Trunk Based Development
trunkbaseddevelopment.com72 points by handfuloflight 3 days ago
72 points by handfuloflight 3 days ago
I've rarely seen the first description of it where people actually commit directly to main. Except in very early stage projects. But it does always feel the fastest if you only review code "on-demand" in PRs/MRs instead of enforcing it for every change.
I think in a team with good ownership, enforcing formal reviews slows down a lot. But of course in a larger code base where no single engineer can understand all the effects a change might have, having a bit of knowledge sharing and 4 eyes enforced is often the better approach than yolo-ing it.
Then again I did build an SQL review tool for database access because I felt like "yolo-ing" production access was also not the way it should be. It's an interesting slider between full autonomy and strict review processes where each team needs to find their sweet spot: https://github.com/kviklet/kviklet/
As I understand it, trunk based development does not call for committing directly to main. It says to avoid long-lived branches for releases, whole features, etc.
There's nothing wrong with small, short-lived branches that can be quickly reviewed and merged into main.
That being said, I've been in a small team where the blessed style was to commit directly to main and do reviews "on demand". It quickly gets features deployed in a way that builds a lot of rot and debt into your project that people quickly lose a good understanding of. Then you just keep piling.
There's probably a way to get this done properly with a tiny team of very experienced and well-aligned developers; but that's usually not what you have in an environment that pushes this kind of extreme no-review-interpretation of trunk-based development.
Slow down, do reviews, avoid keeping branches open for more than a day.
What counts as "long-lived"? Our shortest lived branches are quick fixes because something got merged into main that doesn't work properly.
I'd like main to always be ready for production, but that seems an elusive goal no matter what git workflow you use.
The best way to prevent complex merges does not depend on your git strategy, but on how modular you make your code. If a change requires changes to only a single file, and your files aren't too big, there's little chance of conflict. The more files need to be changed (often because the same thing needs to be declared in 4 different places), the bigger the chance of conflict. Same with larger files. Each file should have a single concern.
For the purposes of this discussion, I'd say a "long-lived" branch is one that keeps running into merge conflicts with other code that's been developed in ignorance of the branch's contents, or a branch that acquires enough changes to not be easily reviewable in its entirety. But generally, I'd say if it lives longer than a day, that's getting too old. (Exceptions apply.)
Code should live in main/master and be in a production environment as soon as possible, but it does not have to run for all, most or even any customers/clients from the start. You can gate it behind feature switches, preprocessor directives, global constants, whatever. As long as it has an active purpose and is being developed further, it is not dead. Ideally, it will have tests.
The result of merging back to main often is that other changes will be made in awareness of your new code, and all merging will happen organically and in small increments. You also get to develop complex features bit by bit, in a way that can be verified in a real environment in a controlled way. And everything can be deployed anytime, which should happen often.
Being able to verify incrementally and get quick feedback lowers the risk of otherwise releasing a hitherto completely untested large feature into the wild in one go.
This does not absolve you from making sure that your changes actually work as intended. That will be easier if you portion the work into smaller chunks that are easier to understand than a whole, complex, all-or-nothing feature.
Of course you will still have to make sure that your small chunks fit together and make up a good "whole". However, the idea is that you're doing this exact work anyway when developing a larger feature on the side, but you might as well cut it up to deliver in much smaller increments.
This approach has its own costs and drawbacks, but in my experience it often produces a substantial net-reduction in friction and accumulated complexity and risk, and it keeps things moving, which is a benefit on its own. This is from my perspective in backend development, and it will not apply universally, but widely. Essentially, whenever you can get away with it, you should strive to deliver like this.
> well-aligned developers
I think this is very key, if the development style and the direction of the project is clear, much less review and alignment is necessary.
And also
> avoid keeping branches open for more than a day
Big +1 on that, fast reviews are extremely key. Most teams I have seen often took days or even weeks to merge branches though, often because you end up waiting too long for reviews in the first place. Or because of good old bike-shedding. But also because these code reviews often uncovered uncertainties that needed longer discussions.
However usually code is easy to change, so defaulting to "just merge it" and creating followup tasks is often the cheaper approach than infinite review cycles.
I think it's still worth-while to do reviews. A second pair of eyes does wonders, and it spreads knowledge of what things exist and how they work. If changes are small, reviews can be quick. It's possible to keep building on top of code being reviewed, and even easy when using modern VCS tooling like jujutsu.
Once the code is merged, chances are it will not get changed Those follow-up tasks will be displaced by more pressing work that will keep piling onto a slightly unstable foundation, increasing the tilt over time.
There is an excluded middle between "no reviews" and "infinite review cycles": proper, timely and efficient reviews. They are worth investing the time to get right. They will start paying dividends months down the line, and boy will they keep paying.
This is not about trying to get things perfect from the get go, but to get them done right while you're there. "We'll fix it later" is not gonna happen, and is much more expensive than it initially seems.
> However usually code is easy to change, so defaulting to "just merge it" and creating followup tasks is often the cheaper approach than infinite review cycles.
I wish this was the "default" mindset everywhere, especially in those cases where you have that one colleague that loves to nitpick everything and doesn't see an issue with holding up both releases and wasting your time over menial pedantic stuff. It would be so much easier to merge working code and let it work, and keep those TODOs in the backlog (e.g. trash).
In a sane world, code review would be like:
1. Will this work and not break anything? We checked it, it's okay. There are no apparent critical or serious issues here.
2. Here's a list of stuff that you can change if you wish, here's why it might be an improvement.
3. Okay, we have some left-over nice to haves, let's keep track of those for later (or not) and merge.
> "Scaled Trunk-Based Development"
> There's nothing wrong with small, short-lived branches that can be quickly reviewed and merged into main.
I would have called this "branch based development", personally.
Hmm, branches you say? Branches that contain features?
https://www.atlassian.com/git/tutorials/comparing-workflows/...
But yeah, that’s what people generally settled on, naming wise.
In my previous job we worked like this. We had one dev branch that everyone pushed directly to and the dev branch was eventually branched to an RC branch which in turn was merged to master once the release was complete.
The team was small, around 6 people, and the codebase was maybe medium sized (~500k LOC). There was no formal review process, instead it was up to each team member to ensure the quality of their own and others code. In practice I would read through all commits that came in the previous day while having my morning coffee. If there was some egregious I would talk to whoever made to commit to make discuss if something should change, but this was fairly rare.
Formal PR reviews were only ever really used for new members or for bigger/sketchy changes where someone wanted more eyes on it.
Because I ended up reading most commits, I ended up knowing how pretty much the entire codebase worked. It takes a while for this to develop, but the more you do it the better you get at it, especially in the context of a single codebase.
I work in games, and we do commit directly to main. On a smaller team you can get away with pre submit review, post submit checks. On a bigger team you need pre submit checks but honestly the point where you need this is much much later than you think. One of my previous projects had 100+ people committing directly to main with no pre submit checks and jt broke once or twice a day. The builds took longer than that to go through so you just always sync to “last known good”
We're organized in small teams around specific products. That leads to mob programming being a good fit, so code reviews and knowledge sharing is organic. This gives us an opportunity to commit to main and do direct deploys to production. Treating every commit as deployable is key, but it drives good practices.
Working without branches, except for releases, is the most effective way of working, using rebase instead of merge to get a single line of commits. Even release branches can be avoided with continuous deployment.
> Working without branches, except for releases, is the most effective way of working, using rebase instead of merge to get a single line of commits.
I think you're confusing workflows with commit history.
You can work with feature branches all you want, rebase them as you feel like it, and then do squash merges to main.
The likes of GitHub even have a button for this.
Why in the world would you do squash merges? ...except to clean up messy mini-branches written by total noobs. I don't do separate commits for funzies. If you want separate commits for ease of review, why not for later reading of the code.
Assumption: above mentioned total noobs don't use git rebase -i or equivalent, everyone else does
It’s pretty hard to keep the commits in a working branch in a good legible state - certainly it takes work to do it.
In 25 years of professional development I’ve never really had a situation where the commits on a branch would have helped me understand what was going on a year ago when the work was done. That includes pretty big bits of project work.
I’d much rather have a trunk with commits at the granularity of features.
I on the other hand have never come across a scenario where I run git bisect to find a commit that broke something, discover a small commit as a culprit and wish I had instead found a commit that's hundreds of lines long.
What has happened a whole lot though is the exact opposite.
It might be better to view a commit as a natural unit of working code. There are a lot of units of working code which would be tedious to be introduced as a only a few lines.
As such, a new codebase is likely to grow by large unwieldy commits and a mature one by targetted small commits.
For me, all the code in the PR at that point is in question. The code was changed as part of a bigger part of work and reverting it without understanding why might cause issues back the other way.
The other thing to say - that is missing from this conversation - is that if you’re using github, the original commits are still against the PR.
Our strategy is to squash on merge and ensure the JIRA ticket reference is in the MR title. You have the granularity of the feature which is going to help guide you on the intention. It's also much easier to enforce. People like to write and commit code in their own way.
`git log --merges --first-parent` gives you both.
I've had separate commits come in handy several times when `git blame`ing when working with people who actually described what changes were about in their commits (which, unlike comments, don't go out of date).
In 25 years of professional development I have several counter examples where some bit was either a trivial git revert of a single commit - among multiple ones in a branch - away, or an absolute pain because the squash-merge commit had flattened too many concerns together, concerns that were perfectly split in the topic branch but that branch was long gone by virtue of being auto-deleted on PR merge.
Coincidentally, every single squash-merge commit advocate I've had the unfortunate debate with was a regular practitioner of public tmp / tmp / try again / linter / tmp / fix / fix / haaaaaands commits.
Note that I'm not against squashing/history rewriting e.g rebase -i and stuff (which I'm a heavy user of so as to present sensible code aggregation reviewable per-commits), only squash-merge.
I take it you haven't had the pleasure of working with your average ("dark matter" as they're called here) developers. I wouldn't call myself an "advocate" of squashes, but it's often the only practical way of keeping git history somewhat usable when working with people who refuse to learn their VCS properly.
I chunk my changes into tiny commits ("linter"/"tmp"/"wip"), but then rebase aggressively, turning it into a set of logical changes with well-formed commit messages. git bisect/revert work great with history written in this way even years layer.
But: most of the people I've been interacting with also produce lots of "wip"/"tmp", but then skip the rebase. I can only offer my help with learning git rebase for so long before it starts taking too much time from the actual work. So squash it is: at least it produces coherent history without adding thousands of commits into `--ignore-revs-file`.
And sometimes, a patch is just that big. especially in UI works where a single change can cascade down to multiple layers.
> I chunk my changes into tiny commits ("linter"/"tmp"/"wip"), but then rebase aggressively, turning it into a set of logical changes with well-formed commit messages. git bisect/revert work great with history written in this way even years layer.
In a PR based workflow, it has become easier to have the PR be a logical unit than to `rebase -i` all the time on my end.
If you work with a ticket system, squash-merge gives you the same granularity, where a commit would refer to a single ticket.
A ticket should be atomic describing a single change request. PR in this case are the working room. It can be as messy or as clean as you want. But the goal is to produce a patch that introduces one change. Because if you would rebase -i at the end, you would have a single commit too in the PR.
No, you wouldn't. git rebase -i is to remove noise, which is about merging commits that, well, make more sense together than apart. Which is mostly about summarizing trivialities (e.g. several typo fixes) and squashing fixups into commits that introduced a problem in the same branch.
A typical bugfix branch might look like this after rebase -i:
Move property to a more appropriate place
Improve documentation of feature Foo
Fix accidental O(n^2) in feature Bar
Fix interaction of Foo with Bar
Those looks more like noise to me. A squashed merge (or a final squash before PR) would be:
TN 43 - Fix mismatched interface between Foo and Bar
We've moved the X property to a more appropriate place and
improved the documentation for Feature Foo. We've also found and fix
an O(n^2) implementation in feature Bar.
The commit message is what's more important. I don't think I've ever needed what is in a merged branch. But I've always wanted the commit at one point to have tests passing and a good description of the patch. And all the talk in the engineering team are always about ticket. It does makes sense to align those.
They aren't noise at all and have found them useful a bunch in the past when I worked at a place that didn't squash. Commits at this level act as immutable comments that don't get out of date. Provided you do --no-fast-forward merges, the merge commit is the feature commit and you can get the "clean" feature history with `git log --merges --first-parent`. Best of both worlds! Being able to `git blame` and get a granular message about why something was done can be really handy, especially when looking unfamiliar code.