Yeah, I just did some testing, I think we have history.immutable because otherwise arcanist will completly rewrite the first commit with all it's stuff that we don't want :-)

That's a bit why I was saying some kind of per branch git config thing could be used too.

Mmmm, we have history.immutable: true in our .arcconfig, so that's why arc diff is not doing it, I'll investigate a bit more, thanks :-)

Mmmm, do you mean if I put "Differential Revision: DXXX" as the last line of the first commit of the branch, it'll be seen by arc and any subsequent arc diff will update the right review instead of creating a new one ?

In T8763#124830, @epriestley wrote:

Use arc which to understand what arc diff will do and why.

arc already uses commit hashes (works better for immutable workflows) and "Differential Revision: ..." in messages (works better in mutable workflows) to track revisions. We do not use branch names because some users put multiple changes in the same branch.