Pushing Changes Back Upstream with Subtree Split
Learn how to extract changes made inside a subtree and push them back to the original upstream repository using git subtree split and push.
Pushing Changes Back Upstream with Subtree Split is a free Git Advanced: Monorepo, Submodules & Workflows lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Git Advanced: Monorepo, Submodules & Workflows learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Two-Way Subtree Workflows
Subtree is not just for pulling code in. One of its strengths is the ability to contribute changes back to the original project. This makes subtree a genuine two-way integration tool.
The key command is git subtree push, powered internally by git subtree split.
What 'split' Does
git subtree split walks your history and produces a synthetic branch containing only the commits that touched the subtree's prefix, rewritten as if that folder were the repo root.
This is what makes the changes mergeable back upstream.
Recap: Adding a Subtree
Assume you added an upstream library under vendor/widget earlier. Now you have made improvements there and want to share them.
git subtree add --prefix=vendor/widget \
https://example.com/widget.git main --squashCreating the Split Branch
Run split to create a branch with just the subtree's history rebased to the prefix root.
git subtree split --prefix=vendor/widget -b widget-upstreamInspecting the Split
Check out the split branch and confirm its files live at the root, not under vendor/widget. This proves the rewrite worked.
git log --oneline widget-upstream
git ls-tree --name-only widget-upstreamPushing the One-Step Way
You can split and push in a single command. git subtree push does the split internally and pushes the result to the upstream remote and branch.
git subtree push --prefix=vendor/widget \
https://example.com/widget.git contrib-branchOpening a Pull Request
Push to a feature branch on a fork you control, then open a pull request upstream. Your subtree commits appear as ordinary commits on that project, ready for review.
Keeping Splits Fast
On large histories, split can be slow because it re-walks commits. Subtree caches rewrites; passing --rejoin writes a merge commit so future splits start from there.
git subtree split --prefix=vendor/widget --rejoinAvoiding Mixed Commits
Split works cleanly only when commits are scoped. A commit touching both the subtree and unrelated app code becomes awkward upstream. Keep subtree changes in their own focused commits.
When to Push Back
Push upstream when your fixes are general-purpose and the maintainers accept contributions. For private, repo-specific tweaks, keep them local and never push them back.
Pulling Their Acceptance Back
After upstream merges your contribution, pull it back into the subtree so your superproject and the original project converge again, closing the round trip.
git subtree pull --prefix=vendor/widget \
https://example.com/widget.git main --squashQuick Check
Test your understanding of subtree split and push.
Recap
You learned the two-way subtree workflow: split isolates subtree commits into a prefix-rooted branch, push sends them upstream in one step, --rejoin speeds up repeated splits, and keeping commits focused makes upstream contribution clean.
Frequently asked questions
Is the “Pushing Changes Back Upstream with Subtree Split” lesson free?
Yes — the full text of “Pushing Changes Back Upstream with Subtree Split” is free to read here on the web, and the Git Advanced: Monorepo, Submodules & Workflows course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Git Advanced: Monorepo, Submodules & Workflows course, upgrade to CoddyKit PRO.
What will I learn in “Pushing Changes Back Upstream with Subtree Split”?
Learn how to extract changes made inside a subtree and push them back to the original upstream repository using git subtree split and push. You practise Git Advanced: Monorepo, Submodules & Workflows with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Git Advanced: Monorepo, Submodules & Workflows?
No prior experience is required. Git Advanced: Monorepo, Submodules & Workflows on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Pushing Changes Back Upstream with Subtree Split” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Git Advanced: Monorepo, Submodules & Workflows lesson?
Yes. Every Git Advanced: Monorepo, Submodules & Workflows lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Introduction to Git Subtree
- Adding and Merging with Subtree
- Subtree vs. Submodule Comparison
- Pushing Changes Back Upstream with Subtree Split