Combine Multiple Filters

[JeremyCaney]

Currently, DocFX allows custom filters to be defined for metadata imports using the filter configuration property:

{
  "metadata": [
    {
      "src": [ … ],
      "filter": "filterConfig.yml"
    }
  ]
}

This only allows one filter to be applied, however. That means that if you have multiple metadata rules defined, and each applies a different filter, any shared rules must be duplicated in each of the filters.

Options

There are a few approaches that might be pursued to resolve this. While any one of these would address the scenario I've laid out above, these each offer tradeoffs, and aren't actually mutually exclusive to one another; were it a priority, each of these options could be supported, and remain compatible with one another. That said, I suspect this is already an edge case, so prioritizing the simplest approach makes the most sense:

1. Allow the filter property to accept an array of filters, similar to other properties (e.g., src).
2. Allow a custom filter's yml definition to inherit from or include another filter.
3. Allow a custom global filter to be defined, which all metadata rules will be based off of.

All of these would require for filter rules to be merged, though that's already supported with the out-of-the-box default filter configuration.