Customize: Starter content does not play nicely with drafted changes

[dlh]

Open the customizer on a "fresh site" running twenty seventeen, and save your changes as a draft. each time you load the draft in the customizer after that, the starter content will be re-imported as new drafts. when the changeset is published, each copy of the imported starter content is published.

[westonruter]

​https://github.com/xwp/wordpress-develop/pull/298

[westonruter]

@dlh I have an initial patch which seems to fix the issue. See 42395.0.wip.diff​. But it's not pretty. I'd appreciate your insights.

I'm not satisfied with the patch I have, as it is hacky and exposes some underlying problems with how we implemented settings for nav menus and nav menu items. In particular, we're including dynamic “generated” properties like original_title and type_label in the changeset value. These should be omitted and only dynamically added when the via the filter wp_setup_nav_menu_item, for example.

[dlh]

Could we assume that a non auto-draft changeset no longer needs starter content imported, as sketched in 42395.diff​?

[westonruter]

@dlh That's a great point. I was retaining the importing of starter content because I was thinking of the case where a user switches to a different theme that has starter content. But if you've saved a draft then you wouldn't be able to switch themes anymore anyway.

[joemcgill]

Nice and clean. +1

[obenland]

Was able to reproduce and 42395.3.diff​ looks like a fine fix. 👍

[westonruter]

In 42107:

Customize: Prevent re-importing starter content when changeset is saved as draft or scheduled.

Themes cannot currently be switched in Customizer after changeset is saved anyway.

Props dlh, westonruter.
See #40146, #42411, #42126.
Fixes #42395.