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We're rolling out a series of bug fixes for the issues with squash merging.

There's an internal system we have called CPRMC (Create Pull Request Merge Commit) that is used to evaluate whether a PR is "ready" to merge. This covers everything from mergeability (checking for merge conflicts) to rule evaluations (ensuring that approvals match the potential commit that will be created by merge) and more.

This becomes particularly difficult when squash merging a stack of multiple PRs because we have to calculate a series of squashed commits, then associate those back to the rules/reviews. This is relatively easy for the first PR, but for the second PR onwards this gets more complicated because the ancestor commits are squashed and don't exist on the branch as-is. And I won't get into how much more complicated it gets for multi-parent situations lol.

It's something we need to fix and it's the top priority for the team. Our numbers show that 99% of stack merges go through successfully, but we need to get that much higher.

Thank you for being an early user in the preview and bearing with us while we work out these issues!

> There's an internal system we have called CPRMC (Create Pull Request Merge Commit) that is used to evaluate whether a PR is "ready" to merge. This covers everything from mergeability (checking for merge conflicts) to rule evaluations (ensuring that approvals match the potential commit that will be created by merge) and more.

By the way could there be a way to disable that when doing integrations externally? It seems to be quite costly (which makes sense), and the pull/ refs kinda bloat the reflist.

I’m sure that external integration is not exactly beloved internally but there’s really just a small handful of big annoyances which would make it so much nicer and more comfortable.

Can you make sure there is good API support for stacks?

We use a custom merge queue and we want it to be able to land multiple PRs from a stack at once as separate PRs. Last I checked you had to land a single PR, rebase the stack, land the next and so on. This is very expensive in CI time (and wall clock time), vs simply testing part or all of a stack in parallel then declaring those merged. In essence a robot needs the ability to say “squash merge these 3 stacked PRs”, after the queue does its thing.

Yes that was one of our top priorities. For one, there's a fully public API for all stack operations. So if you don't want to use the `gh stack` CLI, you can build your own: https://docs.github.com/en/rest/pulls/stacks

For merging, we have an API but had to move it to a new async method: https://github.github.io/gh-stack/reference/merge-api/

The legacy API was fully synchronous, and since stacks of multiple PRs can often take more than 10s (our global timeout), we had to move to async.

We've had some folks already use this to integrate stacks into their merge queues. The great part is you can land multiple PRs in one atomic operation, and then there's one push to main with all your commits from multiple PRs. So instead of having to rerun the build/deploy for each, it can trigger for the last commit that contains all of the changes.

Is there also a webhook? I don’t fancy busy-looping on dozens or hundreds of PRs for tools with large scopes of overview.

Also what about external merges? Is there a way to sanely interact with stacks when merging locally or via external tooling?

Hey there - we worked with Sameen and the team at GitHub over the past month to get support for stacks in our Mergequeue: https://trunk.io/blog/trunk-merge-queue-now-supports-github-...

They do indeed have APIs you can use in your mergequeue, I'm happy to share notes on how we built it so you can add it to your mergequeue.

Does trunk use GitHub’s api to merge stacks, or does it do the integration internally / on its own?

We use GitHub's APIs. We did build a version before GitHub supported it, but it required using our credentials to push directly to the main branch. That wasn't acceptable to most of our customers, so we ended up not shipping it and waiting for GitHub support.

Using the GitHub APIs means you still preserve history and commit messages they way people expect (merges through the queue and direct merges behave the same), and it lets users guarantee that the only code our mergequeue merges is the code that was in the PR.

lovely website animation :D

Thanks! :)

> This becomes particularly difficult when squash merging a stack of multiple PRs

I acknowledge that it is not trivial.

But this is 2026. Many people have solved this in in-house solutions. Every place I have worked at in the last 10 years had solutions in place. Some had wrinkles but it all worked in the end. Github sees itself as the leading provider of solutions in that space and has MSFT backing. Just saying that it's difficult is not good enough, quite frankly. People have been complaining about GH support for this for a long time.

> But this is 2026. Many people have solved this in in-house solutions. Every place I have worked at in the last 10 years had solutions in place. Some had wrinkles but it all worked in the end. Github sees itself as the leading provider of solutions in that space and has MSFT backing. Just saying that it's difficult is not good enough, quite frankly. People have been complaining about GH support for this for a long time.

But most of those solutions don't have the number of integrations and rules executions that GH has and that's where the challenge lies.

Again, it's by no means trivial. But in the last years we as an industry made private space travel viable, created self driving cars and made chatbots that can explain humor. Not being able to do stacked PRs in this day and age by the prime company in this area is just .. well you got the point.

The feature is half baked. Just today I had to spend ~1hr untangling a mess it created. And there was no way to reorder the Stack without discarding PRs that already had many comments. I'm not an intentional an early adopter, someone on the team clicked the tooltip.

> For example, merging an entire stack is completely broken in many cases: https://github.com/github/gh-stack/discussions/212

> You can merge one by one, but if you're using squash and merge, you need a re-approval for each PR in the stack if you require reviews. This makes you lose out on arguably the biggest gain of stacked PRs.

I'm struggling to imagine what it offers at all if that doesn't work! Is it just a way of manually marking another MR as a dependency in the UI so that it shows up with a red X if the other one isn't merged yet?

Not everybody uses squash and merge. Regular merge, I imagine, would work fine.

Sure, I just think that "merging one by one" defeats the purpose of stacked PRs even if you don't need re-approval. You can already avoid re-approval today without needing re-approval if you're not rebasing (which is not what I'd expect you mean by "regular merging"; it sounds like you mean just having a merge commit) by just not clicking merge until the other PR merges first, and at that point. That's what I meant by it sounding like all this offers is an icon telling you whether that other one already merged or not.

Stacked PRs are so hard to implement for software not natively designed for them. Gitlab has been struggling with them too, despite 2.5 years since the MVP (https://gitlab.com/gitlab-org/cli/-/work_items/7473) . It doesn't help they want to do it without making any significant change outside the CLI, or that most developpers just... don't get it.

We just today ran into a bug where if the branch a stacked PR points to is deleted, it can just stay stuck in "merging" without any additional feedback. I directly looked at the GH status page, because who knows, maybe the PR subsystem has a partial outage again, but no, it was just a bug in the stacked PR feature.

Thanks, definitely sounds like a bug. Will look into this.

It's been >4 years since I've been out of Facebook and now have to use Github, and to this day I miss phabricator and landing stacked changes. When I first left and had to work with github I hadn't realized that this, to me, very basic, workflow is _not_ a feature!

the whole industry has become completely “ready, fire, aim” since 2021

GitHub has been especially bad.

Ultimately they have become a monopoly so it is kind of expected.

So many things on Github are now broken or utterly unusable, that this comment is not wrong. I mean even the code viewer/display is utterly broken and doesn't even perform standard text highlighting correctly. The folding marks often make no sense or are inconsistent. If one wants to see all forks of a repo, one has to go through "insights", I think few would suspect it to be located, and it doesn't show _all_ forks, according to the number displayed next to the fork button. The list of UI issues goes on and on. But then there are also the reliability issues, things being down every 2 weeks, or is it every week by now? Difficult to keep up with it really.

They are a monopoly in certain regions of the world.

Even though I live in a western country, just one of my clients after all these years of being self-employed, uses GitHub.

Nobody else would ever use it. And why would they? Especially for proprietary applications.

That's interesting, I get pushback when I suggest anything different and for devs under 30 I've had to remind them that git and github aren't the same thing. This is not to cast aspersions on them, just the state of things in the places I've worked.

Microsoft seems to be running the classic embrace, extend, extinguish playbook on github/git though. When it becomes impractical to join a team's workflow without github specific tooling then everyone will be forced to use gh.

You’re surprised? Really? I’m more surprised that they pushed a major change and the site is still up.

what if you stack a draft PR on top of a regular one?

The draft one can't be merged, but the one below it isn't affected and can be merged as long as it's green. The dependency goes bottom-up.

hahahah yeah my company had sooooo many issues with this stuff and merge queue lately

If you thought git was complex, wait until you get your 5 deep stacked PR from that nice coworker! Jokes aside this is really an anti-feature. Now coworkers can blow off your PR for much longer.