Characteristics of a Good Merge Request

If you happen to use Merge Requests as a basic mechanics of your software development workflow (and there are compelling arguments that you should), you’ve probably encountered some merge requests that could be handled in a straight-forward manner and some that are just painful to work with. Some merge requests “spark joy” and others elicit nothing but displeasure.

What differentiates the good, joyful merge requests from the dreadful? We’ve found six (or seven, based on your categorization) characteristics that good merge requests exhibit, while bad ones don’t.

Good merge requests are:

  • Atomic – Only one topic
  • Minimal – Only necessary changes
  • Curated – Double-checked by the developer
  • Finished – Free of deactivated code, debug code, etc.
  • Explained – Provided with commentary in the merge request (not the code)
  • Manageable – Small in changeset size
  • Separated – Either domain-based or technology-based, not intermingled

Bad merge requests lack in some or even all these categories. The first three aspects are ignored the most in my experience. This is why they are at the top of the list. A lot of trouble vanishes simply by staying on course, being succinct and caring about the next pair of eyes as a developer.

Let’s look at each characteristic in some depth:

Atomic

Let’s say you watch a romantic comedy movie and halfway through, all of a sudden, it changes into a war movie with gruesome scenes. You would feel betrayed. Ok, we don’t work in entertainment, our work is serious. Let’s say you read a newspaper article about the latest stock market movement and in the third paragraph, it plainly changes into a car advertisement. This is called “bait and switch” and is a diversionary tactics or a feint. If you do it unwittingly, you might mean no harm, but still cause irritation.

An atomic merge request tells only one story which means it contains changes for only one issue. If you happen to make “just a quick fix” at the wayside of your task, you break the atomicity property of your changeset and force your reviewer to follow your train of thought, but without the context.

There is nothing to say against a quick fix or a small refactoring, a little improvement here and there. But it’s not part of your story, so make it a story of its own. Bundling the tiny change with the overarching story makes it harder for the reviewer to differentiate topical changes from opportunitic ones and difficult to accept your main changes while rejecting your secondary ones. If you open up a second merge request for your peripheral changes, you retain the atomicity and the goodwill of your reviewer.

Minimal

A good merge request contains only changes that are essential to the story and consciously modified by the developer. Because we use a plethora of development tools that all want to store their metadata somewhere in our project, we often end up with involuntary modifications in files we don’t know, never looked at and don’t feel responsible for.

The minimalistic aspect of a good merge request puts you, the developer, into the position of responsibility of all content in your changeset. It doesn’t matter that “a tool made that change”. The tool acted on your command. It is not the responsibility of the reviewer to figure out what that change means. It is your duty. Explain the change to your reviewer and if you can’t, revert the change. If the rest of your changes work without it, it wasn’t necessary and shouldn’t have been included anyway. If your changes don’t work anymore, you are about to learn the inner workings of your development tools.

A minimal changeset also implies a reduced number of modified files. That’s true, but you shouldn’t design your system to have an artificial low number of files (or parts). If you don’t space out your code according to domain structures, you’ll end up with small changesets, but lots of merge conflicts and an ongoing dissonance between the domain model and your software model.

Curated

If you can follow the concept of a merge request telling a story, then you are the storyteller. You need to take care of your narration. In a good story, only necessary bits are told. If you muddy the water by introducing meaningless details and “red herrings”, you essentially irritate your listeners for no good reason.

At least have a second look at the changeset of your merge request. Is there any change present by mishap? That happens often and is not a sign of bad development. It is a sign of neglected care for your teammates if you let it show up in the changeset review, though.

Bring yourself in a position where you are fully aware of your story and the bits that tell it.

Finished

Your merge request should tell a complete story, not a fragment of it. It also shouldn’t show the auxiliary constructs you employ while developing your changes. These constructs might be debug output statements, commented out code, comments in the code that serve as a reminder for yourself (TODO comments play a big role in this regard) or extra code that ultimately proved to be unnecessary.

Your merge request should not contain any of that. After the merge, the resulting code base is regarded as “finished”. Any temporary content will stay forever.

Explained

Your story is probably very clear and recognizable. If not or if parts of it are more obscure than you hoped it would be, it is good practice to provide an explanation. It is your decision to explain yourself in the code (in form of an inline comment) or in the merge request itself (in form of a merge request comment). My preference tends to be the latter, because the comment will not be part of the “eternal” code base. The comment is a tool to help the reviewer grasp the details. Your approach may vary, but there needs to be some form of extra explanation from your side if your code isn’t crystal clear.

Manageable

The best stories are short. Humans aren’t good at keeping large numbers of details in their head and your reviewer is no exception. Keep your merge request small to make the review bearable. A good rule of thumb is a merge request containing no more than 10 files or 250 lines of changed code. While these numbers are arbitrary, they serve the purpose to give you a threshold you can check. You can’t check the real threshold of your reviewer, so try to stay below it.

If you find yourself in a position where a lot more files are touched and/or the changed lines of code are way above 250, you should think about what lead you there. These changes didn’t happen on their own. Your work produced them. Can you adjust your workflow so that smaller milestones are possible? What was the developer action that produced most of these changes? Are we looking at a shotgun surgery?

It is easier to review several small merge requests than one big one. Big, unmanageable merge requests may happen, but they should be the (painful) exception. Learn to work in episodes.

Separated

One aspect of software development is that we tend to mix two types of development into one stream of actions: There is development that produces new domain functionality and is inherently domain-based. And then, there is development that is required by technology but probably can’t be explained to the domain expert because it has nothing to do with the domain. Both types of code work together to provide the domain functionality.

But if you look at it from a story-telling aspect, then domain code is a novel while the technical code is more like a manual. Your domain code is probably unique while your technical code very much looks the same as in the next project. You should try to separate both types of code in your code base. And you should definitely separate them in your merge requests.

Keeping your domain related changes separate from your technical changes gives your reviewer a chance to ask the right questions. With domain code, some aspects are that way because the expert says so. There is no “universally correct way” to do these things. It might look strange or even wrong, but that’s the rule of the domain.

Technical changes, on the other hand, tend to look the same, no matter the domain. You can apply technical experience to these kind of changes regardless of context. Refactorings are the typical member of these changes. Renaming a variable or method will inevitably lead to a lot of changes in a lot of files. But it won’t affect the domain functionality (that’s the definition of a refactoring!). Keep your refactorings out of domain changesets to keep your reviewers happy.

What next?

There is a lot of adaption to be done from a “normal” development practice to one that tends to produce merge requests with these characteristics. These changes in behaviour don’t happen over night.

My proposal would be to start with one aspect and focus on it for one month. Starting with “Atomic” will have the most effect, but you can choose your starting point according to your preference. Just keep it for one month. After that, you can choose to focus on another aspect for a month or add another aspect to your focus group and now keep two aspects in mind. The main goal of this approach is to form a habit that enables you to produce better merge requests without really thinking about it. It might take some time, lets say a year or even two to incorporate all aspects in your day-to-day working style.

After that, you’ll probably look back on your earlier merge requests and smile because you see proof that you can do better now.

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