The order of nested InlinePanels (recently formally added in 5566)
doesn't get saved properly due to some now-invalid assumptions in the JS
selector code.
Currently, Wagtail users can use the editor up/down arrows to order
InlinePanel elements that contain child InlinePanels, but these may not
be properly saved.
Before InlinePanel nesting was supported, it was a safer bet that a
child panel would only contain one hidden input named "-ORDER". With
nesting, however, a parent panel will also contain hidden inputs named
like this for its child panels. This breaks the logic used in the
ordering code.
This change modifies the logic to use the jQuery `.children()` selector
instead of `.next()`, ensuring that we reference the correct adjacent
panel item.
An easy way to test this against current master is to use the Wagtail
testapp test models that exercise this behavior:
1. `wagtail start testwagtail` to create a new project.
2. `cd testwagtail`
3. Edit testwagtail/settings/base.py to add the Wagtail test
application `'wagtail.tests.testapp'` to the list of `INSTALLED_APPS`.
For the admin to work properly with this app, you also need to add
`'wagtail.contrib.settings'` to that list and copy the definition of
`WAGTAILADMIN_RICH_TEXT_EDITORS` from wagtail/tests/settings.py.
4. `./manage.py migrate` to create your local database.
5. `./manage.py createsuperuser` to create an admin user.
6. Create a new Event Page
(http://localhost:8000/admin/pages/add/tests/eventpage/3/).
7. Fill in all required items, and then add multiple speakers under
"Speaker Lineup". For each speaker, add at least one Award. Save the
page.
8. Try using the up/down arrows to reorder the speakers (the parent
InlinePanel), and save the page.
9. Note that when the page reloads, the ordering hasn't been saved. If
you debug using the developer tools, you'll notice that this is because
the code being modified here selects the child panel items instead of
the adjacent parent panel item.
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