Fix ProGuard config

[sk22]

I just temporarily disabled the "minifyEnabled" option in build.gradle to avoid all the crashes regarding #571 and released this as version 95 on the Play Store (the build is otherwise identical to version 94, and I think the build config is now actually equivalent with the config for the GitHub release).

Now ideally, of course, I'd like to re-enable ProGuard, but there appears to be some rules missing. (proguard-rules.pro is located here: https://github.com/sk22/megalodon/blob/main/mastodon/proguard-rules.pro)

Version 93's error message showed this stack trace:

Exception java.lang.ExceptionInInitializerError:
  at org.joinmastodon.android.GlobalUserPreferences.load (GlobalUserPreferences.java:95)
  at org.joinmastodon.android.MastodonApp.onCreate (MastodonApp.java:30)
  at android.app.Instrumentation.callApplicationOnCreate (Instrumentation.java:1211)
  at android.app.ActivityThread.handleBindApplication (ActivityThread.java:7094)
  at android.app.ActivityThread.access$1600 (ActivityThread.java:276)
  at android.app.ActivityThread$H.handleMessage (ActivityThread.java:2131)
  at android.os.Handler.dispatchMessage (Handler.java:106)
  at android.os.Looper.loopOnce (Looper.java:210)
  at android.os.Looper.loop (Looper.java:299)
  at android.app.ActivityThread.main (ActivityThread.java:8293)
  at java.lang.reflect.Method.invoke
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:556)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1045)
Caused by java.lang.RuntimeException: Missing type parameter.
  at com.google.gson.reflect.TypeToken.getSuperclassTypeParameter (TypeToken.java:84)
  at com.google.gson.reflect.TypeToken.<init> (TypeToken.java:62)
  at org.joinmastodon.android.GlobalUserPreferences$1.<init> (GlobalUserPreferences.java)
  at org.joinmastodon.android.GlobalUserPreferences.<clinit> (GlobalUserPreferences.java:65)

…which was resolved by adding the missing ProGuard rules for Gson:

# 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

Then, there was this error:

java.lang.ClassCastException: java.util.ArrayList cannot be cast to org.joinmastodon.android.model.HeaderPaginationList
	at org.joinmastodon.android.api.requests.HeaderPaginationRequest.validateAndPostprocessResponse(SourceFile:17)
	at org.joinmastodon.android.api.MastodonAPIController$1.onResponse(SourceFile:177)
	at okhttp3.RealCall$AsyncCall.execute(SourceFile:174)
	at okhttp3.internal.NamedRunnable.run(SourceFile:32)

…which could be resolved by adding this line:

# i don't know how proguard works
-keep public class * extends java.util.ArrayList

But this error is still unresolved:

java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to org.joinmastodon.android.model.Filter
	at org.joinmastodon.android.api.CacheController$$ExternalSyntheticLambda4.test(SourceFile:0)
	at j$.util.stream.Q1.accept(SourceFile:0)
	at j$.util.U.b(SourceFile:0)
	at j$.util.stream.c.p0(SourceFile:0)
	at j$.util.stream.c.Q0(SourceFile:0)
	at j$.util.stream.v0.H(Unknown Source:4)
	at j$.util.stream.c.T0(SourceFile:0)
	at j$.util.stream.W1.collect(SourceFile:0)
	at org.joinmastodon.android.api.CacheController.lambda$getHomeTimeline$3(SourceFile:61)
	at org.joinmastodon.android.api.CacheController.$r8$lambda$g-uVY2ox275rVKKmEKpWKndW6LA(SourceFile:0)
	at org.joinmastodon.android.api.CacheController$$ExternalSyntheticLambda2.run(SourceFile:0)
	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 me.grishka.appkit.utils.WorkerThread.run(SourceFile:54)

It seems to occur while it's trying to read the filters list,

List<Filter> filters = AccountSessionManager.getInstance()
    .getAccount(accountID).wordFilters.stream()
    .filter(f->f.context.contains(Filter.FilterContext.HOME)).collect(Collectors.toList());

which is loaded from the respective account.json file on startup (https://github.com/sk22/megalodon/blob/main/mastodon/src/main/java/org/joinmastodon/android/api/session/AccountSessionManager.java#L94, gson is initialized in https://github.com/sk22/megalodon/blob/main/mastodon/src/main/java/org/joinmastodon/android/api/MastodonAPIController.java#L52):

SessionsStorageWrapper w=MastodonAPIController.gson.fromJson(new InputStreamReader(in, StandardCharsets.UTF_8), SessionsStorageWrapper.class);
for(AccountSession session:w.accounts){
	domains.add(session.domain.toLowerCase());
	sessions.put(session.getID(), session);
}

[migdol]

After some tinkering (pulling the right commit for appKit, supply temporary signing credentials), I was able to compile the app. It didn't crash at launch for myself, but I did notice crashes when navigating to other portions of the app such as settings. The errors I witnessed involved instantiating Fragment classes in calls to Nav.go. I added the following to ProGuard to address this crash issue. It works by skipping Fragment classes during the minify and obfuscation step.

-keep class org.joinmastodon.android.**.*Fragment { *; }

For reference, I tested on a Pixel 6 emulator running API 33.

[sk22]

@migdol

-keep class org.joinmastodon.android.**.*Fragment { *; }

unfortunately, this didn't really seem to help.. most of the crashes happen after having restarted the app once - throwing this exception when loading (previously loaded and saved) filters:

java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to org.joinmastodon.android.model.Filter

anyway, seems like @LucasGGamerM's fix works fine (even though it just keeps everything). i think i'll just keep this line until i know what exactly i'd need to app to prevent the errors from happening

-keep class org.joinmastodon.android.** { *; }