Introduce id_for_label method on Block

wagtail/wagtailadmin/templates/wagtailadmin/block_forms/field.html

@@ -1,6 +1,8 @@
 {% load wagtailadmin_tags %}
 <div class="field {{ field|fieldtype }} widget-{{ field|widgettype }}{% if name %} fieldname-{{ name }}{% endif %}{% if classes %} {{ classes }}{% endif %}{% if errors %} error{% endif %}">
-    {{ label_tag }}
+    {% if label %}
+        <label{% if id_for_label %} for="{{ id_for_label }}"{% endif %}>{{ label }}</label>
+    {% endif %}
     <div class="field-content">
         <div class="input">
             {{ widget }}

wagtail/wagtailcore/blocks/base.py

@@ -272,6 +272,13 @@ class Block(six.with_metaclass(BaseBlock, object)):
 
         return errors
 
+    def id_for_label(self, prefix):
+        """
+        Return the ID to be used as the 'for' attribute of <label> elements that refer to this block,
+        when the given field prefix is in use. Return None if no 'for' attribute should be used.
+        """
+        return None
+
     def deconstruct(self):
         # adapted from django.utils.deconstruct.deconstructible
         module_name = self.__module__

wagtail/wagtailcore/blocks/field_block.py

@@ -22,17 +22,12 @@ class FieldBlock(Block):
     class Meta:
         default = None
 
+    def id_for_label(self, prefix):
+        return self.field.widget.id_for_label(prefix)
+
     def render_form(self, value, prefix='', errors=None):
         widget = self.field.widget
 
-        if self.label:
-            label_html = format_html(
-                """<label for={label_id}>{label}</label> """,
-                label_id=widget.id_for_label(prefix), label=self.label
-            )
-        else:
-            label_html = ''
-
         widget_attrs = {'id': prefix, 'placeholder': self.label}
 
         field_value = self.value_for_form(value)
@@ -47,9 +42,9 @@ class FieldBlock(Block):
         return render_to_string('wagtailadmin/block_forms/field.html', {
             'name': self.name,
             'label': self.label,
+            'id_for_label': self.id_for_label(prefix),
             'classes': self.meta.classname,
             'widget': widget_html,
-            'label_tag': label_html,
             'field': self.field,
             'errors': errors if (not widget_has_rendered_errors) else None
         })

wagtail/wagtailcore/tests/test_blocks.py

@@ -733,8 +733,8 @@ class TestListBlock(unittest.TestCase):
     def test_render_form_labels(self):
         html = self.render_form()
 
-        self.assertIn('<label for=links-0-value-title>Title</label>', html)
-        self.assertIn('<label for=links-0-value-link>Link</label>', html)
+        self.assertIn('<label for="links-0-value-title">Title</label>', html)
+        self.assertIn('<label for="links-0-value-link">Link</label>', html)
 
     def test_render_form_values(self):
         html = self.render_form()