Mail: Include a filtering searchbar in folder select dialog
I use this dialog quite often to move selected mails (or other things) across accounts, to a specific folder, without the imprecision and risk of drag-and-drop, or having to search through my gazillion IMAP folders:
It is very convenient for me. However, while GTK's "typeahead" search kinda works, I would find it even more convenient to also have the ability to do a view filtering search, i.e. where only the matches get shown, so that I don't have to scroll nor visually process a bunch of rows.
My recommendation would be to have, just above that treeview widget in that dialog, a GtkSearchEntry, where I could just type a string in there and the relevant targets for each account would appear (it would need to still show me the expander widgets to tell from which account each search result comes from, though). Not only would this be more discoverable, but it would be much faster for me.
Whatsmore, with the reduced scrolling this would represent, I could imagine that this could open up the opportunity to have the "Move" action be part of the headerbar toolbar where a GtkPopover (with the searchentry included) could emanate from... eventually after @gnumdk's work in #961 (closed). Or maybe it could be done as a plugin, even.