Add the `alters_data` attribute on `Page.copy()`.

This makes sure the variable can't be printed in the template,
performing an accidental copy of the page. That also happened when using
the `{% print %}` tag from my django-debugtools package

CHANGELOG.txt

@@ -33,6 +33,7 @@ Changelog
  * Fix: `search_garbage_collect` management command now works when wagtailsearchpromotions is not installed (Morgan Aubert)
  * Fix: `wagtail.contrib.settings` context processor no longer fails when `request.site` is unavailable (Diederik van der Boor)
  * Fix: `TableBlock` content is now indexed for search (Morgan Aubert)
+ * Fix: `Page.copy()` is now marked as `alters_data`, to prevent template code from triggering it (Diederik van der Boor)
 
 
 1.7 (20.10.2016)

docs/releases/1.8.rst

@@ -64,6 +64,7 @@ Bug fixes
  * ``search_garbage_collect`` management command now works when wagtailsearchpromotions is not installed (Morgan Aubert)
  * ``wagtail.contrib.settings`` context processor no longer fails when ``request.site`` is unavailable (Diederik van der Boor)
  * ``TableBlock`` content is now indexed for search (Morgan Aubert)
+ * Fix: ``Page.copy()`` is now marked as ``alters_data``, to prevent template code from triggering it (Diederik van der Boor)
 
 
 Upgrade considerations

wagtail/wagtailcore/models.py

@@ -1182,6 +1182,8 @@ class Page(six.with_metaclass(PageBase, AbstractPage, index.Indexed, Clusterable
 
         return page_copy
 
+    copy.alters_data = True
+
     def permissions_for_user(self, user):
         """
         Return a PagePermissionsTester object defining what actions the user can perform on this page