For certain queries where both include_history and
use_first_unread_anchor are set to True, we were excluding
historical rows. Now we only use the use_first_unread_anchor
flag to filter rows that we use to find the anchor, without
having it filter the actual search results.
The bug went unreported for a long time, because it only
affected mobile users who had newly subscribed to streams.
Note that we make a small change to the test called
test_use_first_unread_anchor_with_muted_topics, which has
a very scary comment about being "arcane" and "be
absolutely sure you know what you're doing." I think it's
fine.
Also, the new test code would fail before this fix, so it
should help prevent future regressions.
Fixes#8958
36844418e9