Patch applies cleanly, tests pass, although I notice several @ignore in there. Docs look good in my preliminary perusing. I've only started looking at things, and have a lot of reading to catch up on, so these first comments, please take with a grain of salt, as the English saying goes...
I'd suggest,that instead of relying on MySQL in TestJdbcDataSource, we instead use and embedded Derby or some sort of JDBC mock. I suggest Derby mainly b/c it's already ASF and I don't want to bother looking up licenses for HSQL or any of the others that might work.
Also, I notice several interfaces that have a number of methods on them. Have you thought about abstract base classes instead? I know, there is a whole big debate over it, and people will argue that if you get the interface exactly correct, you should use interfaces. Nice in theory, but Lucene/Solr experience suggests that rarely happens. Of course, I think the correct way is to actually do both, as one can easily decorate an abstract base class with more interfaces as needed. Just food for thought, b/c what's going to quickly happen after release is someone is going to need a new method on the DataSource or something and then we are going to be stuck doing all kinds of workarounds due to back compatibility reasons. The alternative is to clearly mark all Interfaces as being experimental at this point and clearly note that we expect them to change. We may even want to consider both! The other point, though, is contrib packages need not be held to the same standard as core when it comes to back compat.
What relation does the Context have to the HttpDataSource? In other words, the DataSource init method takes a Context, meaning the HttpDataSource needs a Context, yet in my first glance at the Context, it seems to be DB related.
What if I wanted to slurp from a table on the fly? That is, I want to send in a select statement in my request and I let the columns line up where they may Field wise (i.e. via dynamic fields or I rely on something like select id, colA as fieldA, colB as fieldB from MyTable; )
Is that possible?
Interactive mode has a bit of a chicken and the egg problem when it comes to JDBC, right, in that the Driver needs to be present in Solr/lib right? So, one can currently only interactively configure a JDBC DataSource if the driver is already in lib and loaded by the ClassLoader. If you haven't already, it might actually be useful to show what drivers are present by using the DriverManager.
In the JDBCDataSource, not sure I follow the connection stuff. Can you explain a bit? Also, what if I wanted to plug in my own Connection Pooling library, as I may already have one setup for other things (if using Solr embedded)?