Build meta tags for panels much later like metatag and metatag_views do so they can be altered after page data has been processed

Hi. I use search_api and facetapi to implement a content search view which is displayed on a panel page. Now I need to have pages with certain active facet items to be set to noindex.

The problem is that I can't alter the meta tags because hook_metatag_metatags_view_alter() has already been called from metatag_panels before the facet items are even processed (or can be altered in hook_facet_items_alter()).

Is there a specific reason why metatag_panels builds the metatags so early in metatag_panels_ctools_render_alter() before any hook_page_build() has run?

metatag itself builds them in metatag_page_build() and metatag_views in metatag_views_page_alter() which is much later than metatag_panels does.

My patch moves most of metatag_panels' meta tag creation code from metatag_panels_ctools_render_alter() to metatag_panels_page_build() which allows altering after most hook_page_build()'s have run. Facet items will be processed at that time and I can alter the tags as required.