Moshi: Using Moshi 1.8.0 with R8 does not work with Json Qualifiers

[fmrsabino]

When we converted our project to use R8 our project started using the wrong Json adapter.

We have two qualifiers:

@Retention(AnnotationRetention.RUNTIME)
@JsonQualifier
annotation class HexNumber

@Retention(AnnotationRetention.RUNTIME)
@JsonQualifier
annotation class DecimalNumber

We then use these two qualifiers for the JsonAdapters:

class HexNumberAdapter {
    @ToJson
    fun toJson(@HexNumber hexNumber: BigInteger): String = hexNumber.toHexString()

    @FromJson
    @HexNumber
    fun fromJson(hexNumber: String): BigInteger = hexNumber.hexAsBigInteger()
}

class DecimalNumberAdapter {
    @ToJson
    fun toJson(@DecimalNumber bigInteger: BigInteger): String = bigInteger.toString()

    @FromJson
    @DecimalNumber
    fun fromJson(decimalNumber: String): BigInteger = decimalNumber.toBigInteger()
}

This is the class that specifies that the field is a DecimalNumber so DecimalNumberAdapter should be the one converting the field.

@JsonClass(generateAdapter = true)
data class Test(
    @Json(name = "payment") @field:DecimalNumber val payment: BigInteger,
)

When we switched to R8 (from ProGuard) the adapter that is triggered is HexNumberAdapter. My theory is that @field:DecimalNumber is removed when R8 kicks in thus Moshi will use the first adapter added (HexNumberAdapter).

We have the rules defined in this file.

Moshi Version 1.8.0 (using codegen).

[rmeissner]

We are creating moshi the following way:

return Moshi.Builder()
            .add(HexNumberAdapter())
            .add(DecimalNumberAdapter())
            .build()

also after adding the keep for the annotations explicitly it worked again (this was not required by proguard):

-keep @interface pm.gnosis.heimdall.data.adapters.HexNumber
-keep @interface pm.gnosis.heimdall.data.adapters.DecimalNumber

[ZacSweers]

Nothing else to be done here I think. These are used at runtime, so they need to be retained. Not sure why proguard didn't remove them compared to R8, as I expect it would as well unless it's trying to do some clever checks to guess if you're using it.

You could make a more general rule to keep all qualifiers via

-keep,allowobfuscation @com.squareup.moshi.JsonQualifier @interface * { *; }

[stairs]

Only the rule specified here worked for me after migrating to R8. I suggest updating documentation as the current rule for qualifiers: -keep @com.squareup.moshi.JsonQualifier interface * wasn't helpful for some reason.

[akhbulatov]

You could make a more general rule to keep all qualifiers via

-keep,allowobfuscation @com.squareup.moshi.JsonQualifier @interface * { *; }

It works, but shouldn't the next line from proguard-rules.pro of Moshi work in this case?
-keep @com.squareup.moshi.JsonQualifier interface *

[jkreiser]

Nothing else to be done here I think. These are used at runtime, so they need to be retained. Not sure why proguard didn't remove them compared to R8, as I expect it would as well unless it's trying to do some clever checks to guess if you're using it.

You could make a more general rule to keep all qualifiers via

-keep,allowobfuscation @com.squareup.moshi.JsonQualifier @interface * { *; }

This rule worked for me as well, whereas the -keep @com.squareup.moshi.JsonQualifier interface * rule did not.