New typegen auto config configuration

The follow proposal comes from an unplanned brainstorm session with @Weakky.

Example:

const schema = makeSchema({
  sourceTypes: {
    modules: [
      { style: 'as', name: 'Prisma', from: '@prisma/client' },
      { style: 'as', name: 'Foo', from: '@foo/bar' },
    ],
    mappings: {
      User: 'Prisma.User',
      Foo: { raw: 'ReturnType<typeof Prisma.User["abc"]>' },
    },
    mappingPatterns: [
      // lowest level
      (gqlTypeName, fullyQualifiedTSTypeName) => {
        if (!gqlTypeName.match(/.../)) {
          if (fullyQualifiedTSTypeName.startsWith('Foo')) {
            return `${gqlTypeName}Entity` as const
          }
          return undefined
        }

        return `${gqlTypeName}Entity` as const
      },
      // helper functions, we can bundle some, users can provide others
      // exactMatch(),
      // ExcludeTypes(/^Foo/)((gqlTypeName, fqtn) => ...),
      // pattern('${GraphQLTypeName}Entity'),
      // regexPattern((graphqlTypeName) => `${graphqlTypeName}Entity`),
    ],
  },
})

Types

// inject arbitrary TS types/type-logic into typegen TS file
type RawMapping = {
  raw: string
}

type NexusGenOutputTypeNames = '...'

// The types extracted from specified modules
type NexusGenTypePoolNames = '...'

// no way to express named imports, intentional
type ImportSpec = 
  | { from: string; name: string; style: 'as' | 'default'}
  | { from: RegExp; import: (path: string) => { name: string, style: 'as' | 'default' } } 

type MappingPattern = (
  graphQLSchemaTypeName: NexusGenOutputTypeNames,
  fullyQualifiedTypeScriptTypeName: NexusGenTypePoolNames
) => undefined | null | NexusGenTypePoolNames | RawMapping

type SourceTypesConfig = {
  modules: ImportSpec[]
  mappings: Record<NexusGenOutputTypeNames, NexusGenTypePoolNames | RawMapping>
  mappingPatterns: MappingPattern[]
}

Points:

Separate type mapping from module locations
Simplify to just direct mappings and patterns
Encourage pattern helper functions
complete type safety based on typegen based on the results found by looking at the specified module locations
great runtime and static feedback, no silent errors
great discoverability thanks to autocomplete
escape hatches maintained with raw mappings
find modules by regex patterns!

graphql-nexus / nexus

New typegen auto config configuration #727