AGP 8.2与Java17迁移中Retrofit+Kotlin序列化混淆问题

将Android Gradle Plugin(AGP)从7.4.2升级到8.2、Java版本从11升到17后，Retrofit接口调用出现混淆错误：
Unable to create @Body converter for class package.api.data.device.DevicesBody (parameter #1) for method a.a

项目使用Retrofit 2结合Kotlin Serialization(kotlinx.serialization)，除API调用外其他功能正常。禁用混淆（minifyEnabled false）或添加全保留规则（-keep class ** { *; }）能临时解决，但不符合代码优化要求。

相关代码 #

private val json = kotlinx.serialization.json.Json {
    prettyPrint = true
    ignoreUnknownKeys = true
    explicitNulls = false
}
private val contentType =  "application/json".toMediaType()
private val retrofit: Retrofit by lazy {
    Retrofit.Builder()
        .addConverterFactory(json.asConverterFactory(contentType))
        .baseUrl(baseUrl)
        .client(httpClient)
        .build()
}

@Keep
@Serializable
data class DevicesBody(
    @SerialName("dh_info")
    val dhInfo: DhInfo
)

@Keep
@Serializable
data class DhInfo(
    @SerialName("type")
    val type: String,
    @SerialName("value")
    val value: String
)

@POST("devices")
suspend fun postDevice(@Body requestBody: DevicesBody): Response<DevicesResponse>

异常信息 #

MESSAGE: Unable to create @Body converter for class {my_package}.api.data.device.DevicesBody (parameter #1) for method a.a
STACKTRACE:
    [retrofit2.Utils.methodError(Utils.java:54),
    retrofit2.Utils.parameterError(Utils.java:60),
    retrofit2.RequestFactory$Builder.parseParameterAnnotation(RequestFactory.java:781),
    retrofit2.RequestFactory$Builder.parseParameter(RequestFactory.java:325),
    retrofit2.RequestFactory$Builder.build(RequestFactory.java:206),
    retrofit2.RequestFactory.parseAnnotations(RequestFactory.java:67),
    retrofit2.ServiceMethod.parseAnnotations(ServiceMethod.java:26),
    retrofit2.Retrofit.loadServiceMethod(Retrofit.java:202),
    retrofit2.Retrofit$1.invoke(Retrofit.java:160),
    java.lang.reflect.Proxy.invoke(Proxy.java:1006),
    $Proxy5.a(Unknown Source), g0.j0.invokeSuspend(SourceFile:1),
    g0.j0.invoke(SourceFile:1), c.g.a(SourceFile:0),
    g0.k0.invokeSuspend(SourceFile:0),
    g0.k0.invoke(SourceFile:1),
    kotlinx.coroutines.flow.SafeFlow.collectSafely(Builders.kt:61),
    kotlinx.coroutines.flow.AbstractFlow.collect(Flow.kt:230),

AGP 8.2迁移改动 #

1. app/build.gradle #

dependencies {
    classpath "com.android.tools.build:gradle:8.2.0"
}

compileOptions {
    sourceCompatibility JavaVersion.VERSION_17
    targetCompatibility JavaVersion.VERSION_17
}

kotlinOptions {
    jvmTarget = '17'
}

2. gradle-wrapper.properties #

distributionUrl=https\://services.gradle.org/distributions/gradle-8.2-bin.zip

3. gradle.properties #

# Enable generation of the BuildConfig class
android.defaults.buildfeatures.buildconfig=true
# Disable on-transitive R classes
android.nonTransitiveRClass=false
# Disable R classes with non-final fields
android.nonFinalResIds=false

4. app/proguard-rules.pro #

# Keep generic signature of Call, Response (R8 full mode strips signatures from non-kept items).
-keep,allowobfuscation,allowshrinking interface retrofit2.Call
-keep,allowobfuscation,allowshrinking class retrofit2.Response

# With R8 full mode generic signatures are stripped for classes that are not
# kept. Suspend functions are wrapped in continuations where the type argument
# is used.
-keep,allowobfuscation,allowshrinking class kotlin.coroutines.Continuation

解决方案 #

AGP 8.2配套的R8混淆规则更严格，即使给数据类添加了@Keep注解，Kotlin序列化所需的元信息仍可能被剥离。需在app/proguard-rules.pro中添加以下规则，保留API数据包下的所有类和枚举：

...
# 保留API数据类，确保Kotlin序列化正常工作
-keep class {my_package}.api.data.** { *; }
-keep public enum {my_package}.api.data.** { *; }
...
# Retrofit2原有规则保留
# Keep generic signature of Call, Response (R8 full mode strips signatures from non-kept items).
-keep,allowobfuscation,allowshrinking interface retrofit2.Call
-keep,allowobfuscation,allowshrinking class retrofit2.Response
# With R8 full mode generic signatures are stripped for classes that are not kept. Suspend functions
# are wrapped in continuations where the type argument is used.
-keep,allowobfuscation,allowshrinking class kotlin.coroutines.Continuation

内容的提问来源于stack exchange，提问作者romainb78