misc: use existing computed data fields when evaluating further fields (#55440)

tests/form_pages/test_computed_field.py

@@ -477,3 +477,49 @@ def test_computed_field_edit_action(pub):
     resp = resp.forms[0].submit('submit')
     formdata.refresh_from_storage()
     assert formdata.data == {'0': 'bar', '1': 'PLOP'}
+
+
+def test_cascading_computed_fields(pub):
+    FormDef.wipe()
+    formdef = FormDef()
+    formdef.name = 'test'
+    formdef.fields = [
+        fields.PageField(
+            id='0',
+            label='1st page',
+            type='page',
+            post_conditions=[
+                {
+                    'condition': {
+                        'type': 'django',
+                        'value': 'form_var_dc == "0abc"',
+                    },
+                    'error_message': 'You shall not pass.',
+                }
+            ],
+        ),
+        fields.ComputedField(id='1', label='computed', varname='a', value_template='a'),
+        fields.ComputedField(id='2', label='computed', varname='b', value_template='{{form_var_a}}b'),
+        fields.ComputedField(id='3', label='computed', varname='c', value_template='{{form_var_b}}c'),
+        fields.CommentField(id='4', label='X{{ form_var_c }}Y', type='comment'),
+        fields.StringField(id='5', label='string', varname='d'),
+        fields.ComputedField(id='6', label='computed', varname='da', value_template='{{form_var_d}}a'),
+        fields.ComputedField(id='7', label='computed', varname='db', value_template='{{form_var_da}}b'),
+        fields.ComputedField(id='8', label='computed', varname='dc', value_template='{{form_var_db}}c'),
+    ]
+    formdef.store()
+    formdef.data_class().wipe()
+
+    resp = get_app(pub).get('/test/')
+    assert 'XabcY' in resp.text  # check comment field has the correct value
+
+    # this should produce form_var_dc == "Xabc", and not pass the post condition
+    resp.forms[0]['f5'].value = 'X'
+    resp = resp.forms[0].submit('submit')  # -> validation
+    assert 'You shall not pass.' in resp.text
+
+    # this should produce form_var_dc == "0abc", and be ok for the post condition
+    resp = get_app(pub).get('/test/')
+    resp.forms[0]['f5'].value = '0'
+    resp = resp.forms[0].submit('submit')  # -> validation
+    assert 'You shall not pass.' not in resp.text

wcs/forms/root.py

@@ -641,17 +641,33 @@ class FormPage(Directory, FormTemplateMixin):
             return computed_values
         if not computed_values:
             get_session().add_magictoken('%s-computed' % magictoken, computed_values)
+
+        # create a temporary map using form variable names, to be used as context
+        # variables during evaluation (via temporary_feed below), so we can have
+        # computed fields depending on previously computed fields from the same page.
+        mapped_computed_values = {}
         for field in fields:
-            if field.freeze_on_initial_value and field.id in computed_values:
-                continue
-            with get_publisher().complex_data():
-                try:
-                    value = WorkflowStatusItem.compute(field.value_template, raises=True, allow_complex=True)
-                except TemplateError:
+            if field.id in computed_values:
+                mapped_computed_values['form_var_%s' % field.varname] = computed_values[field.id]
+
+        with get_publisher().substitutions.temporary_feed(mapped_computed_values, force_mode='lazy'):
+            for field in fields:
+                if field.freeze_on_initial_value and field.id in computed_values:
                     continue
-                else:
-                    value = get_publisher().get_cached_complex_data(value)
-                computed_values[field.id] = value
+
+                with get_publisher().complex_data():
+                    try:
+                        value = WorkflowStatusItem.compute(
+                            field.value_template, raises=True, allow_complex=True
+                        )
+                    except TemplateError:
+                        continue
+                    else:
+                        value = get_publisher().get_cached_complex_data(value)
+                    computed_values[field.id] = value
+                    mapped_computed_values['form_var_%s' % field.varname] = value
+                    get_publisher().substitutions.invalidate_cache()
+
         return computed_values
 
     def modify_filling_context(self, context, page, data):