Fix: Proguard/R8 configuration for createValueMap

[Sloy]

Description of the issue

The method com.segment.analytics.ValueMap#createValueMap uses reflection to create an instance of the given Class<T>. It expects a constructor receiving a Map.

Unfortunately, for some classes like Address, this constructor is not used anywhere else in the code so applications using Proguard or R8 to remove unused code will delete this constructor. The outcome is a runtime crash in the application.

Here's an example extracted from Firebase Crashlytics in our production application:

How to reproduce

We could not reproduce the exact same execution path of our crash, which goes through the AppboyIntegration library. But we can manually force the crash by invoking the getValueMap method:

Traits traits = new Traits();
traits.put("address", new ValueMap());
traits.getValueMap("address", Traits.Address.class);

It can be easily reproduced in the sample module by using the snippet above and enabling R8 in the analytics-samples/build.gradle file:

android {
  // ...
  buildTypes {
    debug {
      minifyEnabled true
    }
  }
}

The proposed fix

We implemented a workaround adding a Proguard rule into our application to stop it from removing code from the Segment SDK.

This PR aims to solve this issue for all consumers of the SDK by providing a consumerProguardFiles. The rule in this file keeps classes containing a constructor receiving a map. Proguard/R8 will keep the name of the class from obfuscation and the constructor from being removed.

I believe this is just enough to avoid similar crashes, but please double-check the solution.
Here's some more info about the setup:

• A library module may include its own ProGuard configuration file
• keepclasseswithmembers

[egor-n]

Would it make sense to update the "How should I configure my Proguard?" section now that the library provides built-in rules?

[prayansh]

@egor-n good call :) . I will make sure those are updated, if any changes are needed.

[sahilgarg90]

@egor-n good call :) . I will make sure those are updated, if any changes are needed.

https://segment.com/docs/connections/sources/catalog/libraries/mobile/android/android-faqs/#how-should-i-configure-proguard

I think this link needs to be update too, right?