manually set the text format to plain text in error

traitsui/qt4/editor.py

@@ -24,7 +24,7 @@
 """
 
 
-from pyface.qt import QtGui
+from pyface.qt import QtCore, QtGui
 
 from traits.api import HasTraits, Instance, Str, Callable
 
@@ -78,9 +78,16 @@ def error(self, excp):
         else:
             control = self.control
 
-        QtGui.QMessageBox.information(
-            control, self.description + " value error", str(excp)
+        message_box = QtGui.QMessageBox(
+            QtGui.QMessageBox.Information,
+            self.description + " value error",
+            str(excp),
+            buttons=QtGui.QMessageBox.Ok,
+            parent=control
         )
+        message_box.setTextFormat(QtCore.Qt.PlainText)
+        message_box.setEscapeButton(QtGui.QMessageBox.Ok)
+        message_box.exec_()
 
     def set_tooltip_text(self, control, text):
         """ Sets the tooltip for a specified control.

traitsui/tests/test_editor.py

@@ -10,17 +10,33 @@
 
 import unittest
 
-from traits.api import Any, Bool, Event, Float, HasTraits, Int, List, Undefined
+from pyface.toolkit import toolkit_object
+from traits.api import (
+    Any, Bool, Event, Float, HasTraits, Int, List, Range, Undefined
+)
 from traits.trait_base import xgetattr
 
 from traitsui.context_value import ContextValue, CVFloat, CVInt
 from traitsui.editor import Editor
 from traitsui.editor_factory import EditorFactory
 from traitsui.handler import default_handler
 from traitsui.ui import UI
+from traitsui.testing.api import (
+    KeyClick, KeySequence, Textbox, UITester
+)
 from traitsui.tests._tools import (
-    BaseTestMixin, GuiTestAssistant, no_gui_test_assistant
+    BaseTestMixin,
+    GuiTestAssistant,
+    is_mac_os,
+    no_gui_test_assistant,
+    requires_toolkit,
+    ToolkitName,
+)
+
+ModalDialogTester = toolkit_object(
+    "util.modal_dialog_tester:ModalDialogTester"
 )
+no_modal_dialog_tester = ModalDialogTester.__name__ == "Unimplemented"
 
 
 class FakeControl(HasTraits):
@@ -917,3 +933,48 @@ def test_sync_value_both(self):
 
         with self.assertTraitDoesNotChange(user_object, "user_auxiliary"):
             editor.auxiliary_value = 14
+
+    # regression test for enthought/traitsui#1543
+    @requires_toolkit([ToolkitName.qt])
+    @unittest.skipIf(no_modal_dialog_tester, "ModalDialogTester unavailable")
+    @unittest.skipIf(is_mac_os, "There is a separate issue on OSX")
+    def test_editor_error_msg(self):
+        from pyface.qt import QtGui
+
+        class Foo(HasTraits):
+            x = Range(low=0.0, high=1.0, value=0.5, exclude_low=True)
+
+        foo = Foo()
+        tester = UITester()
+        with tester.create_ui(foo) as ui:
+
+            x_range = tester.find_by_name(ui, "x")
+            x_range_textbox = x_range.locate(Textbox())
+
+            for _ in range(3):
+                x_range_textbox.perform(KeyClick('Backspace'))
+
+            x_range_textbox.perform(KeySequence('0.0'))
+
+            def trigger_error():
+                x_range_textbox.perform(KeyClick('Enter'))
+
+            def check_and_close(mdtester):
+                try:
+                    with mdtester.capture_error():
+                        self.assertTrue(
+                            mdtester.has_widget(
+                                text="The 'x' trait of a Foo instance must be "
+                                     "0.0 < a floating point number <= 1.0, "
+                                     "but a value of 0.0 <class 'float'> was "
+                                     "specified.",
+                                type_=QtGui.QMessageBox,
+                            )
+                        )
+                finally:
+                    mdtester.close(accept=True)
+                    self.assertTrue(mdtester.dialog_was_opened)
+
+            mdtester = ModalDialogTester(trigger_error)
+            mdtester.open_and_run(check_and_close)
+            self.assertTrue(mdtester.dialog_was_opened)