As far as I know, this is not possible in the current release of Review Board.
The repository may have been committed since the review was posted, and this means that diff might fail. Since reviews usually take some time, I believe that this feature would not be feasible in general use, except for edge cases of a rarely updated source.
Review Board 2.0 should support extensions , and IMHO looks like work for extensions, not for the main function.
Helgi source share