This became a problem because #foundation-office:matrix.org has a
malformed create event with its `predecessor` set to a string instead of
a map.
The solution to this is, unfortunately, to do more shotgun parsing to
extract only the desired fields rather than trying to parse the entire
content every time. To prevent this kind of problem from happening
again, `RoomCreateEventContent` must only be used for creating new PDUs,
existing PDUs must be shotgun-parsed.
Previous behavior was causing us to error out of the entire
state_cache::update_membership function when it saw an invalid m.direct,
making it impossible for affected users to join upgraded rooms. This bug
is especially bad if an affected user attempts to upgrade a room,
because we will fail to create their join event in the new room, leaving
both rooms permanently bricked.
The new behavior should never prevent users from joining a room based on
the contents of their account data, and should migrate the `m.direct`
event in a reasonable way even if it is partially corrupted by the
element bug.
This also fixes a bug where the previous implementation will
unintentionally remove any keys that aren't part of the expected
m.direct schema. I don't know of any cases where this came up in
practice.
Fixes: #46
The implementation inside each function is unchanged from the original.
I intend to clean up and fix bugs in later commits, so the diff will be
more clear.
This change is fully automated, except the `rustfmt.toml` changes and
a few clippy directives to allow specific functions with too many lines
because they are longer now.
