Combine fields and computedFields

[seancdavis]

Today we have fields and computedFields. The definitions in computedFields expects a function to which Contentlayer passes the processed document.

I'd rather be able to define all my fields in one place and allow the options of that field definition (presence of resolve) to determine whether or not it should be computed. Thus, I could have a doc type def like this:

const Page = defineDocumentType(() => ({
  // ...
  fields: {
    title: { type: 'string', required: true },
    url_path: {
      type: 'string',
      resolve: (doc) => doc._raw.flattenedPath.replace(/pages\/?/, ''),
    },
  },
}))

To do this and still support current use cases, it'd be beneficial to not just pass the processed doc object, but also input data. (See #76 for an example use case.) IOW the shape of the doc passed to the resolve function might include the following properties:

• _raw would still be there as it is today
• frontmatter would contain the raw frontmatter content
• body (configurable) would contain the processed body

[schickling]

Related to #76

[airtonix]

A few things the current format has going for it are:

• simplicity: the type definitions for fields and computedFields is easier to manage as separate signatures, combining them smells like the poision of D.R.Y zealotry.
• it's obvious what they do.