Google copybara: moving code between repositories(github.com)

170 pointsby reconnecting7 hours ago12 comments

klodolph2 hours ago
Been using this for a while, mostly when I make a tool as part of a larger project and the tool is big enough to deserve its own release.
It’s powerful enough to do a whole bidirectional shipping operation where you export and import code—no thanks, that’s a hassle. I use it mostly for a simple fire and forget export, where I take a folder out of its original repo and preserve the history. Then I just move development to the new repo. The new project layout can be completely different, but Git blame works and I’m happy with that.
- rnagulapalle2 hours ago
  The one-way pattern is actually how Google uses it internally too, syncing outward from their monorepo to GitHub. Bidirectional gets messy because transforms (path remapping, file exclusions, header stripping) are easy to apply in one direction but can't always be cleanly inverted. When both sides have diverged, Copybara's baseline tracking starts producing confusing results because semantically equivalent commits generate different SHAs after transform.
  One thing worth knowing: history "preservation" is actually cherry-picks with rewritten commits, not a true transplant. Git blame works because the file content and authorship carry over, but the SHAs are new. Copybara embeds the original SHA in a commit message trailer (GitOrigin-RevId), which is useful to know if you ever need to correlate commits across repos after the fact.
schrodinger5 hours ago
To those who have used it: is it handy for situations where you have multiple repos that want to share a little code, but it's not worth the trouble of extracting a library, referencing it, publishing versioned releases, updating dependent repos, etc?
And instead just "sync" a code folder from one main repo (perhaps containing common domain models) to other repos?
Basically the Go philosophy that a little bit of copying is better than a lot of dependency?
- ASinclair5 hours ago
  It’s largely used for syncing external open source projects with the monorepo. Policy is to require source code imports over built artifacts. Though you can get exceptions.
  Some projects are also developed in the monorepo and exported via Copybara.
  My team also uses it to version Starlark rule sets internally.
  - paulddraper4 hours ago
    Source code imports versus artifacts really neither here nor there. Go is source code imports too.
    The key part for Copybara is that Google will make changes to the OSS projects from within the internal repo and everyone else will make changes to the OSS projects.
- xyzzy_plugh5 hours ago
  It's for when you have a monorepo internally, and want to publish parts of it as open source to the world. They still need to live in the monorepo, so this is the solution.
  Having a public repo as a dependency for your private corporate repo is a pain in the ass development-wise. Having a tree of such dependencies is a migraine.
  - fiparan hour ago
    It can also be used if you want part of your monorepo to track something open source from the world.
    Say, to rebase upstream MySQL changes onto a fork in the monorepo (in a random, non-specific example)
- klodolph2 hours ago
  Copybara can do that but I think it will be annoying and tedious to use it that way. More annoying than the problem of extracting a library or shoving some files in a separate repo.
MarkSweep5 hours ago
Some other interesting tools in the space. Rust is using a tool called Josh to sync commits:
https://josh-project.dev
The blog post from the Rust people:
https://blog.rust-lang.org/inside-rust/2026/06/04/how-josh-h...
Meta used to have an open source tool called fbshipit. But according to its open source repo they no longer use it:
https://github.com/facebookarchive/fbshipit
Any others in this space?
namanyayg6 hours ago
Nice, I built something similar ~5 years ago using nested git repos and scripts to accomplish a similar purpose of combined private and public repos.
My shell script definitely wasn't google scale tho!
- UnfitFootprint5 hours ago
  Yep, same. I thought it might a wrapper around git subtree but looks like it’s doing quite a lot more!
  For example altering commit author emails during sync
willchenan hour ago
i used this tool when i was at google, extremely helpful in open-sourcing things from google3 to github. still, i'm glad to just directly develop on github now :)
xyzzy_plugh4 hours ago
Copybara is one of those things that you should have set up yesterday.
It works great and I've seen many teams gain significant productivity when collaborating in a monorepo with public bits.
If you're even toying with an internal monorepo you owe it to yourself to give it a try.
jumploops4 hours ago
We’re in the process of open-sourcing a few sub-projects within a monorepo, and didn’t know this existed!
I’m curious what downsides folks have experienced with this tool?
Any tips?
alok-g3 hours ago
Interesting. Anyone knows how this compares to using git submodules and subtrees?
I had used those to create separate repo for website artifacts while the same also remain plugged into the webapp dev repo. (Both sides remain modifiable and changes mergeable to the other side.)
Thx.
neprotivo2 hours ago
If you are using Jujutsu you can achieve a basic way to maintain a public repo from a private monorepo with very little code and without Copybara. I wrote up how to do it here: https://vihren.dev/blog/20260625-jj-public-private-workflow/
- j2kun2 hours ago
  The main function of copybara is not moving code but modifying code to make it suitable for a different repository structure, build system, etc.
syngrog664 hours ago
That seems like a tool easily adoptable by folks engaging in dark patterns on GitHub, particularly the malware bait repos.
lysace6 hours ago
Cute name. (Naming is hard and important.)
- whh6 hours ago
  That tune is in my head again... again...
shizuhalabsai2 hours ago
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