Add native kotlin support

[vincentfree]

Kotlin support has been added to protobuf since version v3.17.0.
The generated kotlin files have kotlin dal support as an added bonus over direct usage of the java versions of the protobuf .java files

[vincentfree]

I have also updated the otel/build-protobuf image from version 0.4.0 to 0.7.0

[tigrannajaryan]

The new github action failed

[vincentfree]

The new github action failed

I will have to update the otel/build-protobuf image before this will pass since the current version of protobuf is quite old and does not support kotlin. I had a PR open for this so I'll fix those issues and hope It will make version 0.9.0. Afterwards this will also pass.

So this PR is dependend on: open-telemetry/build-tools#76

[vincentfree]

I have fixed the issue with the otel image locally. The builds are running and I hope this new functionality can be published soon so this PR can be finished and closed.

I've tested with the local build and got the compiled kotlin files, snippet:

kotlin/io/opentelemetry/proto/trace/v1:
total 100K
-rw-r--r-- 1 user root 2.0K Jan  8 09:13 ConstantSamplerKt.kt
-rw-r--r-- 1 user root 7.4K Jan  8 09:13 InstrumentationLibrarySpansKt.kt
-rw-r--r-- 1 user root 2.0K Jan  8 09:13 RateLimitingSamplerKt.kt
-rw-r--r-- 1 user root 8.1K Jan  8 09:13 ResourceSpansKt.kt
-rw-r--r-- 1 user root  45K Jan  8 09:13 SpanKt.kt
-rw-r--r-- 1 user root 2.4K Jan  8 09:13 StatusKt.kt
-rw-r--r-- 1 user root 7.6K Jan  8 09:13 TraceConfigKt.kt
-rw-r--r-- 1 user root    0 Jan  8 09:13 TraceConfigProtoKt.kt
-rw-r--r-- 1 user root 2.1K Jan  8 09:13 TraceIdRatioBasedKt.kt
-rw-r--r-- 1 user root    0 Jan  8 09:13 TraceProtoKt.kt
-rw-r--r-- 1 user root 7.1K Jan  8 09:13 TracesDataKt.kt

[bogdandrutu]

@vincentfree dependency merged, what else can I help with?

[vincentfree]

@bogdandrutu
Thanks, when the image is published then kotlin support should work and this PR can be updated with the new base image.

I've tested it on my laptop so I'm quite sure that this PR is almost done.

[bogdandrutu]

Can this depend on gen-java instead of re-generating the java files in their dir?

[vincentfree]

It could but there is a relation between the java and kotlin generated classes. The kotlin file 's refer to those from Java so it might work but I've never seen kotlin generation without the java_out option.

[vincentfree]

The reason why the build failed is because it has a dependency on the newer otel image with my other PR.

[bogdandrutu]

@vincentfree I understand the build failure, but still not sure about the regenerating of the java files in this rule. I would give a try without to see what happens :D

[vincentfree]

Doesn't hurt to try though the kotlin generation step would then have a dependency on the gen-java. Still it wouldn't have the overlap of files generated

[bogdandrutu]

With the latest update you need to change gen-openapi as well, no more swagger.

[vincentfree]

@bogdandrutu thanks for the new release of otel/build-protobuf:0.9.0
Updated the codebase with the new version, I'm now referencing gen-java in gen-kotlin so proper reuse ;)
And updated the swagger_out to openapiv2_out everything should be fine now.

I've tested gen-kotlin and gen-openapi locally. Both work.

[vincentfree]

@arminru your review is required to pass this PR. It's fully ready to merge back to main