Provide consumer Proguard rules for Android

[ntsik]

Android provides a way for libraries to package their own Proguard rules such that users of the library don't need to add rules explicitly. Having consumer rules available simplifies the upgrade process (devs currently need to remember to upgrade the Proguard rules alongside the library version).

[sandwwraith]

This can't be done fully on library's side, unfortunately — some proguard rules have to be rewritten using an actual package name of the application

[ntsik]

I had a feeling that might be an impetus, though I wasn't sure whether there was some way to work around that. Maybe adding an annotation to the generated code that Proguard can target? (I'm not very familiar with the inner workings of the library or Proguard, so not sure how feasible it would actually be.)

[ArcticLampyrid]

One possible solution

Mark the gen code with specific annotations and add rules to keep all the classes with annotations

[ArcticLampyrid]

In fact, android defines Keep annotation
Of course, the pre-defined annotation is android-only, we need to define it by ourselves

[ArcticLampyrid]

My rules:

-keepattributes *Annotation*, InnerClasses
-dontnote kotlinx.serialization.AnnotationsKt
-keepclassmembers @kotlinx.serialization.Serializable class ** {
    *** Companion;
}
-if @kotlinx.serialization.Serializable class **
-keepclassmembers class <1>$Companion {
    kotlinx.serialization.KSerializer serializer(...);
}
-keepclasseswithmembers class **$$serializer {
    *** INSTANCE;
}

See Also #1129

[mxalbert1996]

I'm against this proposal as I said in #1129:

Obfuscation is important to me and is actually one of the reasons I migrated from Moshi as the Moshi codegen generates ProGuard rules that prevent obfuscation. I don't think there is any ways to exclude part of the rules from libraries, so I would prefer not embedding the rules as they are intrusive (they affect user code and cannot be disabled).

Actually I'm specifying the serializers of all json classes in my project manually so that I don't need any proguard rules.

[ArcticLampyrid]

Actually I'm specifying the serializers of all json classes in my project manually so that I don't need any proguard rules.

Perhaps we can use a clever compiler plugin to detect serializer staticly in most cases.
Anyway, we need to simplify the consumer's work on Android with obfuscation enabled (default on Android).

[LouisCAD]

Hello, I bumped into runtime crashes because the rules are not bundled.

@sandwwraith most of the rules don't depend on the package of the models, so all these rules could be bundled, which would make the setup much easier as only app-specific rules would need to live in the end codebase.

Even better than that, since @Whathecode edits in #1721, it turns out you'd not need custom proguard/R8 rules at all, unless you have custom named companion objects, which is quite a rare thing AFAIK.

See one of the files provided by kotlinx.coroutines for that:

https://github.com/Kotlin/kotlinx.coroutines/blob/master/kotlinx-coroutines-core/jvm/resources/META-INF/proguard/coroutines.pro

Shall I send a PR adding those files?

[Whathecode]

Note that the reason they weren't bundled yet is:

The following configuration keeps serializers for all serializable classes that are retained after shrinking.
...
In case you want to exclude serializable classes that are used, but never serialized at runtime, you will need to write custom rules with narrower class specifications.

But arguably that's enough of an edge case to simply apply the generic rules by default. You should consider the tradeoff with how difficult it potentially is to remove the default bundled rules (I don't know), and possibly document that as well.

[sandwwraith]

I've looked at current suggested proguard rules, and it seems that most of them don't include an application package indeed. So yes, embedding rules is possible. And of course, I would be happy to see your PR!

[sandwwraith]

Also pls take a look at this comment: #2050 (comment)
It seems that full mode needs additional rules