There is no need to fetch the entire Stream or UserProfile objects, as
only several fields are needed. We use Django's .values() method to only
get what's needed.
For UserProfiles, it means that we get from the queries are dictionaries
already in the display_recipient form (UserDisplayRecipient type) - so
we can remove the user_profile_to_display_recipient_dict function, as
there's no need for this UserProfile -> UserDisplayRecipient conversion
anymore.
Instead of having the rather unclear type Union[str,
List[UserDisplayRecipient]] where display_recipient of message dicts was
involved, we use DisplayRecipientT (renamed from DisplayRecipientCacheT
- since there wasn't much reason to have the word Cache in there), which
makes it clearer what is the actual nature of the objects and gets rid
of this pretty big type declaration.
Since the display_recipients dictionaries corresponding to users are
always dictionaries with keys email, full_name, short_name, id,
is_mirror_dummy - instead of using the overly general Dict[str, Any]
type, we can define a UserDisplayRecipient type,
using an appropriate TypedDict.
The type definitions are moved from display_recipient.py to types.py, so
that they can be imported in models.py.
Appropriate type adjustments are made in various places in the code
where we operate on display_recipients.
The user information in display_recipient in cached message_dicts
becomes outdated if the information is changed in any way.
In particular, since we don't have a way to find all the message
objects that might contain PMs after an organization toggles the
setting to hide user email addresses from other users, we had a
situation where client might see inaccurate cached data from before
the transition for a period of up to hours.
We address this by using our generic_bulk_cached_fetch toolchain to
ensure we always are fetching display_recipient data from the database
(and/or a special recipient_id -> display_recipient cache, which we
can flush easily).
Fixes#12818.
Tim Abbott
Mateusz Mandera