expose in UI all possible mapnik datasource options

[springmeyer]

We need a mapnik-reference-like json listing of all datasource options. I think it should start as a standalone json metadata file stored in TileMill - much later on we could look at moving it into mapnik-reference or into mapnik proper.

something like:

{
  'csv' : {
      'file': {
         required: true,
         doc: "the path to a csv file, required unless 'inline' option is used"
         ui: true
      },
      inline: {
        required: false,
        doc: "a raw string of data",
        ui: false
      }
      ....
  }
}

[nvkelso]

+1

[yhahn]

Great idea

[springmeyer]

starting work on this at mapnik/mapnik-reference#44 because in working with TileMill I'm constantly reminded of this deficiency, having this file will greatly help with mapnik unit tests and catching bugs, and perhaps with this in place @ansis could plan a sprint on a UI around it. Longer term I imagine that TileMill projects could share or inherit datasource settings perhaps as discussed at #1269 (to help with issues like gravitystorm/openstreetmap-carto#4), and this file could make that easier.