Fixes bug described in d3e4ac7c17 (commitcomment-39049351)
When dealing with searches, there are several variables we have to keep
in mind:
* Whether tag aliases should be applied.
* Whether search terms should be sorted.
* Whether the rating:s and -status:deleted metatags should be added by
safe mode and the hide deleted posts setting.
Which of these things we need to do depends on the context:
* We want to apply aliases when actually doing the search, calculating
the count, looking up the wiki excerpt, recording missed/popular
searches in Reportbooru, and calculating related tags for the sidebar,
but not when displaying the raw search as typed by the user (for
example, in the page title or in the tag search box).
* We want to sort the search when calculating cache keys for fast_count
or related tags, and when recording missed/popular searches, but not
in the page title or when displaying the raw search.
* We want to add rating:s and -status:deleted when performing the
search, calculating the count, or recording missed/popular searches,
but not when calculating related tags for the sidebar, or when
displaying the page title or raw search.
Here we introduce normalized_query and try to use it in contexts where
query normalization is necessary. When to use the normalized query
versus the raw unnormalized query is still subtle and prone to error.
* Refactor fast_count to return nil instead of 1,000,000 if the exact count times out.
* Remove the estimate_post_counts and blank_tag_search_fast_count global config options.
* Replace the hardcoded post count estimates inside fast_count with a
method that parses Postgres's estimated row count from EXPLAIN.
* /counts/posts.json:
** Remove the `raise_on_timeout` parameter.
** Add an `estimate_count=<true|false>` parameter.
** Return null instead of 1,000,000 if the exact count times out.
When doing a tag search, we have to be careful about which user we're
running the search as because the results depend on the current user.
Specifically, things like private favorites, private favorite groups,
post votes, saved searches, and flagger names depend on the user's
permissions, and whether non-safe or deleted posts are filtered out
depend on whether the user has safe mode on or the hide deleted posts
setting enabled.
* Refactor internal searches to explicitly state whether they're
running as the system user (DanbooruBot) or as the current user.
* Explicitly pass in the current user to PostQueryBuilder instead of
implicitly relying on the CurrentUser global.
* Get rid of CurrentUser.admin_mode? (used to ignore the hide deleted
post setting) and CurrentUser.without_safe_mode (used to ignore safe
mode).
* Change the /counts/posts.json endpoint to ignore safe mode and the
hide deleted posts settings when counting posts.
* Fix searches not correctly overriding the hide deleted posts setting
when multiple status: metatags were used (e.g. `status:banned status:active`)
* Fix fast_count not respecting the hide deleted posts setting when the
status:banned metatag was used.
