Use ProGuard to strip unused code in release builds (#2753)

k9mail/build.gradle

@@ -77,6 +77,9 @@ android {
                 signingConfig signingConfigs.release
             }
 
+            minifyEnabled true
+            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
+
             buildConfigField "boolean", "DEVELOPER_MODE", "false"
         }
 

k9mail/proguard-rules.pro

@@ -0,0 +1,23 @@
+# Add project specific ProGuard rules here.
+
+-dontobfuscate
+
+# Preserve the line number information for debugging stack traces.
+-keepattributes SourceFile,LineNumberTable
+
+# Library specific rules
+-dontnote android.net.http.*
+-dontnote org.apache.commons.codec.**
+-dontnote org.apache.http.**
+-dontnote com.squareup.moshi.**
+-dontnote com.github.amlcurran.showcaseview.**
+-dontnote de.cketti.safecontentresolver.**
+-dontnote com.tokenautocomplete.**
+
+-dontwarn okio.**
+-dontwarn com.squareup.moshi.**
+
+# Project specific rules
+-dontnote com.fsck.k9.PRNGFixes
+-dontnote com.fsck.k9.ui.messageview.**
+-dontnote com.fsck.k9.view.**