Missing classes detected while running R8 / Proguard

[MarcelReiter]

Attempting to obfuscate and shrink any android app that uses Instant results in the following errors

Missing classes detected while running R8. 
Please add the missing classes or apply additional keep rules that are generated in
.../app/build/outputs/mapping/release/missing_rules.txt.

The file mentioned contains:

-dontwarn kotlinx.serialization.KSerializer
-dontwarn kotlinx.serialization.Serializable

To Reproduce

1. Create a new Android app.
2. Add the following dependency: implementation("org.jetbrains.kotlinx:kotlinx-datetime:0.4.0").
3. Create a new class which includes a field that is of type "Instant" and use it somewhere.
4. Attempt to obfuscate and shrink the app in release.

Minimal sample
See this github project: https://github.com/MarcelReiter/dateTimeTest
You NEED to build it in release mode.
Also i made nice small commits so it's understandable what i'm doing

Environment

• Kotlin version: 1.8.10
• Library version: 0.4.0
• Kotlin platforms: Android JVM

A nearly identical issue has been created by someone else in the kotlinx.serialization github:
Kotlin/kotlinx.serialization#2392 - but it seems like it is kotlinx.datetime related

[matejbart]

The current kotlinx.datetime version 0.4.0 is based on kotlinx.serialization version 1.3.2, so one option is to explicitly bump the kotlinx.serialization version to the latest stable version 1.5.1 that already contains the proguard rules (see release notes v1.5.0-RC) to fix these issues.

[ilya-g]

@matejbart Not sure it would help. kotlinx-serialization is used as a compile time dependency in JVM variant of kotlinx-datetime and therefore is not propagated transitively to dependees, so it's irrelevant which rules it contains.

[MarcelReiter]

I have updated to kotlinx.datetime 0.4.1 which includes an update of kotlinx.serialization to 1.5.1.
However, the issue still exists. Can someone confirm?

[VitaliyBelyaev]

I have updated to kotlinx.datetime to 0.5.0 which uses kotlinx.serialization 1.6.2 as I see in External libraries section in Android Studio, but issue with R8 still exists.

• Android Studio Hedgehog | 2023.1.1 RC 1
• Kotlin 1.9.21
• Android Gradle Plugin 8.2.0

[VitaliyBelyaev]

As workaround, I've added kotlinx.serialization explicitly to the project: plugin and dependency version 1.6.2 to the android app and issue with R8 gone.

I think that proguard rules from kotlinx.serialization were applied and that fixed issue.

Maybe some or all rules from kotlinx.serialization should be added to kotlinx.datetime library for those who needs kotlinx.datetime but don't uses kotlinx.serialization.

[ilya-g]

I've added kotlinx.serialization explicitly to the project: plugin and dependency version 1.6.2 to the android app and issue with R8 gone.
I think that proguard rules from kotlinx.serialization were applied and that fixed issue.

The workaround helped because the classes that R8 reported as missing are now found in the kotlinx.serialization dependency you've added.