Undo a fast-forward merge

Solution 1:

If you reset the branch master, it won't touch develop branch. In order to reput all in order, you should do:

git checkout master
git reset --hard sha-of-B
git checkout develop
git reset --hard sha-of-D
git checkout master
git merge develop --no-ff

Solution 2:

• imagine you are still on master where you merged and pushed
• git reset --hard @{1}
  • this resets branch “master” to where it was one step back on your computer (i.e. at “B”)
• for develop do nothing, because it should still be at “D”
• git push publish develop
  • this pushes branch “develop” in the usual way
• git push publish master --force-with-lease
  • pushes branch “master” backwards, with the permission gained via --force-with-lease in a safe way
  • the use of --force might silently overwrite work from others, so I never use that
• or both push operations together with this surprising syntax:
  • git push publish develop --force-with-lease=master