__init__()
         self.stats = []
@@ -292,11 +295,28 @@ def clear_scene(self):
         self.posthoc_lines = []
 
     def layout_changed(self):
-        attr = self.attribute
-        if not attr:
-            return
         self.clear_scene()
+
         if self.dataset is None or len(self.conts) == len(self.dist) == 0:
+            self.Warning.missing_values.clear()
+            return
+
+        if len(self.conts):
+            if sum(self.conts.unknowns) == \
+                    len(self.dataset) and self.is_continuous:
+                self.Warning.missing_values()
+                return
+        if len(self.dist):
+            if self.dist.unknowns == len(self.dataset) and self.is_continuous:
+                self.Warning.missing_values()
+                return
+
+        self.Warning.missing_values.clear()
+        self.layout_changed_repaint()
+
+    def layout_changed_repaint(self):
+        attr = self.attribute
+        if not attr:
             return
 
         if not self.is_continuous:

Orange/widgets/visualize/tests/test_owboxplot.py

@@ -0,0 +1,51 @@
+# Test methods with long descriptive names can omit docstrings
+# pylint: disable=missing-docstring
+import numpy as np
+from Orange.data import Table, ContinuousVariable
+from Orange.widgets.visualize.owboxplot import OWBoxPlot
+from Orange.widgets.tests.base import WidgetTest
+
+
+class TestOWBoxPlot(WidgetTest):
+    def setUp(self):
+        self.widget = self.create_widget(OWBoxPlot)
+        self.iris = Table("iris")
+        self.zoo = Table("zoo")
+        self.housing = Table("housing")
+
+    def test_input_data(self):
+        """Check widget's data"""
+        self.assertEqual(self.widget.dataset, None)
+        self.send_signal("Data", self.iris)
+        self.assertEqual(self.widget.dataset, self.iris)
+        self.send_signal("Data", None)
+        self.assertEqual(self.widget.dataset, None)
+
+    def test_input_data_missings_cont_group_var(self):
+        """Check widget with continuous data with missing values and group variable"""
+        data = self.iris
+        data.X[:, 0] = np.nan
+        self.send_signal("Data", data)
+        self.assertEqual(self.widget.dataset, data)
+
+    def test_input_data_missings_cont_no_group_var(self):
+        """Check widget with continuous data with missing values and no group variable"""
+        data = self.housing
+        data.X[:, 0] = np.nan
+        self.send_signal("Data", data)
+        self.assertEqual(self.widget.dataset, data)
+
+    def test_input_data_missings_disc_group_var(self):
+        """Check widget with discrete data with missing values and group variable"""
+        data = self.zoo
+        data.X[:, 0] = np.nan
+        self.send_signal("Data", data)
+        self.assertEqual(self.widget.dataset, data)
+
+    def test_input_data_missings_disc_no_group_var(self):
+        """Check widget discrete data with missing values and no group variable"""
+        data = self.zoo
+        data.domain.class_var = ContinuousVariable("cls")
+        data.X[:, 0] = np.nan
+        self.send_signal("Data", data)
+        self.assertEqual(self.widget.dataset, data)