title: Android Studio consumerProguardFiles for the library doesn't work
body: <p>I'd like to use proguard on my library, but the file (rules) should be set inside the library. That means I don't want to set the rules w(hich belong to the library) explicitly in my app module.</p>
  
  <p>I found that there is something like <strong>consumerProguardFiles</strong> property. My settings:</p>
  
  <p><strong>library gradle:</strong></p>
  
  <pre><code>buildTypes {
      debug {
          debuggable true
          minifyEnabled false
      }
      release {
          minifyEnabled true
          consumerProguardFiles 'proguard-rules.pro'
      }
  }
  </code></pre>
  
  <p><strong>app gradle:</strong></p>
  
  <pre><code>buildTypes {
      debug {
          applicationIdSuffix ".debug"
          debuggable true
          minifyEnabled false
          signingConfig signingConfigs.debug
      }
      release {
          debuggable false
          minifyEnabled true
          signingConfig signingConfigs.release
          proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
      }
  }
  </code></pre>
  
  <p><strong>Why does configuration above doesn't work?</strong> I get errors that packages/symbols from the library cannot be found.</p>
  
  <hr>
  
  <p><strong>Edited:</strong></p>
  
  <p><em>What is important my proguard-rules.pro for the library and proguard-rules.pro for the main app module are both empty.</em></p>
  
  <p>Exemplary errors:</p>
  
  <pre><code>Error:(3, 60) error: package (my library package here) does not exist
  (...)
  Error:(16, 9) error: cannot find symbol class NavigationStructureModel
  (...)
  </code></pre>
  
  <p>More then one handrued errors. As I can see my all classes from the library are missing.</p>