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Changes between Version 3 and Version 4 of Ticket #53816

v3	v4
5	5	There are a few problems there:
6	6
7		* We have multiple, closely related global variables (`$sidebars_widgets`+`$_wp_sidebars_widgets`, ~~also~~ `$wp_registered_widgets`, `$wp_registered_sidebars`). If we update one, we should also update the others for consistency. Sometimes we don't and we run into [https://github.com/WordPress/gutenberg/issues/33335#issuecomment-879903958 undefined behaviors].
	7	* We have multiple, closely related global variables (`$sidebars_widgets`+`$_wp_sidebars_widgets`, `$wp_registered_widgets`, `$wp_registered_sidebars`). If we update one, we should also update the others for consistency. Sometimes we don't and we run into [https://github.com/WordPress/gutenberg/issues/33335#issuecomment-879903958 undefined behaviors].
8	8	* We use a function called `retrieve_widgets` as a mean to fix any discrepancies in the stored sidebar-to-widget mapping. It's called `retrieve`, but it actually does some writing. This is a source of confusion in itself so I [https://core.trac.wordpress.org/ticket/53811 proposed renaming it].
9	9	* We [https://github.com/WordPress/wordpress-develop/pull/1433 we have to call retrieve_widgets in GET API endpoints] which makes it read-write, not read-only. This breaks HTTP caching and is also a [https://github.com/WordPress/gutenberg/issues/33335#issuecomment-879903958 source of bugs].