Render the HTML for autocomplete results server-side instead of in
Javascript. This is cleaner than building HTML in Javascript, but it may
hurt caching because the HTTP responses are larger.
Fixes#4698: user autocomplete contains links to /posts
Also fixes a bug where tag counts in the autocomplete menu were different
from tag counts displayed elsewhere because of differences in rounding.
The previous cache policy was that all autocomplete results were cached
for a fixed 7 days. The new policy is that if autocomplete returns more
than 10 results they're cached for 24 hours, otherwise if it returns
less than 10 results they're cached for 1 hour.
The rationale is that if autocomplete returns a lot of results, then the
top 10 results are relatively stable and unlikely to change, but if it
returns less than 10 results, then the results are unstable and can be
easily changed.
We also change it so that autocomplete calls can be cached publicly.
Public caching means that HTTP requests are cached by Cloudflare. This
will ideally reduce load on the server and reduce latency for end users.
This is only safe for calls that return the same results for all users
(i.e. the results don't depend on the current user), since the cache is
publicly shared by all users. Currently username, favgroup, and saved
search autocomplete results depend on the current user, so they can't be
publicly cached.
This refactors the autocomplete Javascript to use a single dedicated
/autocomplete.json endpoint instead of a bunch of separate endpoints.
This simplifies the autocomplete Javascript by making it so that instead
of calling a different endpoint for each type of query (for users, wiki
pages, pools, artists, etc), then having to parse the results of each
call to get the data we need, we can call a single endpoint that returns
exactly what we need.
This also means we don't have to parse searches clientside in order to
autocomplete metatags. Instead we can just pass the search term to the
server and let it parse the search, which is easy to do serverside.
Finally, this makes autocomplete easier to test, and it makes it easier
to add more sophisticated autocomplete behavior, since most of the logic
lives serverside.
