Teach StreamBlocks about NON_FIELD_ERRORS

A StreamBlock can now have NON_FIELD_ERRORS as part of its error dict.
These will be displayed as error messages above the StreamBlock in the
admin upon form submission.

No code in Wagtail currently makes use of this feautre. It is available
for developers of sites to use in their custom StreamField blocks.

wagtail/wagtailadmin/templates/wagtailadmin/block_forms/sequence.html

@@ -14,8 +14,15 @@
 {% endcomment %}
 <div class="sequence-container sequence-type-{% block sequence_type_class %}{% endblock %}">
     <input type="hidden" name="{{ prefix }}-count" id="{{ prefix }}-count" value="{{ list_members_html|length }}">
-    
+
     {% block header %}{% endblock %}
+
+    {% if block_errors %}
+        {% for error in block_errors %}
+            <div class="help-block help-critical">{{ error }}</div>
+        {% endfor %}
+    {% endif %}
+
     <div class="sequence-container-inner">
         <ul id="{{ prefix }}-list" class="sequence">
             {% for list_member_html in list_members_html %}

wagtail/wagtailcore/blocks/stream_block.py

@@ -3,7 +3,7 @@ from __future__ import absolute_import, unicode_literals
 import collections
 
 from django import forms
-from django.core.exceptions import ValidationError
+from django.core.exceptions import NON_FIELD_ERRORS, ValidationError
 from django.forms.utils import ErrorList
 from django.template.loader import render_to_string
 from django.utils.encoding import python_2_unicode_compatible, force_text
@@ -130,6 +130,7 @@ class BaseStreamBlock(Block):
             'list_members_html': list_members_html,
             'child_blocks': self.child_blocks.values(),
             'header_menu_prefix': '%s-before' % prefix,
+            'block_errors': error_dict.get(NON_FIELD_ERRORS),
         })
 
     def value_from_datadict(self, data, files, prefix):

wagtail/wagtailcore/tests/test_blocks.py

@@ -5,7 +5,7 @@ import unittest
 
 from django import forms
 from django.forms.utils import ErrorList
-from django.core.exceptions import ValidationError
+from django.core.exceptions import NON_FIELD_ERRORS, ValidationError
 from django.test import TestCase, SimpleTestCase
 from django.utils.safestring import mark_safe, SafeData
 
@@ -18,6 +18,36 @@ from wagtail.tests.testapp.blocks import SectionBlock
 import base64
 
 
+class IntegerBlock(blocks.CharBlock):
+    def clean(self, value):
+        out = super(IntegerBlock, self).clean(value)
+        try:
+            return int(out)
+        except ValueError:
+            raise ValidationError('Value must be an integer')
+
+
+class ColumnBlock(blocks.StructBlock):
+    width = IntegerBlock()
+    content = blocks.TextBlock()
+
+
+class ValidatedBlock(blocks.StreamBlock):
+    column = ColumnBlock()
+    required_width = 6
+
+    def clean(self, value):
+        blocks = super(ValidatedBlock, self).clean(value)
+        width = sum(block.value['width'] for block in blocks)
+        if width != self.required_width:
+            error = 'You must have exactly %d columns, not %d' % (
+                self.required_width, width)
+            raise ValidationError('Validation error in StreamBlock', params={
+                NON_FIELD_ERRORS: [error],
+            })
+        return blocks
+
+
 class TestFieldBlock(unittest.TestCase):
     def test_charfield_render(self):
         block = blocks.CharBlock()
@@ -1039,7 +1069,7 @@ class TestListBlock(unittest.TestCase):
         self.assertIn('value="chocolate"', form_html)
 
 
-class TestStreamBlock(unittest.TestCase):
+class TestStreamBlock(SimpleTestCase):
     def test_initialisation(self):
         block = blocks.StreamBlock([
             ('heading', blocks.CharBlock()),
@@ -1271,6 +1301,71 @@ class TestStreamBlock(unittest.TestCase):
             3: ['Enter a valid URL.'],
         })
 
+    def test_block_level_validation_no_errors(self):
+        block = ValidatedBlock()
+
+        post_data = {'columns-count': '3'}
+        for i in range(3):
+            post_data.update({
+                'columns-%d-deleted' % i: '',
+                'columns-%d-order' % i: str(i),
+                'columns-%d-type' % i: 'column',
+                'columns-%d-value-width' % i: str(i + 1),
+                'columns-%d-value-content' % i: 'hello %d' % (i,),
+            })
+
+        block_value = block.value_from_datadict(post_data, {}, 'columns')
+        try:
+            block.clean(block_value)
+        except ValidationError:
+            self.fail('Should have passed validation')
+
+    def test_block_level_validation_throws_errors(self):
+        block = ValidatedBlock()
+
+        post_data = {'columns-count': '4'}
+        for i in range(4):
+            post_data.update({
+                'columns-%d-deleted' % i: '',
+                'columns-%d-order' % i: str(i),
+                'columns-%d-type' % i: 'column',
+                'columns-%d-value-width' % i: '2',
+                'columns-%d-value-content' % i: 'hello %d' % (i,),
+            })
+
+        block_value = block.value_from_datadict(post_data, {}, 'columns')
+        with self.assertRaises(ValidationError) as catcher:
+            block.clean(block_value)
+
+        self.assertEqual(catcher.exception.params, {
+            NON_FIELD_ERRORS: ['You must have exactly 6 columns, not 8'],
+        })
+
+    def test_block_level_validation_renders_errors(self):
+        block = ValidatedBlock()
+
+        post_data = {'columns-count': '2'}
+        for i in range(2):
+            post_data.update({
+                'columns-%d-deleted' % i: '',
+                'columns-%d-order' % i: str(i),
+                'columns-%d-type' % i: 'column',
+                'columns-%d-value-width' % i: str(i + 2),
+                'columns-%d-value-content' % i: 'hello %d' % (i,),
+            })
+
+        block_value = block.value_from_datadict(post_data, {}, 'columns')
+        error_message = 'You must have exactly 6 columns, not 5'
+        errors = ErrorList([
+            ValidationError('Validation error in StructBlock', params={
+                NON_FIELD_ERRORS: [error_message]
+            })
+        ])
+
+        self.assertInHTML(
+            '<div class="help-block help-critical">%s</div>' % (error_message,),
+            block.render_form(block_value, prefix='columns', errors=errors))
+
     def test_html_declarations(self):
         class ArticleBlock(blocks.StreamBlock):
             heading = blocks.CharBlock()