Rebases, not merges.

[Ms2ger]

Merge commits are awful for code history. It would be better to rebase PRs and preserve a linear history. This would probably also mean disallowing merge commits in PR branches. The r= note could probably be added to all commits rather than the merge commit.

[Manishearth]

I don't think this should be the default, but having the option sounds good.

[larsbergstrom]

We had some additional conversation about this on Servo at:
servo/servo#1468

[Gankra]

I'm personally pro on a @bors squash flag.

Major contributors already have r+ rights, so they can squash and r=reviewer themselves, so that's not a concern.

Newbies usually have PRs that should be squashed to a single commit and need the most handling, which @bors squash r+ handles perfectly.

This just leaves complex wild-card contributions, which take long enough that the extra roundtrip isn't a big deal IMHO.

[Ms2ger]

A decision about squashing does not necessarily need to block moving to rebases, but note that git rebase has an --autosquash flag that folds commits made with commit --fixup.

[cgwalters]

See servo#19