workflows: make sure anchor expression is imported as a string (#39360)

tests/test_workflow_import.py

@@ -628,6 +628,19 @@ def test_global_timeout_trigger(pub):
     assert wf2.global_actions[0].triggers[-1].anchor == trigger.anchor
 
 
+def test_global_anchor_expression_trigger(pub):
+    wf = Workflow(name='global actions')
+    ac1 = wf.add_global_action('Action', 'ac1')
+    trigger = ac1.append_trigger('timeout')
+    trigger.anchor_expression = 'False'
+    trigger.anchor = 'python'
+
+    wf2 = assert_import_export_works(wf, include_id=True)
+    assert wf2.global_actions[0].triggers[-1].id == trigger.id
+    assert wf2.global_actions[0].triggers[-1].anchor == trigger.anchor
+    assert wf2.global_actions[0].triggers[-1].anchor_expression == trigger.anchor_expression
+
+
 def test_global_webservice_trigger(pub):
     wf = Workflow(name='global actions')
     ac1 = wf.add_global_action('Action', 'ac1')

wcs/workflows.py

@@ -889,7 +889,8 @@ class XmlSerialisable(object):
             else:
                 if el.text is None:
                     setattr(self, attribute, None)
-                elif el.text in ('False', 'True'): # bools
+                elif el.text in ('False', 'True') and not isinstance(getattr(self, attribute), six.string_types):
+                    # booleans
                     setattr(self, attribute, el.text == 'True')
                 elif type(getattr(self, attribute)) is int:
                     setattr(self, attribute, int(el.text))
@@ -1041,7 +1042,7 @@ class WorkflowGlobalActionTimeoutTriggerMarker(object):
 class WorkflowGlobalActionTimeoutTrigger(WorkflowGlobalActionTrigger):
     key = 'timeout'
     anchor = None
-    anchor_expression = None
+    anchor_expression = ''
     anchor_status_first = None
     anchor_status_latest = None
     timeout = None