Gradle: add dependency for a specific flavour of the library

In your library you need to tell gradle to build every time every variant:

android {
    publishNonDefault true
}

Then in your application, since recently I guess, you can do this:

dependencies {
    (...)
    devCompile project(path: ':lib', configuration: 'devDebug') // or 'devRelease'
    storeCompile project(path: ':lib', configuration: 'storeRelease') // or 'storeDebug'
}

Found in the official documentation under Library Publication.

Edit:

Since version 0.14.3 (2014/11/18), you can now have Flavor-buildType-Compile directive as well:

In your build.gradle before the android {} scope add the following:

configurations {
    devDebugCompile
    devReleaseCompile
    storeDebugCompile
    storeReleaseCompile
}

Then you can declare and use different versions of your library per Flavor-BuildType:

dependencies {
    (...)
    devDebugCompile project(path: ':lib', configuration: 'devDebug')
    devReleaseCompile project(path: ':lib', configuration: 'devRelease')
    storeDebugCompile project(path: ':lib', configuration: 'storeDebug')
    storeReleaseCompile project(path: ':lib', configuration: 'storeRelease') 
}

Edit:

Dependency management between modules has changed since Android Gradle Plugin 3.0.0. It automatically tries to matches flavours between your app and the libraries/modules it depends on.

See the documentation for the whole explanation!