title: Value interpolation with hydra composition
body: <p>I am using hydra composition with the following structure:</p>
  <pre class="lang-py prettyprint-override"><code>├── configs
      │   ├── config.yaml
      │   ├── data
      │   │   ├── dataset_01.yaml
      │   │   └── dataset_02.yaml
      │   └── model
      │       ├── bert.yaml
      │       └── gpt.yaml
  </code></pre>
  <ul>
  <li>config.yaml</li>
  </ul>
  <pre class="lang-py prettyprint-override"><code>defaults:
    - model: bert
    - data: dataset_01
  
  ...
  
  </code></pre>
  <ul>
  <li>data/dataset_01.yaml</li>
  </ul>
  <pre class="lang-py prettyprint-override"><code># @package _group_
  
  name: &quot;dataset_01&quot;
  
  train:
    path: &quot;../resources/datasets/dataset_01/train.jsonl&quot;
    num_samples: 1257391
  
  test:
    path: &quot;../resources/datasets/dataset_01/test.jsonl&quot;
    num_samples: 71892
  
  val:
    path: &quot;../resources/datasets/dataset_01/val.jsonl&quot;
    num_samples: 73805
  
  </code></pre>
  <ul>
  <li>model/bert.yaml</li>
  </ul>
  <pre class="lang-py prettyprint-override"><code># @package _group_
  
  name: &quot;bert&quot;
  
  encoder: &quot;source.encoder.BertEncoder.BertEncoder&quot;
  
  encoder_hparams:
    architecture: &quot;bert-base-uncased&quot;
  
  lr: 1e-7
  
  tokenizer:
    architecture: &quot;bert-base-uncased&quot;
  
  predictions:
    path: &quot;../resources/predictions/bert_predictions.pt&quot;
  </code></pre>
  <ul>
  <li>entry point</li>
  </ul>
  <pre class="lang-py prettyprint-override"><code>@hydra.main(config_path=&quot;configs/&quot;, config_name=&quot;config.yaml&quot;)
  def perform_tasks(hparams):
  
      model = MyModel(hparams.model)
  
  if __name__ == '__main__':
      perform_tasks()
  </code></pre>
  <p>In the context of <code>hparams.model</code>, there is no way for OmegaConf to interpolate the key <code>data.name</code> since it is not in scope.
  So, it would be great if there was an approach to causes the interpolation at the beginning of the application.</p>