Gradle : how to use BuildConfig in an android-library with a flag that gets set in an app

My (gradle 1.10 and gradle plugin 0.8)-based android project consists of a big android-library that is a dependency for 3 different android-apps

In my library, I would love to be able to use a structure like this

if (BuildConfig.SOME_FLAG) {
    callToBigLibraries()
}

as proguard would be able to reduce the size of the produced apk, based on the final value of SOME_FLAG

But I can't figure how to do it with gradle as :

* the BuildConfig produced by the library doesn't have the same package name than the app
* I have to import the BuildConfig with the library package in the library
* The apk of an apps includes the BuildConfig with the package of the app but not the one with the package of the library.

I tried without success to play with BuildTypes and stuff like

release {
    // packageNameSuffix "library"
    buildConfigField "boolean", "SOME_FLAG", "true"
}
debug {
    //packageNameSuffix "library"
    buildConfigField "boolean", "SOME_FLAG", "true"
}

What is the right way to builds a shared BuildConfig for my library and my apps whose flags will be overridden at build in the apps?

As a workaround, you can use this method, which uses reflection to get the field value from the app (not the library):

/**
 * Gets a field from the project's BuildConfig. This is useful when, for example, flavors
 * are used at the project level to set custom fields.
 * @param context       Used to find the correct file
 * @param fieldName     The name of the field-to-access
 * @return              The value of the field, or {@code null} if the field is not found.
 */
public static Object getBuildConfigValue(Context context, String fieldName) {
    try {
        Class<?> clazz = Class.forName(context.getPackageName() + ".BuildConfig");
        Field field = clazz.getField(fieldName);
        return field.get(null);
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    }
    return null;
}

To get the DEBUG field, for example, just call this from your Activity:

boolean debug = (Boolean) getBuildConfigValue(this, "DEBUG");

I have also shared this solution on the AOSP Issue Tracker.

Update: With newer versions of the Android Gradle plugin publishNonDefault is deprecated and has no effect anymore. All variants are now published.

The following solution/workaround works for me. It was posted by some guy in the google issue tracker:

Try setting publishNonDefault to true in the library project:

android {
    ...
    publishNonDefault true
    ...
}

And add the following dependencies to the app project that is using the library:

dependencies {
    releaseCompile project(path: ':library', configuration: 'release')
    debugCompile project(path: ':library', configuration: 'debug')
}

This way, the project that uses the library includes the correct build type of the library.