Enable support for Kotlin/JS IR backend and introduce js_export parameter

[itegulov]

Fixes #136

I have tested js_export on my company's projects and it works pretty well. Obviously the resulting .d.ts declaration has some "red" parts as @JsExport does not support Kotlin collections, but overall it is still usable.

Let me know what you think and thanks for this amazing library!

[garyp]

Thanks for the PR @itegulov!

It looks like the build is failing in CI with a StackOverflowError from the Kotlin compiler. Unfortunately we've run into this many times with the new IR backend used by Kotlin/Native (and now available on JS and JVM too). It seems that the new IR backend is still buggy and certain Kotlin constructs in pbandk's source code will cause it to either use an inordinate amount of memory during compilation, or will cause it to get into an infinite loop. Both of which manifest as out-of-memory or stack overflow errors. You could try tweaking the jvmargs in gradle.properties to increase the memory available and see if that helps. If you can't replicate this when building on your own machine, try limiting the amount of memory available to the process to under 7GB. That's how much memory the CI job runs with.

I also see a bunch of warnings in the build log about non-exported types. Is this anything we need to worry about? E.g.:

w: /home/runner/work/pbandk/pbandk/runtime/src/commonMain/kotlin/pbandk/ExtendableMessage.kt: (10, 38): Exported declaration uses non-exportable parameter type: FieldDescriptor<M, T>

[itegulov]

@garyp Thanks for the review. StackOverflowError also happens occasionally on my local machine. Bumping -Xss to 512m seems to have resolved the issue for me locally, lets see how CI likes it... Also, due to the new Github rules and me being a first-time contributor, you need to give my PR a manual approval on Github Actions before any Actions workflows will run (see more here: https://github.blog/2021-04-22-github-actions-update-helping-maintainers-combat-bad-actors/).

I also see a bunch of warnings in the build log about non-exported types. Is this anything we need to worry about? E.g.:

Unfortunately, this is one of the short-comings of the @JsExport annotation: it does not fully support generics, Kotlin collections and any other custom classes that are not annotated with @JsExport. There is no way to get rid of those warnings completely without re-designing the API to be fully compatible with what @JsExport expects. So my take here is that it we should just ignore those warnings and hopefully @JsExport will be improved in the future. The generated Typescript declarations are still usable anyway, you just need to write a few custom utilities to e.g. convert between JS array and kotlin.collections.List or convert between JS objects and kotlin.collections.Map.

[itegulov]

@garyp the PR is ready from my perspective, could you take another look please?

[garyp]

A couple other things:

• CI is failing because you need to re-generate the code for the protobuf types that are bundled with pbandk and add those updates to your PR. This is the command to run:

./gradlew :runtime:generateWellKnownTypes \
    :runtime:generateTestTypes \
    :protoc-gen-kotlin:protoc-gen-kotlin-lib:generateProto \
    :conformance:conformance-lib:generateProto

• I ran the above command locally and then tried rebuilding the pbandk conformance tests and got a couple compiler errors:

> Task :conformance:conformance-lib:compileKotlinJs FAILED
e: /Users/gary/mydata/code/streem/pbandk/conformance/lib/src/commonMain/kotlin/pbandk/conformance/pb/test_messages_proto2.kt: (2571, 1): Declaration of such kind (extension property) cant be exported to JS
e: /Users/gary/mydata/code/streem/pbandk/conformance/lib/src/commonMain/kotlin/pbandk/conformance/pb/test_messages_proto2.kt: (2572, 5): JavaScript name (<get-extensionInt32>) generated for this declaration clashes with another declaration: fun <get-extensionInt32>(): FieldDescriptor<TestAllTypesProto2, Int?>
e: /Users/gary/mydata/code/streem/pbandk/conformance/lib/src/commonMain/kotlin/pbandk/conformance/pb/test_messages_proto2.kt: (2574, 1): JavaScript name (<get-extensionInt32>) generated for this declaration clashes with another declaration: fun TestAllTypesProto2.<get-extensionInt32>(): Int?

For the first error: I'm not sure if there's a way to tell Kotlin not to export a particular declaration when using @file:pbandk.Export at the file level? If there isn't, then we might need to drop the file-level annotation and go back to annotating each declaration that needs to be exported in the generated code.

For the second error: It's these two declarations that are conflicting with each other:

val pbandk.conformance.pb.TestAllTypesProto2.extensionInt32: Int? 
    get() = getExtension(pbandk.conformance.pb.extensionInt32)

val extensionInt32 = pbandk.FieldDescriptor(
    ...
)

They're both defining a getter on a field named extensionInt32. The first getter will have a receiver parameter in Javascript, whereas the second one won't, but they're otherwise named the same. So one of them will need an alternative name via @JsName. These two declarations are generated inside of the CodeGenerator.writeExtension() method.

[itegulov]

@garyp Unfortauntely, there does not seem to be a way to exclude declarations form a file-wide @JsExport. I have made it so that all top-level classes, orDefault methods and extension field descriptors are marked with @JsExport.

They're both defining a getter on a field named extensionInt32. The first getter will have a receiver parameter in Javascript, whereas the second one won't, but they're otherwise named the same. So one of them will need an alternative name via @JsName. These two declarations are generated inside of the CodeGenerator.writeExtension() method.

Actually, there is no need to give one of them a different name since the first one is an extension property that cannot be exported anyway.

[garyp]

Thanks again for the improvement!