As a user who performed a very "big" search in maniphest, I want to know how many pages there may be after the first, or ideally the exact number of search results, either for statistics' sake or in order to plan my actions on the results accordingly.
Cf. https://phabricator.wikimedia.org/maniphest/query/rtD5OXOlaUbe/#R which probably has tens of thousands results, or maybe thousands, but I have no idea.
Because the visibility of each result depends on policies that can only be evaluated in the application, providing an exact count is very expensive, and providing an approximate count may disclose sensitive information. See https://secure.phabricator.com/T13133 for some more discussion of pagination and "overheating" (when queries fail early after filtering too many results).
Although it would be nice to provide an exact or approximate count, I don't see a way to do it without making most queries query dramatically more expensive, or sometimes disclosing information the viewer does not have permission to access, so I don't currently anticipate ever providing this functionality in the upstream.
Thanks for the detailed explanation!
Declining this task as the costs (given the architecture) seem to outweigh the benefits and as we don't plan to write/maintain downstream code changes either.