android: enable proguard (#399)

Signed-off-by: kari-ts <kari@tailscale.com>

android/build.gradle

@@ -69,6 +69,15 @@ android {
             buildConfigField "String", "GITHUB_PASSWORD", "\"" + getLocalProperty("githubPassword")+"\""
             buildConfigField "String", "GITHUB_2FA_SECRET", "\"" + getLocalProperty("github2FASecret")+"\""
         }
+        release {
+            minifyEnabled true
+
+            shrinkResources true
+
+            proguardFiles getDefaultProguardFile(
+                    'proguard-android-optimize.txt'),
+                    'proguard-rules.pro'
+        }
     }
 
     testBuildType "applicationTest"

android/proguard-rules.pro

@@ -0,0 +1,21 @@
+# Keep all classes with native methods
+-keepclasseswithmembernames class * {
+    native <methods>;
+}
+
+# Keep specific classes from Tink library
+-keep class com.google.crypto.tink.** { *; }
+
+# Ignore warnings about missing Error Prone annotations
+-dontwarn com.google.errorprone.annotations.**
+
+# Keep Error Prone annotations if referenced
+-keep class com.google.errorprone.annotations.** { *; }
+
+# Keep Google HTTP Client classes
+-keep class com.google.api.client.http.** { *; }
+-dontwarn com.google.api.client.http.**
+
+# Keep Joda-Time classes
+-keep class org.joda.time.** { *; }
+-dontwarn org.joda.time.**