I have a branch, mybranch, that has six commits and stems from commit C. I would like to create a new branch, also based on commit C, that effectively includes all the commits from mybranch, squashed into one commit. What's the easiest way to do this?
I need to do this due to the mantra of "squash before you git-push". For the new branch, I don't want any mention of mybranch in the history pushed up to the remote server. The reason I want to create a whole new branch used to push is because I'd like to keep all the commits in mybranch for reference.
Why only push squashed commits? That sounds crazy (and wrong).
But to answer your question:
git checkout -b newbranch # checkout new branch
git reset --soft C # move to commit C
git commit -m 'squashed commit'
Another possibility would be to use rebase -i to squash/fixup all commits into a single one:
git checkout -b newbranch
git rebase -i C # now, replace every 'pick' with 'fixup'/'squash' except the first one
Also of interest is git merge --squash:
Produce the working tree and index state as if a real merge happened (except for the merge information), but do not actually make a commit or move the HEAD, nor record $GIT_DIR/MERGE_HEAD to cause the next git commit command to create a merge commit. This allows you to create a single commit on top of the current branch whose effect is the same as merging another branch (or more in case of an octopus).
git checkout -b newbranch C # create newbranch at commit C
git merge --squash mybranch
git commit -m 'squashed commit'