Oh my god you’re right. Edit: none of this comment is sarcasm! genuinely dumbfounded

git checkout branch1
git treesame-commit branch2 # a complex program

is the same as

git checkout branch1
branch1ref=$(git log --format=%H -1)
git reset --hard branch2
git reset $branch1ref
git add .
git commit -m "treesame-commit" # no complex program

and this whole time I believed there was no way to do this!

In my literally 7 years of using my own custom tool that writes git commit objects by hand, how have I never realized that? :headdesk:

Of course, to make the latter really solid you’d also want a git clean -dffx, git submodule sync, git submodule update --init --recursive, etc. In some sense, it’s hard to beat the concreteness of writing out the exact tree hash you want into a commit object, so frankly I’ll probably still keep using my tool but I do feel a bit sheepish.

Another person on reddit pointed out git read-tree and git checkout-index which also can solve the problem.

Let’s say you have some complicated history pattern with merges and so on. Lots of different developers doing lots of different things. After a bunch of merges and merge conflict resolutions you have a history of sorts, but you want to clean it up. This allows you to make a single commit where the end result is the tree matches the complex history you’d like to throw away.

Very useful for keeping dev history clean.