I am currently on commit 123456 and branch foo. I'd like to add a new commit to branch bar with the exact contents of 123456 (not rebased, just created from the same snapshot, so the diff will be whatever it will be).
I can accomplish this like so:
$ git checkout bar
$ git reset foo
$ git commit -am '...'
$ git checkout foo
I have two questions:
foo or needing to change my working tree?It's easy to do
git checkout bar
git restore --worktree --staged --source=foo -- .
git commit -m "Here we make it just like 1234546 (or foo back when I created this commit)"
You can use git commit -C 123456 to use that commit's information for the new commit but it would be misleading because you are creating a single commit and you are disregarding all history in foo..bar.... does it make sense to do that in a single commit? Well, perhaps it does for your use case but I wouldn't assume it will work for everybody.
And sure, it can be done without changing your working tree.... by using a superduper second working tree. So, check git help worktree.
Now that I think about it, there is yet another way to do it without having to move a single bit from your working tree and without needing a second working tree, but it's hackish:
# we are on foo, right?
git branch temp $( git commit-tree -p bar -m "Here we make it just like 1234546 (or foo back when I created this commit)" 123456^{tree}" )
# commit-tree is a command not intended for the faint-of-heart. It
# will create a new commit just like 123456 in contents and that has bar
# as its parent.... and the outer command will set the branch temp
# on it.
# It's a hackish thing so no -C available to copy the info from
# 123456.
# if you like it, then move bar to that position
git branch -f bar temp
# and now you can delete temp
git branch -D temp