Widget Customizer: Fade out sidebar sections that lack any rendered widgets

[westonruter]

Currently when there is a widget that is not rendered in the current URL being previewed (e.g. via Widget Visibility), the widget control in the customizer will become semi-transparent to indicate it is not being rendered. The same semi-transparent indicator would be useful for sidebars that are empty or which lack any rendered widgets.

Originally reported in ​https://github.com/x-team/wp-widget-customizer/issues/76

[ocean90]

Probably a wontfix because of #27406.

[westonruter]

Actually, I think this ticket and #27406 are complimentary. Widget areas not rendered at the currently-previewed URL could either be hidden altogether (as they are now) or they can be shown but faded out (as unrendered widgets are now). Additionally, a widget area may very well be used in a template (it has a dynamic_sidebar() call) but all of the widgets inside of it may be hidden due to Widget Visibility rules; in this case, it would be also useful for the widget area to be marked in a way that indicates you can't currently see the widget area in the preview as currently-configured.

Also as mentioned on #27406:

There could also be a checkbox/button to toggle between showing only the widget areas currently used in the previewed URL, or to show all of the widget areas regardless but with some additional indicator

[westonruter]

See also #40432 (Customizer: Should we stop contextually hiding features?)