Sites pane - #20061

Adds a “Sites” pane to element editor sidebars, which replaces the “Status” pane for localized element types on multi-site installs.

The Sites pane:

• Lists the sites the element is saved to that the user can edit, with the current site first (marked with a checkmark). If there are 2+ other sites, they’re listed within an “X other sites” disclosure.
• Links each site name to the element’s edit page in that site. Within element editor slideouts, clicking on a site name switches the slideout to that site instead (saving any pending draft changes first, or confirming that unsaved changes will be lost, for element types that don’t autosave drafts).
• Includes a status toggle for each site, if the element type has per-site statuses.
• Has an “Add a site…” menu for sites the element can be added to. Newly-added sites get a status toggle if the element will be autosaved to them. They also get a button for undoing the selection: for element types that don’t autosave drafts it’s shown right away; otherwise it’s shown once the draft has been autosaved to the site (if the user is allowed to delete the draft for the site), and deletes the draft for that site via elements/delete-for-site. elements/save-draft responses now include a canDeleteForSite key for this.

Unlike the Status pane, all of this is visible without clicking the “…” button first.

Element type support

• craft\base\Element::showSitesField() determines whether the Sites pane should be used in place of the Status pane. By default it’s used for localized elements that support multiple sites, regardless of whether the element type has statuses. Element types that have statuses and override statusFieldHtml() keep the Status pane, so any customizations aren’t lost, and element types can override showSitesField() to opt out.
• Element types without statuses only show the Sites pane when there are sites the element can be added to, or when craft\base\Element::hasCustomPropagation() returns true.
• If sitesFieldHtml() doesn’t return anything (e.g. on single-site installs), the Status pane is shown instead, for element types with statuses.
• The Status pane’s behavior is unchanged.

Also fixes Elements::deleteElementsForSite() not finding provisional drafts in other sites, which caused them to be deleted entirely (e.g. when deleting an element for a site while editing a provisional draft), and lines up sidebar pane headings (“Sites”, “Status”, “Notes about your changes”, etc.) with the labels within the panes.

Related discussions

• Add an option to always expand the site list in the entry sidebar #13982 — the “…” button is too easy to miss; asks for the site list to always be visible
• Add a config setting to make the status field always visible for all the websites in a multi-site setup #19320 — a status toggle was switched off for one site while the entry stayed live on others, because the other sites were hidden
• Better communication of "enabled/disabled" status on multi-site builds #10010 — the per-site status isn’t clear until the “…” button is clicked
• Optional simplification of the the status dialog in the sidebar to only show the active site? #18370 — asks to only show the current site’s status. The suggested .expand-status-btn CSS workaround no longer applies to multi-site entries.
• Please add a way to 1) hide the status switches per site (so it's always in sync) and 2) hide the status switches alltogether #9021 — asks for a way to hide per-site status toggles

Collapsed:

Expanded:

With “Add a site…” button: