Add Kotlin Web (Ktor & KotlinJS) examples (1650USD Bounty)

[lihaoyi]

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From the maintainer Li Haoyi: I'm putting a 1650USD bounty on this issue, payable by bank transfer on a merged PR implementing this.

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The goal of this ticket is to implement support for example/kotlinlib/web example tests for using Kotlin for web development, mirroring the example/javalib/web and example/scalalib/web, and support for KotlinJS in the spirit of scalajslib/. I would want the following example tests, broken down into smaller groups each with its own bounty:

650USD:

• example/kotlinlib/web/1-hello-ktor
  • A hello-world example using Kotlin and KTor to set up a web server serving a single "<h1>Hello, World!</h1>" web page, in the spirit of example/javalib/web/2-hello-spring-boot
• example/kotlinlib/web/2-todo-ktor
  • An implementation of the common TodoMVC demo application, including HTML templating, JS/CSS resources, database access and unit/integration/runBackground+curl tests, in the spirit of example/javalib/web/3-todo-spring-boot

650USD:

• example/kotlinlib/web/3-kotlinjs-module (325USD)
  • How to define a simple KotlinJS module that can be compiled to Javascript, testing, and run using node, in the spirit of example/scalalib/web/3-scalajs-module
• example/kotlinlib/web/4-webapp-kotlinjs (325USD)
  • How to wire up a KotlinJS module with a Kotlin/Ktor server to serve the generated Javascript, in the spirit of example/scalalib/web/4-webapp-scalajs

700USD:

• example/kotlinlib/web/5-webapp-kotlinjs-shared (350USD)
  • How to implement code sharing between a JVM KTor server and a KotlinJS javascript module, such that common code and utilities can be used by both. In the spirit of example/scalalib/web/5-webapp-scalajs-shared,
• example/kotlinlib/web/6-cross-platform-publishing (350USD)
  • How to define a library with both Kotlin-JVM and Kotlin-JS versions and publishing it to maven central. In the spirit of example/scalalib/web/6-cross-version-platform-publishing
  • Moving this to a separate bounty

Each of these examples above has a corresponding javalib/scalalib equivalent, and it should generally follow the style of those equivalents (scope, testing, etc.) but translated to Kotlin (Java/Scala -> Kotlin, Scalajs -> Kotlinjs, Cask/SpringBoot -> KTor, etc.)

For now the Kotlin-JS logic should live in kotlinlib/ together with the rest of the kotlin-specific configuration.

[c0d33ngr]

Let me try if I can do anyone

[c0d33ngr]

Hello, I'm new here.
How do I run the tests in the examples directory? mill testin where build.mill file is located output

build.sc file not found. Are you in a Mill project folder?

[lihaoyi]

@c0d33ngr please see the readme.md at the root of the repo

[0xnm]

I did a quick overview of the things which should be done here, and it seems that the work can be sliced in a bit more granular way.

The main complexity here comes actually from implementing Kotlin/JS support (similar to the Scala/JS) which is itself a quite big task, because:

• There are 2 modes here: only module content output (may be the case for libraries) or a complete output with Kotlin runtime and other libraries included (basically output with linking applied) - this is the case for the executable output.
• What about the NPM modules support (Kotlin/JS supports it)? I don't think it should come in the initial version, but it is a quite handy feature.
• Different module kind support (should be just a configuration flag, I hope, though).

So I think maybe implementing Kotlin/JS support is worth to be extracted into a different task? Making examples is easier than that.

Also this raises a design question: say there is a code which should be compiled to both JVM and JS targets. How this could be done with existing Scala modules, for example? I believe ScalaModule and ScalaJSModule cannot be declared for the same module at the same time, because of the conflicting declarations (ScalaJSModule extends ScalaModule).

[lihaoyi]

@0xnm as written, the KotlinJS stuff (bullets 3-6) is already in separate milestones from the pure Ktor/web stuff (bullets 1-2). Bullets 3 and 6 seem pretty independent of Ktor and should be doable without any pre-requisites, and bullets 1-2 should be independent of KotlinJS. I don't mind adding more non-KotlinJS web stuff, just not sure what that would entail.

In Scala-land, cross-platform Scala code is normally handled via PlatformScalaModule, which defines multiple sub-modules for .jvm .js (and maybe .native) that share the same code. Thus the code ends up being compiled multiple times by the different versions of the Scala compiler. KotlinJS/KotlinJVM could use the same approach, or if they have any other techniques for cross-platform code we could use their thing as well.

I'm hoping the KotlinJS tooling already has a decent API/CLI, and most of the work would just be wiring it into Mill. I'm not sure how true that actually is, but as a point of reference Mill's ScalaJS support is 14 files and 1600 lines of code with another 1000 lines of tests for basically 100% coverage of ScalaJS' functionality. I'm hoping KotlinJS won't be that much more work, but I don't know

The bounty amounts are pretty arbitrary TBH and are just my best guess w.r.t. the amount of work necessary. For the KTor stuff they should be pretty reasonable, since those bullets shouldn't require any special tooling background. But if we think the KotlinJS bounties aren't proportionate to the amount of work necessary, I can totally bump them up, or if someone wants a different arrangement (e.g. some payment up front to de-risk the effort )

[0xnm]

I added a very basic PR with a foundation for Kotlin/JS support in #3678, but there are many issues/missing functionality. See that PR for more details.