升级Gradle后，Gson搭配Google Maps发布构建崩溃需哪些ProGuard规则？

问题现象 #

升级Gradle后，应用测试构建运行正常，但发布构建启动时直接崩溃，核心报错信息如下：

FATAL EXCEPTION: main
Process: com.richmondgamesstudio.foraging, PID: 22275 
java.lang.ClassCastException: com.google.gson.internal.l cannot be cast to com.google.android.gms.maps.model.LatLng
at com.richmondgamesstudio.foraging.Helper.l.b(Unknown Source:37) 
at y2.d.f(Unknown Source:448) 
at s2.b.onTransact(Unknown Source:89) 
at android.os.Binder.transact(Binder.java:1164) 
at fc.c(:com.google.android.gms.dynamite_mapsdynamite@225014047@22.50.14 (190800-0):2) 
at com.google.maps.api.android.lib6.impl.bg.run(:com.google.android.gms.dynamite_mapsdynamite@225014047@22.50.14 (190800-0):1) 
at android.os.Handler.handleCallback(Handler.java:942) 
at android.os.Handler.dispatchMessage(Handler.java:99) 
at android.os.Looper.loopOnce(Looper.java:201) 
at android.os.Looper.loop(Looper.java:288) 
at android.app.ActivityThread.main(ActivityThread.java:7872) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:936)

注释掉build.gradle中的minifyEnabled和shrinkResources后，发布构建可正常运行，说明崩溃由代码混淆/资源收缩机制导致。

现有Gson ProGuard配置 #

当前已配置的Gson相关混淆规则如下：

##---------------Begin: proguard configuration for Gson  ----------
# Gson uses generic type information stored in a class file when working with fields. Proguard
# removes such information by default, so configure it to keep all of it.
-keepattributes Signature

# For using GSON @Expose annotation
-keepattributes *Annotation*

# Gson specific classes
-dontwarn sun.misc.**
#-keep class com.google.gson.stream.** { *; }

# Application classes that will be serialized/deserialized over Gson
-keep class com.google.gson.examples.android.model.** { <fields>; }

# Prevent proguard from stripping interface information from TypeAdapter, TypeAdapterFactory,
# JsonSerializer, JsonDeserializer instances (so they can be used in @JsonAdapter)
-keep class * extends com.google.gson.TypeAdapter
-keep class * implements com.google.gson.TypeAdapterFactory
-keep class * implements com.google.gson.JsonSerializer
-keep class * implements com.google.gson.JsonDeserializer
-keep class * implements com.google.gson.GsonBuilder

# Prevent R8 from leaving Data object members always null
-keepclassmembers,allowobfuscation class * {
  @com.google.gson.annotations.SerializedName <fields>;
}

# Retain generic signatures of TypeToken and its subclasses with R8 version 3.0 and higher.
-keep,allowobfuscation,allowshrinking class com.google.gson.reflect.TypeToken
-keep,allowobfuscation,allowshrinking class * extends com.google.gson.reflect.TypeToken


##---------------End: proguard configuration for Gson  ----------

解决方案 #

在现有ProGuard规则中添加Google Maps LatLng类的保留配置，避免混淆破坏类结构导致Gson反序列化失败：

# 保留Google Maps LatLng类及其构造方法，确保Gson能正确反序列化
-keep class com.google.android.gms.maps.model.LatLng { *; }
-keepclassmembers class com.google.android.gms.maps.model.LatLng {
    <init>(double, double);
}

原因说明 #

开启混淆后，R8/ProGuard会对LatLng类进行优化（如重命名类/方法、移除未直接引用的构造方法），导致Gson在反序列化时无法识别目标类型，转而生成内部占位类com.google.gson.internal.l，最终抛出类型转换异常。添加上述规则可确保LatLng的类结构和构造方法完整保留，让Gson能正确完成反序列化。

内容的提问来源于stack exchange，提问作者JonR85