I created a KotlinJS library for another team in m...

# javascript

[ade]

I created a KotlinJS library for another team in my org. Because of legacy reasons, they are linking the library twice in two separate js bundles. When either one runs separately it works fine, but if they load both bundles in the same js VM things start to behave strange. Is this a known limitation?

[CLOVIS]

What kind of weird behavior are you seeing?

But yeah, you're not supported to include the same code through multiple bundles, even in vanilla JS without using Kotlin

[Edoardo Luppi]

Wait, are you saying you have

PKG1
     \ K/JS lib
     / 
PKG2

And then they output

PKG1              BUNDLE1 
     \ K/JS lib /
     /          \
PKG2              BUNDLE2

And you load both bundles in Node/browser?

[Edoardo Luppi]

That's strange, why don't they bundle a single time?

[ade]

Yes @Edoardo Luppi that is correct it seems to be a pretty weird setup because they are migrating from an old app to a new tech stack. But sometimes the old techstack is the "parent page" and loads the new tech stack inside of it.

[ade]

Weird behaviour nr1: call to a regular suspend delay fails with

UnsupportedOperationException {message: 'third-party implementation of CancellableContinuation is not supported'

[ade]

Weird behaviour nr2: A kotlinx.serialization call to serialize a polymorph sealed class fails because it can't find the subclass serializer

[ade]

Serializer for subclass 'GoHome' is not found in the polymorphic scope of 'EndResult'.
Check if class with serial name 'GoHome' exists and serializer is registered in a corresponding SerializersModule. ...

[Edoardo Luppi]

I'm not sure if this applies to you too (are you running under Node or browser?), but I recall Coroutines write to the global `Window`: https://github.com/Kotlin/kotlinx.coroutines/issues/3874

[ade]

Yeah maybe! This is a webapp running in the browser

[ade]

Searching for the string "third-party implementation of CancellableContinuation is not supported" turns up only the source code itself making this pretty rare haha. My intuition is that there are two copies of CancellableContinuation and there is leakage between the instances of libraries so the class cast check fails

[Edoardo Luppi]

That's gonna be tough to workaround. You'll have to dissect the two bundles to understand how the compiled JS code works.

[Edoardo Luppi]

Could you post a screenshot of the outputted K/JS lib layout?

[ade]

From what viewer?

[Edoardo Luppi]

IntelliJ, under the dist/ folder

[ade]

image.png

[Edoardo Luppi]

Well, I would have supposed the Coroutines classes would be isolated in their own ES modules tbh.

[Edoardo Luppi]

Could you try recompiling with

kotlin.js.ir.output.granularity = whole-program

?

[ade]

Sure!

[Edoardo Luppi]

I don't think that it will change anything tho. The most likely issue is you're running bundled code in the browser with no module isolation.

[ade]

I've published it for them to consume, but I can't test it myself right now.

[Edoardo Luppi]

Let me know how it works, but I really doubt it's going to solve it.

[ade]

Thanks I will. We might need to load the lib in a smarter way and share it between the two apps.

[Edoardo Luppi]

I was just going to say that's the bundler's duty to fix this issue, maybe by splitting into chunks.

[turansky]

I was just going to say that's the bundler's duty to fix this issue

It depends on root cause of the problem

[turansky]

For example connection Promise <-> Deferred is unsafe now and should be fixed in coroutines

[Edoardo Luppi]

@turansky could you expand on the promise/deferred conversion? I wasn't aware of issues but good to know in case

[turansky]

If you will convert Deferred to Promise - result Promise will contain field deferred and it's unsafe - other Kotlin/JS applications can use it too 😞

[turansky]

In such situations private symbols should be used instead - for isolation reason.
"`Deferred` from other JS application - isn't my Deferred !"

[turansky]

If window contains magic string properties, created by coroutines - redundant conflicts are expected 😞

[Edoardo Luppi]

Ah yeah I was aware of that deferred property injected into the promise. Looking at the Git blame it's been there forever. I guess it was done as a potential optimization when converting back from the same promise.

[turansky]

I guess it was done as a potential optimization when converting back from the same promise.

It works fine with private symbol 😉

[turansky]

In Kotlin Wrappers we plan to migrate on private symbols

[ade]

Ok so we tried it (granularity = whole-program) and indeed it did not help.