Add support for repeatable annotations

[YangSiJun528]

Resolves issue #1624 by adding support for multiple annotations of the same type.

Key changes:

• Allows AnnotationContainer to support multiple annotations
• Fixes KotlinSourceCodeWriter#writeProperty to correctly write annotations
• Adds tests for repeated annotations

Fixes gh-1624

[mhalbritter]

Hello! The build is failing because of formatting violations. You can check them locally by running ./mvnw verify.

[YangSiJun528]

I made the fix and confirmed it works locally.

[mhalbritter]

Hello,

thanks for the PR! I might have missed something here, but why did you create a second implementation for the annotations? Is there a reason we couldn't add the functionality for repeated annotations into the AnnotationContainer itself?

[YangSiJun528]

After thinking more about your previous comment, I realized there might be a better approach that allows AnnotationContainer itself to support repeated annotations.
This way, it adds support for repeatable annotations without many code changes.

You can see it in this commit — I've confirmed that it doesn't break any existing tests:
YangSiJun528@488ce5a

Sorry if my earlier proposal ended up taking unnecessary time.

Do you think this approach would be better?
If you agree, I can update the PR with this version.

[mhalbritter]

Yes, please update the PR. Thanks!

[YangSiJun528]

I've updated the PR. @mhalbritter

[mhalbritter]

I don't really like the concept of an annotation name. What do you think about deprecating the add methods, and add two new methods: addSingle and addRepeatable.

addSingle behaves essentially like add but if there is more than one annotation of the given class and a customizer is provided it fails. Also addSingle doesn't add a annotation if it's already there.

addRepeatable can't customize already existing annotations, it always adds a new one.

[YangSiJun528]

I thought AnnotationContainer needed a key to identify specific annotations when there are multiple ones of the same type.

But you're probably right that the annotation name concept adds unnecessary complexity.

So you're suggesting addSingle/addRepeatable would be cleaner because most use cases don't need to handle specific instances of repeatable annotations?

[mhalbritter]

I find the existing add method somewhat confusing in that it either adds or modifies the existing one. That behavior is not applicable to repeatable annotations.

We could also think about adding:

• addSingle (fails if there is already one of the same type)
• addRepeatable
• addSingleOrCustomize (essentially the existing add method - but fails if there are multiple annotations of that type registered already. Allows to customize the annotation if there is one already).

I have to play around a bit.

[mhalbritter]

One more data point to split the functionality from add and customize: io.spring.initializr.generator.buildsystem.gradle.GradleConfigurationContainer has separate add and customize methods.

[mhalbritter]

However, io.spring.initializr.generator.buildsystem.gradle.GradlePluginContainer also combines add and customize. Hm.

[YangSiJun528]

Actually, customize might be a fine name too.
From a ClassName perspective, customize and replace seem to have similar meanings.

[mhalbritter]

I arrived at this api, what do you think?

https://github.com/mhalbritter/initializr/blob/mh/repeatable-annotations/initializr-generator/src/main/java/io/spring/initializr/generator/language/AnnotationContainer.java

[YangSiJun528]

Looks good!
I think this is much cleaner than the previous implementation.

I found that single annotations have customize functionality, but repeatable annotations don't.
Do you think repeatable annotations should also have customize features like single annotations do?

If so, methods like customizeAllRepeatable, customizeRepeatableIf, or removeRepeatableIf might be helpful for more granular control over repeatable annotations.

What do you think? Should I look into adding these features?

[mhalbritter]

Thanks for looking at it. Do you want to take this code into your PR?

I don't think customizing repeatable annotations make sense. We can add this functionality later, if the need arises.

[YangSiJun528]

Okay, I'll update the PR based on the code you provided and mention you.