f0c680e9c0 introduced a call to
message_helper.process_new_message without first calling
message_store.set_message_flags on the message.
This resulted in it being possible as a race, when loading the Zulip
app to a stream/topic/near narrow, for a message to have the
`historical` flag be undefined due to not being initialized.
That invalid state, in turn, resulted in the message_list_view code
path for rendering the message feed incorrectly displaying additional
recipient bars around the message.
We could fix this by just calling message_store.set_message_booleans
in this code path. However, this bug exposes the fact that it's very
fragile to expect every code path to call that function before
message_helper.process_new_message.
So we instead fix this by moving message_store.set_message_booleans
inside message_helper.process_new_message.
One call point of concern in this change is maybe_add_narrow_messages,
which could theoretically reintroduce the double set_message_flags
bugs detailed in 9729b1a4ad. However, I
believe that to not be possible, because that call should never
experience a cache miss.
The other existing code paths were already calling
set_message_booleans immediately before
message_helper.process_new_message. They are still changing here, in
that we now do a cache lookup before attempting to call
set_message_booleans. Because the message booleans do not affect the
cache lookup and the local message object is discarded in case of a
cache hit, this should have no functional impact.
Because I found the existing comment at that call site confusing and
almost proposed removing it as pointless, extend the block comment to
explicitly mention that the purpose is refreshing our object.
Fixes#21503.
0d90bb2569