CODEWITHSUNDEEP
androidkotlinproguardmoshiandroid-r8
der_Fidelis
der_Fidelis

Reputation: 1515

Prevent proguard/r8 from removing Kotlin synthetic default constructor

I'm using moshi which accesses the Kotlin default constructor of a class by reflection.

The class looks like this:

@JsonClass(generateAdapter = true)
data class AClassName(
    val threadId: String,
    val title: String? = null
)

If I use "View bytecode" in Android Studio I can see the constructor does in fact exist:

public synthetic <init>(Ljava/lang/String;Ljava/lang/String;ILkotlin/jvm/internal/DefaultConstructorMarker;)V

To try and keep it I add

-keep @com.squareup.moshi.JsonClass class * {
    <init>(...);
}

However, r8 removes it anyway, keeping only the non-synthetic constructor. Does anyone know why?

Upvotes: 1

Views: 504

Answers (1)

sgjesse
sgjesse

Reputation: 4628

From what I can see R8 keeps the Kotlin default constructor when using the shown rule. However, it also renames the type kotlin.jvm.internal.DefaultConstructorMarker, as there is no keep on that class, so after R8 there are the DEX contains the following two constructors:

.method public constructor <init>(Ljava/lang/String;Ljava/lang/String;)V
.method public synthetic constructor <init>(Ljava/lang/String;Ljava/lang/String;ILb/a;)V

Adding -keep on the marker class

-keep,allowshrinking class kotlin.jvm.internal.DefaultConstructorMarker

results in the following methods in the DEX:

.method public constructor <init>(Ljava/lang/String;Ljava/lang/String;)V
.method public synthetic constructor <init>(Ljava/lang/String;Ljava/lang/String;ILkotlin/jvm/internal/DefaultConstructorMarker;)V

Which I assume is what you are looking for.

If there are default values for all properties

data class AClassName(
    val threadId: String = "",
    val title: String? = null
)

or an explicit empty constructor

data class AClassName(
    val threadId: String,
    val title: String? = null
) {
  constructor() : this("", null)
}

you will also get the Java no-args constructor:

.method public constructor <init>()V

Upvotes: 1

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