Long term this could allow Galaxy to support - multiple tooling formats (Galaxy-like YAML, CWL http://bit.ly/cwltooldesc, etc...). But I think it is also important from a purely design perspective - this is a core logic class integrating different components - they should not also be doing XML parsing.
To verify the interface for parsing tools is expressive enough to allow multiple useful implementations, I built a test YAML tool description that implements many of the same features as Galaxy but smooths out rough edges (uses exit codes for job failure by default for instance). Loading these tools is disabled by default and it is not documented how to enable them because they are not intended to be part of Galaxy's public API.
This reduces code duplication related dataset_collectors now and abstracts out important functionality I reuse further to collect dataset collections downstream.
Was originally added in 28d43f4 as DatasetParamContext and backed out of right away. I have reworked it so that it no longer breaks implicit conversion, the relevant classes and methods have less generic names, and it has a healthy set of test cases.
In addition to basic tests on matching datasets to parameters, selections, and implicit conversions - these tests include testing of dataset security inconjuction with data_destination tools as well as filtering data parameters on other data parameters.
Dannon Baker