Apply full_clean on save_revision and preview

This requires us to set fake (but realistic) values for 'path' and 'depth' during preview_on_create
in order to pass validation.

wagtail/wagtailadmin/views/pages.py

@@ -388,6 +388,7 @@ def preview_on_edit(request, page_id):
 
     if form.is_valid():
         form.save(commit=False)
+        page.full_clean()
 
         preview_mode = request.GET.get('mode', page.default_preview_mode)
         response = page.serve_preview(page.dummy_request(), preview_mode)
@@ -426,9 +427,19 @@ def preview_on_create(request, content_type_app_name, content_type_model_name, p
     if form.is_valid():
         form.save(commit=False)
 
+        # We need to populate treebeard's path / depth fields in order to pass validation.
+        # We can't make these 100% consistent with the rest of the tree without making actual
+        # database changes (such as incrementing the parent's numchild field), but by
+        # calling treebeard's internal _get_path method, we can set a 'realistic' value that
+        # will hopefully enable tree traversal operations to at least partially work.
+        page.depth = parent_page.depth + 1
+        page.path = page._get_path(parent_page.path, page.depth, parent_page.numchild + 1)
+
         # ensure that our unsaved page instance has a suitable url set
         page.set_url_path(parent_page)
 
+        page.full_clean()
+
         # Set treebeard attributes
         page.depth = parent_page.depth + 1
         page.path = Page._get_children_path_interval(parent_page.path)[1]

wagtail/wagtailcore/models.py

@@ -604,6 +604,8 @@ class Page(six.with_metaclass(PageBase, MP_Node, ClusterableModel, index.Indexed
                 raise Http404
 
     def save_revision(self, user=None, submitted_for_moderation=False, approved_go_live_at=None, changed=True):
+        self.full_clean()
+
         # Create revision
         revision = self.revisions.create(
             content_json=self.to_json(),