Consider a job is configured with

• Branches to build: Branch specifier: for-master/**
• Additional Behaviours
  • Merge before build
    • Branch to merge to: master
    • Fast-forward mode: --ff-only
  • Calculate changelog against a specific branch
    • Name of branch: master

It is clearly possible, with this configuration, to calculate the changelog and thus identify who should receive failure notifications, even if the branch to build is not a fast-forward.

This isn't done, though, so if someone pushes a branch for-master/foo that is not a fast-forward of master, then the job will fail with a message like this:

ERROR: Branch not suitable for integration as it does not merge cleanly: Command "git merge --ff-only c33c4e240696ae203c257991ef4bfde9a939a4fa" returned status code 128:
stdout: 
stderr: fatal: Not possible to fast-forward, aborting.
...
...
An attempt to send an e-mail to empty list of recipients, ignored.
Finished: FAILURE

The changelog should be computed before the branch merging so a notification can be sent out.