Obfuscate Android app warning Play Console

The message is just a warning which suggests you to obfuscate your code so that it is not visible by reverse engineering the source code. Being a warning you will be able to upload your application without problem.

Warning This APK contains Java or Kotlin code, which can be obfuscated. We recommend that you upload a deobfuscation file to facilitate analysis and debugging of ANR errors and crashes. More information

This is done with the following configuration, mainly the property minifyEnabled true:

android {
    buildTypes {
        release {
            // Enables code shrinking, obfuscation, and optimization for only
            // your project's release build type.
            minifyEnabled true

            // Enables resource shrinking, which is performed by the
            // Android Gradle plugin.
            shrinkResources true

            // Includes the default ProGuard rules files that are packaged with
            // the Android Gradle plugin. To learn more, go to the section about
            // R8 configuration files.
            proguardFiles getDefaultProguardFile(
                    'proguard-android-optimize.txt'),
                    'proguard-rules.pro'
        }
    }
    ...
}

Check out: How to shrink, obfuscate, and optimize your app

You must create your file to obfuscate code and to upload it, you do it from the Google Play console , select the application and from "Releases overview", you can review the latest releases or search by version, and click on the blue arrow:

Inside the "App bundles and APKs" section, click on the 3-dot symbol to access the "Upload ReTrace mapping file (.txt or .map)" option, this is where you will upload your file.

You shouldn't need to upload any files. You just have to activate the minification:

minifyEnabled true
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'

Traditionally this enabled proguard but as of version 3.4.0 of the Android Gradle plugin it was replaced by R8. This is the new code shrinker developed by google and optimized for android. It has two main tasks:

• obfuscation - Rename all classes, properties, and methods to the shortest name possible. Although this is normally called obfuscation, it is more appropriately called minification because your code is still readable.
• shrinking: removes all classes, properties and methods that are apparently not used.

Although R8 is a new compiler, it uses the same settings as proguard. These settings are found in files defined in gradle as proguardFiles:

• "proguard-android-optimize.txt": This is included in the android tools and you should not touch it.
• "proguard-rules.pro": These are settings specific to your project. Here you can do things like keep the names of the classes you use as firebase models.

However, there are easier ways to do it. For example you can use the annotation @Keepso that R8 does not modify a class.

@Keep
class Example(
    var foo: String? = null,
    var bar: Int? = null
)

Another alternative is to use @PropertyNamefirebase annotation.

class Example(
    @PropertyName("foo") var foo: String? = null,
    @PropertyName("bar") var bar: Int? = null
)

This way you won't have any problems when names are shortened as firebase will use the annotation string instead of the property name.