Demo/proposal: FormattingFiler

[ZacSweers]

Inspired by GJF's implementation of the same name - this demos an implementation of a FormattingFiler that formats kotlin code with KtLint while writing. This could also be applicable to the other writeTo() overloads, but would require slightly different support.

I don't think this should be part of the first party KotlinPoet API, but it could be a useful extension artifact. This filer-only API alone may be more valid as an extension artifact on KtLint's project, but as mentioend above the implementation could be useful for other writeTo() overloads too.

Example usage:

val formattingFiler = filer.asFormatting()

fileSpec.writeTo(formattingFiler)

Possible other writeTo() overloads could be FileSpec.formattedWriteTo() extension functions, but would likely want to reuse the directory preparation logic.

Happy to also just put all this in a separate project and call it a day. Talked with @Egorand offline and wanted to give first refusal here :)

[JakeWharton]

For those who think kotlinc isn't slow enough?

[ZacSweers]

For those that generate models/etc in separate, heavily-cached non-gradle subprojects :)

[Egorand]

Agree that this shouldn't live in the main artifact, but we can definitely move this into a separate one. We do plan to improve Kotlinpoet's own formatting though.

[ZacSweers]

Do you want me to set up a separate artifact as part of this? Or discuss it further/separately first?

[ZacSweers]

I envision this to be more useful for consumers that are implementing possibly complex CodeBlocks, and not necessary as a replacement for KotlinPoet's own standard formatting for standard types :)

[Egorand]

Yep, let's set up a separate artifact.

[LouizFC]

We do plan to improve Kotlinpoet's own formatting though.

@Egorand could you elaborate please? Do you plan to use Kotlin official formatting guide as a base or this is just a backlog idea that isn't put much thought into?

[Egorand]

@LouizFC KotlinPoet already produces reasonably well-formatted code, but there are some issues we're aware of, such as function and constructor signature not being formatted according to the official style guide. This issue specifically is a top priority and I'm hoping to address it soon, if there's anything else that doesn't work for you - please file bugs.

[swankjesse]

I'd prefer to not fix our formatting bugs by introducing support for pluggable formatters. One thing we learned with Dagger 2 is that nobody wants to wait for a formatting step.

[ZacSweers]

Going to close this for now as I think the lack of any direct touch points with KotlinPoet means it probably should just be a separate project