1382992 - Figure out what do to with canDrop() with respect to sync vs async

Status: NEW

(Firefox :: Bookmarks & History, enhancement, P3)

Description

[Marco Bonardo [:mak]]

canDrop is synchronous. It currently checks that we don't drop a container inside itself or a descendant container and to do that it has to walk the container hierarchy by doing main-thread I/O.

Collecting the information on drag start is also not possible, because dragstart is a synchronous operation where we must synchronously fill the dataTransfer (there's some ongoing work to make this async but no ETA).

Comment 1

[Marco Bonardo [:mak]]

we could keep an up-to-date bookmarks hierarchy in a memory cache. The main issue would be a synchronous request before the cache has been populated, for which we could retain a synchronous fallback, or throw and let the consumer take the more pessimistic fallback.