We were using Google's diff-match-patch library to diff HTML. The
problem with that approach is that it is a text differ, not an HTML
differ and so it ends up messing up the HTML tags. `lxml` is a safer
option.
Fixes: #7219.
Rationale: For the more off-to-the-side edit history view, changes
are easier to digest by highlighting deleted content in red followed
immediately by added and changed content in green.
TODO: Toggle for showing the edited messages without highlighting;
deleted content would not be shown in this view.
A lot of care has been taken to ensure we're using the realm that the
message is being sent into, not the realm of the sender, to correctly
handle the logic for cross-realm bot users such as the notifications
bot.
This needs to be deployed to both staging and prod at the same
off-peak time (and the schema migration run).
At the time it is deployed, we need to make a few changes directly in
the database:
(1) UPDATE django_content_type set app_label='zerver' where app_label='zephyr';
(2) UPDATE south_migrationhistory set app_name='zerver' where app_name='zephyr';
(imported from commit eb3fd719571740189514ef0b884738cb30df1320)
Tim Abbott
rht
Harshit Bansal
Jack Zhang
Konstantin Gukov
Aditya Bansal
Raghav Jajodia
Robert Hönig
Sahil Dua
Eklavya Sharma
medullaskyline
Leo Franchi
Luke Faraone
Tim Abbott