the email pusher is broken in 0.33.7

[richvdh]

If you leave email_templates unset, or set to res/templates, you get the following error when the pusher tries to send an email:

Traceback (most recent call last):
  File synapse/push/emailpusher.py, line 125, in _process
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/internet/defer.py, line 1416, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/python/failure.py, line 491, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File synapse/push/emailpusher.py, line 177, in _unsafe_process
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/internet/defer.py, line 1416, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/python/failure.py, line 491, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File synapse/push/emailpusher.py, line 287, in send_notification
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/internet/defer.py, line 1418, in _inlineCallbacks
    result = g.send(result)
  File synapse/push/mailer.py, line 178, in send_notification_mail
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/jinja2/environment.py, line 1008, in render
    return self.environment.handle_exception(exc_info, True)
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/jinja2/environment.py, line 780, in handle_exception
    reraise(exc_type, exc_value, tb)
  File synapse/res/templates/notif_mail.html, line 5, in top-level template code
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/jinja2/loaders.py, line 235, in get_source
    raise TemplateNotFound(template)
TemplateNotFound: mail.css

[richvdh]

A workaround for now is to explicitly set email_templates to the full path of wherever synapse/res/templates is on your system.

[richvdh]

This was introduced by #4052.

So, some backstory is necessary here:

The default config (before #4052) gave an example setting of res/templates for email_templates. However, this never worked, because synapse changes directory to / once it starts (at least if it is run with the --daemonize arg, as synctl does). In practice therefore, anyone who uses email notifications will have set email_templates to an absolute path.

In #4052, I had the great idea of solving #4014 and matrix-org/package-synapse-debian#37 by including the example templates as package data, and using them from there if email_templates was unset (or, in an attempt to preserve backwards-compatibility, if it was set to res/templates - not that that will have helped anyone in practice, as per the above).

However, it turns out that attempting to load the email templates from the package data has exactly the same problem as loading them from a relative path: the supporting templates like mail.css can't be found once synapse changes directory.

[richvdh]

fixed by #4069