The forward port process adds a uniquifier to the branch name as it's
possible to reuse branch names for different sets of PRs (and some
individuals do that systematically) which can cause collisions in the
fw branches.
Originally this uniquifier was random by necessity, however now that
batches are reified and forward port is performed batch-wise we don't
need the randomness we can just use the source batch's id as it's
unique per sequence of forward ports. This means it'll eventually be
possible for an external system to retrieve the source(s) of a forward
port by reading the batch object, and it's also possible to correlate
forward ports through the batch id (although not possible to find the
source set without access to the mergebot's information).
Do the same thing for backports, because why not.
- fix incorrect view specs (the action id comes first)
- add a wizard form and hook it into the PR, completely forgot to do
that
- usability improvements: filter branches to be in the same project as
the PR being backported, and older than the current PR's branch
The latter is a somewhat incomplete condition: ideally we'd want to
only allow selecting branches preceding the target of the *source* of
the PR being backported, that way we don't risk errors when
backporting forward-ports (the condition should be checked in the
final action but still).
Also we're only filtering by sequence, so we're missing the name part
of the ordering, hence if multiple branches have the same sequence we
may not allow selecting some of the preceding branches.
This is not a full user-driven backport thingie for now, just one
admins can use to facilitate thing and debug issues with the
system. May eventually graduate to a frontend feature.
Fixes#925
