Hi everyone :wave: I'm currently experimenting KMP...

# swift-export

[Arnaud Schildknecht]

Hi everyone 👋
I'm currently experimenting KMP with Swift Export and I've been struggling with an issue. Let me explain 🙂
I've setup a small project with the following configuration :

├── androidApp/
├── iOSApp/
└── shared/
	|
	├── core/
	|	└── build.gradle.kts
	└── feature/
		|
		├── featureA/
		|	└── build.gradle.kts
		└── featureB/
			└── build.gradle.kts

Each build.gradle file makes the module available for Swift and Android with something like:

kotlin {
	android {
		namespace = "..."
		...
	}

	@OptIn(ExperimentalSwiftExportDsl::class)
	swiftExport {
		moduleName = "..."
		flattenPackage = "..."
	}
}

Then I try to compile the iOS project and I get errors such as :

Unable to resolve module dependency: 'ExportedKotlinPackages'
Unable to resolve module dependency: 'KotlinRuntimeSupport'

I've managed to reproduce the problem with the official sample, by adding the android directive to any of the module (shared, module-a and module-b). It looks like swiftExport and android can't be declared in the same module.
At the end, I managed to fix the problem by creating an umbrella module, which does the swift export for every modules, only letting the android app use directly the other modules. Is it a known issue, or it might be normal? The way to structure a KMP project with Swift Export seems to be different to the Obj-C export.
Is using an umbrella module the right solution? Why can't I export a module directly for Android and Swift?

[Artem Olkov]

Hello there! Thanks for the report 🙂

I was unable to reproduce the problem based on the description provided. Please see the modified version of the sample, where I try to reproduce the problem. Please either tell me what I'm missing, or provide me with a fork/branch that reproduces the problem 🙂

Each build.gradle file makes the module available for Swift

That is not correct. With swift export umbrella module is not gone - the whole world compilation model on the side of kotlin compiler is still there. With swift export project structure on the side of KMM should be the same - an umbrella module defining what and how would be exported.

The way to structure a KMP project with Swift Export seems to be different to the Obj-C export.

Nope, the recommended structure for both of the exports is the same 🙂
kotlinlang.org/docs/multiplatform/multiplatfor…#…

Is using an umbrella module the right solution?

Yes, it is

Why can't I export a module directly for Android and Swift?

You can. Each kotlin klib/project would be exposed to swift and swift would see it as a separate module. Umbrella module on the side of KMP is a project that defines the nuances of what and how should be built, and what and how should be exposed.

[Arnaud Schildknecht]

I don't have the exact same project anymore, as I was pushing the experiment.
But I might have an idea of what could be going on.

I'm modularising the iOS app, using a modular architecture such as Tuist's TMA. It means that each feature is an xcodeproj. I initially added the same same script to each feature (./gradlew :sharedKit:embedSwiftExportForXcode), so I think the problem is that the shared bit is compiled many times instead of one. See the attached example swift-export-tma.

I've introduced an umbrella framework in the iOS app, which is only responsible to bridge the shared bit with the iOS app, making the shared code compiled only once, then used by the features requiring it. I'm still looking into how to setup my iOS project properly, because I keep getting these kinds of errors and I don't really get why.

swift-export-tma.zip

[Artem Olkov]

``embedSwiftExportForXcode`` should be called only once, from the "host" target 🙂

We do not have documentation on how to integrate KMP with Tuist, sorry, I don't have a quick guide to show to you. But umbrella module is a way to go 🙂

[Arnaud Schildknecht]

Yeah no worries, I understand 🙂
Just a quick question about

``embedSwiftExportForXcode`` should be called only once, from the "host" target

Is it mandatory to call it from the host target? Or it can be called only from an "bridge" framework?
For example :

├── iOSApp/
    ├── iOSApp/           // Host app. Dependency with sharedBridge
    |    └── iOSApp.swift
    ├── feature/
    |    ├── featureA/    // Dependency with sharedBridge
    |    └── featureB/    // Dependency with sharedBridge
    └── sharedBridge/     // Framework bridge to the KMP shared module => calls embedSwiftExportForXcode

[Artem Olkov]

IIUC your setup - yes, calling it from shared bridge should be fine 🙂

[Arnaud Schildknecht]

Well, it doesn't seem to be working when running the gradle task from a xcode framework 😕
Something should be missing either with my configuration or inside the gradle task. It seems not able to find ExportedKotlinPackages and KotlinRuntimeSupport and I can't point the finger on what's missing.

[Artem Olkov]

Can you please provide a demo project for that? It would grately simplify the debugging 🙂

[Arnaud Schildknecht]

Here is a demo.
The iOS project is initialised. You should be able to open the workspace and compile directly.
You can try to compile the target "SharedBridge" as it's the one running the gradle task. The host app is importing SharedBridge.
I've simplified the dependency graph by commenting some of the shared dependency in order to keep it as simple as possible.
Let me know if you have any issue with the sample.

tma-tuist-kmp-sample.zip

[Arnaud Schildknecht]

I just realised I left kotlin version 2.4.20-Beta2 in the sample. I used 2.4.10 most of the time and I got the same error.
It's just that I get another error with the Beta version (related to Koin), but if you get there, it means you fixed the issue 😛

[Arnaud Schildknecht]

Was it any helpful? 🙂

[Artem Olkov]

Hello there. Sorry, I got lost in day to day task.

I looked at this problem and it's a duplicate of this - youtrack.jetbrains.com/issue/KT-80346

Basically the problem is that you are targeting swift export to a library target inside xcode project and not the application target.