fix: display "global" errors at top of form, if present

this probably could use more work, good enough for now

src/wuttaweb/forms/base.py

@@ -1111,6 +1111,32 @@ class Form:
 
         return self.validated
 
+    def has_global_errors(self):
+        """
+        Convenience function to check if the form has any "global"
+        (not field-level) errors.
+
+        See also :meth:`get_global_errors()`.
+
+        :returns: ``True`` if global errors present, else ``False``.
+        """
+        dform = self.get_deform()
+        return bool(dform.error)
+
+    def get_global_errors(self):
+        """
+        Returns a list of "global" (not field-level) error messages
+        for the form.
+
+        See also :meth:`has_global_errors()`.
+
+        :returns: List of error messages (possibly empty).
+        """
+        dform = self.get_deform()
+        if dform.error is None:
+            return []
+        return dform.error.messages()
+
     def get_field_errors(self, field):
         """
         Return a list of error messages for the given field.

src/wuttaweb/templates/forms/vue_template.mako

@@ -4,6 +4,14 @@
   ${h.form(form.action_url, method='post', enctype='multipart/form-data', **form_attrs)}
     ${h.csrf_token(request)}
 
+    % if form.has_global_errors():
+        % for msg in form.get_global_errors():
+            <b-notification type="is-warning" :closable="false">
+              ${msg}
+            </b-notification>
+        % endfor
+    % endif
+
     <section>
       % for fieldname in form:
           ${form.render_vue_field(fieldname)}

tests/forms/test_base.py

@@ -544,6 +544,34 @@ class TestForm(TestCase):
         data = form.get_vue_model_data()
         self.assertEqual(list(data.values()), ['one', 'two', True])
 
+    def test_has_global_errors(self):
+
+        def fail(node, value):
+            node.raise_invalid("things are bad!")
+
+        schema = self.make_schema()
+        schema.validator = fail
+        form = self.make_form(schema=schema)
+        self.assertFalse(form.has_global_errors())
+        self.request.method = 'POST'
+        self.request.POST = {'foo': 'one', 'bar': 'two'}
+        self.assertFalse(form.validate())
+        self.assertTrue(form.has_global_errors())
+
+    def test_get_global_errors(self):
+
+        def fail(node, value):
+            node.raise_invalid("things are bad!")
+
+        schema = self.make_schema()
+        schema.validator = fail
+        form = self.make_form(schema=schema)
+        self.assertEqual(form.get_global_errors(), [])
+        self.request.method = 'POST'
+        self.request.POST = {'foo': 'one', 'bar': 'two'}
+        self.assertFalse(form.validate())
+        self.assertTrue(form.get_global_errors(), ["things are bad!"])
+
     def test_get_field_errors(self):
         schema = self.make_schema()