misc: don't advertise _live_ variables if card is missing (#45296)

tests/test_formdata.py

@@ -814,6 +814,8 @@ def test_lazy_formdata_live_item(pub):
     formdata.data = {
         '0': str(carddata.id),
     }
+    formdata.data['0_display'] = formdef.fields[0].store_display_value(formdata.data, '0')
+    formdata.data['0_structured'] = formdef.fields[0].store_structured_value(formdata.data, '0')
     pub.substitutions.feed(pub)
     pub.substitutions.feed(formdef)
     pub.substitutions.feed(formdata)
@@ -823,11 +825,13 @@ def test_lazy_formdata_live_item(pub):
     assert context['form_var_foo_live_number'] == carddata.get_display_id()
     assert context['form_var_foo_live_var_name'] == 'baz'
     assert context['form_var_foo_live_var_attr'] == 'attr2'
+    assert 'form_var_foo_live_var_attr' in context.get_flat_keys()
 
     CardDef.wipe()
     context = pub.substitutions.get_context_variables(mode='lazy')
     with pytest.raises(KeyError):
         context['form_var_foo_live_name']
+    assert 'form_var_foo_live_var_attr' not in context.get_flat_keys()
 
 
 def test_lazy_formdata_queryset(pub, variable_test_data):

wcs/variables.py

@@ -651,7 +651,13 @@ class LazyFieldVarStructured(LazyFieldVar):
 
         keys = ['raw', 'structured']
         if self._field.data_source and self._field.data_source.get('type', '').startswith('carddef:'):
-            keys.append('live')
+            try:
+                self.live
+            except AttributeError:
+                # don't advertise "live" if linked data is missing
+                pass
+            else:
+                keys.append('live')
 
         def walk(base, value):
             if isinstance(value, dict):