Unable to build a release build in Kotlin

Question

After having converted my Android project to Kotlin I am unable to build a release build, the error appears to be related to Proguard.

I see 155 warnings like

Warning:com.example.app.activity.MainActivity$1: can't find referenced field 'android.view.View decorView' in program class com.example.app.activity.MainActivity
Warning:com.example.app.activity.MainActivity$2: can't find referenced field 'android.os.Handler handler' in program class com.example.app.activity.MainActivity

and the build fails with

Error:Execution failed for task ':MyApp:transformClassesAndResourcesWithProguardForFreeRelease'.
> Job failed, see logs for details

If I change these directives in build.grade from true to false the build succeeds.

minifyEnabled true
shrinkResources true

Any suggestions on what the issue might be?

Edit:

The proguard files are below:

proguard-android.txt

# This is a configuration file for ProGuard.
# http://proguard.sourceforge.net/index.html#manual/usage.html

-dontusemixedcaseclassnames
-dontskipnonpubliclibraryclasses
-verbose

# Optimization is turned off by default. Dex does not like code run
# through the ProGuard optimize and preverify steps (and performs some
# of these optimizations on its own).
-dontoptimize
-dontpreverify

# If you want to enable optimization, you should include the
# following:
# -optimizations !code/simplification/arithmetic,!code/simplification/cast,!field/*,!class/merging/*
# -optimizationpasses 5
# -allowaccessmodification
#
# Note that you cannot just include these flags in your own
# configuration file; if you are including this file, optimization
# will be turned off. You'll need to either edit this file, or
# duplicate the contents of this file and remove the include of this
# file from your project's proguard.config path property.

-keepattributes *Annotation*
-keep public class * extends android.app.Activity
-keep public class * extends android.app.Application
-keep public class * extends android.app.Service
-keep public class * extends android.content.BroadcastReceiver
-keep public class * extends android.content.ContentProvider
-keep public class * extends android.app.backup.BackupAgent
-keep public class * extends android.preference.Preference
-keep public class * extends android.support.v4.app.Fragment
-keep public class * extends android.app.Fragment
-keep public class com.android.vending.licensing.ILicensingService


# For native methods, see http://proguard.sourceforge.net/manual/examples.html#native
-keepclasseswithmembernames class * {
    native <methods>;
}

-keep public class * extends android.view.View {
    public <init>(android.content.Context);
    public <init>(android.content.Context, android.util.AttributeSet);
    public <init>(android.content.Context, android.util.AttributeSet, int);
    public void set*(...);
}

-keepclasseswithmembers class * {
    public <init>(android.content.Context, android.util.AttributeSet);
}

-keepclasseswithmembers class * {
    public <init>(android.content.Context, android.util.AttributeSet, int);
}

-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);
}

-keep class * implements android.os.Parcelable {
  public static final android.os.Parcelable$Creator *;
}

-keepclassmembers class **.R$* {
    public static <fields>;
}

# The support library 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.
-dontwarn android.support.**
-dontwarn io.codetail.animation.**

proguard-rules.txt

# Add project specific ProGuard rules here.
# By default, the flags in this file are appended to flags specified
# in /home/francesc/droids/android-sdk-linux/tools/proguard/proguard-android.txt
# You can edit the include path and order by changing the ProGuard
# include property in project.properties.
#
# For more details, see
#   http://developer.android.com/guide/developing/tools/proguard.html

# Add any project specific keep options here:

# If your project uses WebView with JS, uncomment the following
# and specify the fully qualified class name to the JavaScript interface
# class:
#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
#   public *;
#}

-keep class com.nineoldandroids.** { *; }
-dontwarn io.codetail.animation.**

The signing config is defined as shown below

signingConfigs {
    myConfig {
        Properties keyProps = new Properties()
        keyProps.load(new FileInputStream(file('../release.properties')))
        storeFile file(keyProps["store"])
        keyAlias keyProps["alias"]
        storePassword keyProps["storePass"]
        keyPassword keyProps["keyPass"]
    }
}

buildTypes {
    release {
        proguardFiles 'proguard-android.txt', 'proguard-rules.txt'
        minifyEnabled true
        shrinkResources true
        signingConfig signingConfigs.myConfig
    }
}

Answer 1

Try to add @Keep annotation to the class in question (e.g. MainActivity) and see if it helps. If it does, it means that minify is renaming some resource, that shouldn't be renamed because some other resource expects it by it's original name.