git - how to get a preview of what Github's pull request diff will look like -

how diff between branches merge diff like

consider graph

*   master |\ | * b1 |\  | * b2 

if im on b2, , person on b1 beat me , merged master,

if do

project>b2 $ git diff origin/master

the diff include b1, not included in pr, how reproduce in command line.

you can update origin/master git fetch origin. update remote branches without changing else.

after that, can rebase b2 work onto origin/master git rebase origin/master. b2 based on latest work including b1. git diff origin/master reflect addition of b1.

then can update pr git push --force.