synapse fails to start under Twisted >= 18.4

[richvdh]

Looks like we are relying on a private identifier which has been removed in Twisted 18.4:

Traceback (most recent call last):
  File "/usr/lib/python2.7/runpy.py", line 174, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/home/rav/work/synapse/synapse/app/homeserver.py", line 31, in <module>
    from synapse.crypto import context_factory
  File "synapse/crypto/context_factory.py", line 17, in <module>
    from twisted.internet._sslverify import _OpenSSLECCurve, _defaultCurveName
ImportError: cannot import name _OpenSSLECCurve

[irstevenson]

This just bit me with doing the upgrade to 0.28.0. To fix it, I had to do the following in my virtual env:

pip install -U "Twisted<18.4"

Just in case anyone else running a HS gets stuck until the fix is released.

[richvdh]

For clarification, this is unrelated to synapse 0.28. The problem has been there since the very first versions of synapse.

[Half-Shot]

Happy to close now?