Optimize Proguard rules (#4291)

Using saner defaults for R8 while reducing the app size even further.
- Add Kotlin compiler options to skip adding assertions in release
builds
- Remove `optimizations`, `optimizationpasses` and `dontpreverify` rules
that are ignored by R8
- Only keep runtime annotations by default. If other attributes are
needed by a specific library, these will already be provided by the
library rules (for example Retrofit or coroutines)
- Remove the obsolete rule allowing a View to reflectively call any
arbitrary public Activity method accepting a View as argument. This has
always been a bad practice and is not used in this project anyway
- Remove the rules related to enums. R8 already optimizes enums properly
out-of-the-box and keeping these rules may prevent some of these
optimizations
- Add support for the `@Keep` annotation. Even if it's not currently
used in the code base, it can be handy in the future
- Add a missing rule to prevent generic signature of `NetworkResult`
class from being removed in `MastodonApi` so Retrofit works
- Allow obfuscation and shrinking of `kotlin.coroutines.Continuation`,
matching the rule defined in the next release of Retrofit
- Remove the rule forcing the removal of `String.format()`. This method
is actually used in the code (and in third-party libraries) for other
things than logging so forcing its removal can do more harm than good.

app/build.gradle

@@ -48,6 +48,14 @@ android {
             minifyEnabled true
             shrinkResources true
             proguardFiles 'proguard-rules.pro'
+
+            kotlinOptions {
+                freeCompilerArgs = [
+                    "-Xno-param-assertions",
+                    "-Xno-call-assertions",
+                    "-Xno-receiver-assertions"
+                ]
+            }
         }
     }
 

app/proguard-rules.pro

@@ -1,42 +1,36 @@
 # GENERAL OPTIONS
 
-# turn on all optimizations except those that are known to cause problems on Android
--optimizations !code/simplification/cast,!field/*,!class/merging/*
--optimizationpasses 6
 -allowaccessmodification
--dontpreverify
 
--dontusemixedcaseclassnames
--dontskipnonpubliclibraryclasses
--keepattributes *Annotation*
+# Preserve some attributes that may be required for reflection.
+-keepattributes RuntimeVisible*Annotations, AnnotationDefault
 
 # For native methods, see http://proguard.sourceforge.net/manual/examples.html#native
 -keepclasseswithmembernames class * {
     native <methods>;
 }
-# keep setters in Views so that animations can still work.
-# see http://proguard.sourceforge.net/manual/examples.html#beans
--keepclassmembers public class * extends android.view.View {
-    void set*(***);
-    *** get*();
-}
-# We want to keep methods in Activity that could be used in the XML attribute onClick
--keepclassmembers class * extends android.app.Activity {
-    public void *(android.view.View);
-}
-# For enumeration classes, see http://proguard.sourceforge.net/manual/examples.html#enumerations
--keepclassmembers enum * {
-    public static **[] values();
-    public static ** valueOf(java.lang.String);
-}
+
 -keepclassmembers class * implements android.os.Parcelable {
     public static final ** CREATOR;
 }
 
--keepclassmembers class **.R$* {
-    public static <fields>;
+# Preserve annotated Javascript interface methods.
+-keepclassmembers class * {
+    @android.webkit.JavascriptInterface <methods>;
 }
 
+# The support libraries contains references to newer platform versions.
+# Don't warn about those in case this app is linking against an older
+# platform version. We know about them, and they are safe.
+-dontnote androidx.**
+-dontwarn androidx.**
+
+# This class is deprecated, but remains for backward compatibility.
+-dontwarn android.util.FloatMath
+
+# These classes are duplicated between android.jar and core-lambda-stubs.jar.
+-dontnote java.lang.invoke.**
+
 # TUSKY SPECIFIC OPTIONS
 
 # keep members of our model classes, they are used in json de/serialization
@@ -73,9 +67,8 @@
 -keep,allowobfuscation,allowshrinking class kotlin.collections.Map
 -keep,allowobfuscation,allowshrinking class retrofit2.Call
 
-# https://r8.googlesource.com/r8/+/refs/heads/master/compatibility-faq.md#retrofit
--keepattributes Signature
--keep class kotlin.coroutines.Continuation
+# https://github.com/square/retrofit/pull/3563
+-keep,allowobfuscation,allowshrinking class kotlin.coroutines.Continuation
 
 # preserve line numbers for crash reporting
 -keepattributes SourceFile,LineNumberTable