Black 23 enforces some slightly more specific rules about empty line
counts and redundant parenthesis removal, but the result is still
compatible with Black 22.
(This does not actually upgrade our Python environment to Black 23
yet.)
Signed-off-by: Anders Kaseorg <anders@zulip.com>
Previously, Attachment.is_realm_public and its cousin,
Attachment.is_web_public, were properties that began as False and
transitioned to True only when a message containing a link to the
attachment was sent to the appropriate class of stream, or such a link
was added as part of editing a message.
This pattern meant that neither field was updated in situations where
the access permissions for a message changed:
* Moving the message to a different stream.
* Changing the permissions for a stream containing links to the message.
This correctness issue has limited security impact, because uploaded
files are secured both by a random URL and by these access checks.
To fix this, we reformulate these fields as a cache, with code paths
that change the permissions affecting an attachment responsible for
setting these values to the `None` (uncached) state. We prefer setting
this `None` state over computing the correct permissions, because the
correct post-edit permissions are a function of all messages
containing the attachment, and we don't want to be responsible for
fetching all of those messages in the edit code paths.
Anders Kaseorg
Tim Abbott