Introduce a flag to indicate a "fresh site"

[helen]

Closely tied to starter content in #38114, but also potentially generally useful.

Thinking a flag (option) that is set on install and then deleted upon the first run of one of a number of actions. Those actions should be: adding/updating a post or page, changing widgets, or saving customizer settings.

[swissspidy]

It might make more sense to have different options for each action to target the user better. They could open the customizer and hit save, but still be a newbie in regard to saving posts and widgets.

[ocean90]

38533.1.diff​ sets the option to 0 so the option is autoloaded to prevent further db queries.

Not sure about the get_option() in default-filters though, looks like it's first one that runs so early. Currently it's wp_plugin_directory_constants() with get_option('siteurl') so I guess it's fine.

[westonruter]

Please review and make additional revs via pushing to feature branch on GitHub. See PR: ​https://github.com/xwp/wordpress-develop/pull/188

[westonruter]

In 38991:

Customize: Introduce starter content and site freshness state.

A theme can opt-in for tailored starter content to apply to the customizer when previewing the theme on a fresh install, when fresh_site is at its initial 1 value. Starter content is staged in the customizer and does not go live unless the changes are published. Initial starter content is added to Twenty Seventeen.

• The fresh_site flag is cleared when a published post or page is saved, when widgets are modified, or when the customizer state is saved.
• Starter content is registered via starter-content theme support, where the argument is an array containing widgets, posts, nav_menus, options, and theme_mods. Posts/pages in starter content are created with the auto-draft status, re-using the page/post stubs feature added to nav menus and the static front page controls.
• A get_theme_starter_content filter allows for plugins to extend a theme's starter content.
• Starter content in themes can/should re-use existing starter content items in core by using named placeholders.
• Import theme starter content into customized state when fresh site.
• Prevent original_title differences from causing refreshes if title is present.
• Ensure nav menu item url is set according to object when previewing.
• Make sure initial saved state is false if there are dirty settings without an existing changeset.
• Ensure dirty settings are cleaned upon changeset publishing.

Props helen, westonruter, ocean90.
Fixes #38114, #38533.

[helen]

Looks like this is getting populated as 1 on existing sites, I guess we should populate as 0 in that case.

[westonruter]

OK, so populate_options() will populate the options defined when upgrading in addition to when installing. Maybe the fresh_site flag should be set in wp_install() instead. This would ensure it only gets added for new installs and only once.

See 38533.2.diff​.

[helen]

In 39076:

Only set fresh_site during an actual fresh install.

props westonruter.
fixes #38533.

[ocean90]

#38552 was marked as a duplicate.

[westonruter]

In 39276:

Customize: Add unit tests for importing theme starter content.

Props welcher, westonruter.
See #38114, #38533, #38615.
Fixes #38540.

[westonruter]

In 40608:

Customize: Fix clearing of fresh_site option flag when editing sidebars on widgets admin screen.

Amends [38991].
See #38114, #38533.
Fixes #40722.