:wave: Is it possible to write a compiler plugin t...

# compiler

[eekboom]

👋 Is it possible to write a compiler plugin that adds a Builder pattern a la lombok's @Builder?
I understand that it's not needed if you stay in the Kotlin world, but for migrating a large codebase that uses lombok to Kotlin, it would help a lot if you could use builders in Java to create instances of Kotlin classes.

[eekboom]

Thanks for the MVA (minimal viable answer) 😄
I'll try to dig my way through the scarce docs and articles.

[eekboom]

BTW: A testing framework in Kotlin similar to Spock would be awesome, but that would require expert understanding of compiler plugins and a whole lot of effort, I guess.

[raulraja]

here is an example that shows how to deal with IR to inject calls and perform implicit instantiations for a proof system https://github.com/arrow-kt/arrow-meta/blob/master/compiler-plugin/src/main/kotlin/arrow/meta/plugins/proofs/phases/ir/ProofsIrCodegen.kt
In your case you’d have to work with similar APIs if your plugin targets the IR backend.

[raulraja]

The notion is that you’d define what @Builder does and in the IR phase transform the tree to a new tree which includes whatever boilerplate you want to inject

[eekboom]

Thanks a lot! Let's see how far I get.

[raulraja]

The key piece is parts like this https://github.com/arrow-kt/arrow-meta/blob/master/compiler-plugin/src/main/kotlin/arrow/meta/plugins/proofs/phases/ir/ProofsIrCodegen.kt#L14[…]L152 where you can see that an initializer or dispatch receiver of an expression can be mutated and changed allowing you to alter the tree before it turns into bytecode

[Sasha Shpota]

I believe you can implement Builder even without a compiler plugin. It is also achievable with annotation processing. But it is certainly possible with a compiler plugin

[eekboom]

@Sasha Shpota Yes, you can - kinda.
See https://github.com/ThinkingLogic/kotlin-builder-annotation
For full support of these, I suspect you need a compiler plugin:
• default values
• nullability
• mutability of collections
• lombok-like SomeClass.builder() method
Besides, I just want to try it for fun 🙂