Patchwork 3: potential feature removals

[Daniel Axtens]

Hi all,

Patchwork is currently quite complex. This is adding to the bug surface
and impacting reliablity - which as the recent issues have
reinforced, is a fundamental feature for our users.

Patchwork is also maintained by a small, loosely-coordinated team of
unpaid volunteers, and this stuff is increasing the maintenance burden,
making working on patchwork more difficult and significantly more
unpleasant.

I'm considering the following for the next major version of Patchwork -
basically what will come after 2.n bug and stability fixes. Semantic
versioning requires me to call it Patchwork 3, even though I expect
user-facing changes to be very small compared to the 1->2 change. I'm
looking at a timeline of the tail end of this year, but being patchwork,
who knows when it'll eventually happen.

Please let me know if anything is particularly of concern or interest to
you. 

 1) Support Django 2.0+ only. This implies Py3 only.

 2) Drop patch status change notifications, and the associated opt-in/outs.

 3) Drop XMLRPC. pwclient will be rewritten to use the REST API.

 4) Drop the ability to disable tags for a project. Every project will
    use the tags configured for the instance.

 5) Drop Patchwork specific headers, except X-Patchwork-Hint: ignore.
    (i.e. X-Patchwork-State and X-Patchwork-Delegate.) I'm not sure if
    they're used and I think they would be quite surprising to a lot of
    project maintainers and users.

 6) (Possibly) drop support for piecing together unthreaded
    series. (When someone sends patches not in reply to the first
    patch/cover letter.) I think this will make correct series parsing
    easier in the presence of parallelism; if not I'm happy to keep
    it. (I think it might actually be nigh-on impossible to do both
    correct parallel parsing and support unthreaded series, but I
    haven't properly tried yet.)

I would also really, really like to drop MySQL, unless anyone uses it in
production. If you are using it in production, please, please let me
know. Please also let me know if you'd be willing to migrate to Postgres
if I provide a migration script.

I'm still happy to take patches for new features from the community -
please don't interpret this as any sort of feature freeze! (Having said
that, I'd be even happier to take bug fixes, performance fixes, and
general cleanups!)

Regards,
Daniel