Render help text for structblocks

wagtail/wagtailadmin/templates/wagtailadmin/block_forms/struct.html

@@ -1,4 +1,7 @@
 <div class="struct-block">
+    {% if help_text %}
+        <div class="object-help help">{{ help_text }}</div>
+    {% endif %}
     <ul>
         {% for child in bound_child_blocks %}
             <li>

wagtail/wagtailcore/blocks/struct_block.py

@@ -79,7 +79,8 @@ class BaseStructBlock(Block):
         ]
 
         return render_to_string('wagtailadmin/block_forms/struct.html', {
-            'bound_child_blocks': bound_child_blocks
+            'bound_child_blocks': bound_child_blocks,
+            'help_text': getattr(self.meta, 'help_text', None),
         })
 
     def value_from_datadict(self, data, files, prefix):

wagtail/wagtailcore/tests/test_blocks.py

@@ -560,6 +560,31 @@ class TestStructBlock(unittest.TestCase):
         self.assertIn('<input id="mylink-title" name="mylink-title" placeholder="Title" type="text" value="Torchbox" />', html)
         self.assertIn('<input id="mylink-link" name="mylink-link" placeholder="Link" type="url" value="http://www.torchbox.com" />', html)
 
+    def test_render_form_with_help_text(self):
+        class LinkBlock(blocks.StructBlock):
+            title = blocks.CharBlock()
+            link = blocks.URLBlock()
+
+            class Meta:
+                help_text = "Self-promotion is encouraged"
+
+        block = LinkBlock()
+        html = block.render_form({
+            'title': "Wagtail site",
+            'link': 'http://www.wagtail.io',
+        }, prefix='mylink')
+
+        self.assertIn('<div class="object-help help">Self-promotion is encouraged</div>', html)
+
+        # check it can be overridden in the block constructor
+        block = LinkBlock(help_text="Self-promotion is discouraged")
+        html = block.render_form({
+            'title': "Wagtail site",
+            'link': 'http://www.wagtail.io',
+        }, prefix='mylink')
+
+        self.assertIn('<div class="object-help help">Self-promotion is discouraged</div>', html)
+
     def test_media_inheritance(self):
         class ScriptedCharBlock(blocks.CharBlock):
             media = forms.Media(js=['scripted_char_block.js'])