Using a code formatter plugged onto maven

[slandelle]

Netty currently relies on checkstyle rules.
This is pretty cumbersome for contributors:

• either you have to figure out where these rules are defined and import them in your IDE, while they might conflict with the ones at your real job
• or you try to apply them blindly and rely on trials-and-errors with Netty's CI to fix the formatting

Nowadays, the most standard practice is to plug code formatting on the build tool. This alleviate the need to configure anything custom in the IDE.
In Java+maven the most standard solution is spotless. Every Java project is basically moving away from checkstyle and adopting spotless instead.

It's been a bliss using it at Gatling, eg https://github.com/gatling/gatling-maven-plugin/blob/main/pom.xml#L162-L192

• the code gets formatted in the process-resources phase
• the code format gets verified in the verify phase, so CI would fail
• the file headers are automatically added/updated/verified: https://github.com/gatling/gatling-maven-plugin/blob/main/pom.xml#L173

Regarding the code format to be adopted, spotless supports several of them.
IMHO, we should picking the default one, with no tuning, even if it doesn't match the current one. The point of code format conventions is to save time and headaches on endless and pointless personal preferences.
The code formatting would have to be applied on all 3 active branches to ease backporting.

WDYT?

[franz1981]

I am all in on this @slandelle ❤️

[chrisvest]

So basically you can always run a command locally to format things instead of waiting for CI to tell you what's been incorrectly formatted?

I often run a no-test build locally for checkstyle purpose, so this would be similar except it does the reformatting for me.

I'm not against it. Reformatting the three branches will be annoying, but we're only doing that once.

If IDEs can pick up the spotless formatting settings automatically, that would be a big benefit. Not clear if that's possible, though.

[slandelle]

So basically you can always run a command locally to format things instead of waiting for CI to tell you what's been incorrectly formatted?

You can do that, but as you would typically attach to process-resources which is the first phase of the maven lifecycle, it would trigger on most maven command you use in your workflow, including a basic mvn compile.

I often run a no-test build locally for checkstyle purpose, so this would be similar except it does the reformatting for me.

Exactly.

If IDEs can pick up the spotless formatting settings automatically, that would be a big benefit. Not clear if that's possible, though.

I haven't tried it, but there's indeed an IntelliJ IDEA plugin: https://plugins.jetbrains.com/plugin/22455-spotless-applier.
It seems you can also plug splotless as a git pre-commit hook.

Reformatting the three branches will be annoying, but we're only doing that once.

Indeed, it would be a one-time big bang.
But I think that's necessary for being able to cherry-pick backport commits across active branches.