Is it possible to specify a type for scalar types during type generation?

[ysfaran]

Issue

So when you use custom or third party scalar types as shown here:

const DateScalar = scalarType({
  name: 'Date',
  asNexusMethod: 'date',
  description: 'Date custom scalar type',
  parseValue(value) {
    return new Date(value)
  },
  serialize(value) {
    return value.getTime()
  },
  parseLiteral(ast) {
    if (ast.kind === Kind.INT) {
      return new Date(ast.value)
    }
    return null
  },
})

nexus will generate an interface for the scalars like so:

export interface NexusGenScalars {
  String: string
  Int: number
  Float: number
  Boolean: boolean
  ID: string
  Address: any
  Date: any
  JSONObject: any
}

This is really unfortunate because having the types set to any breaks type safety.

Question

Is there a way to specify types for custom/third party scalar types?

Taking the example above I would have liked to have following interface generated:

export interface NexusGenScalars {
  // ...
  Address: string
  Date: Date
  JSONObject: Record<string, any>
}

[eysterbrian]

After looking into this same issue myself, it appears that asNexusMethod() takes a 3rd argument: sourceType?: SourceTypingDef.

Here's the full function declaration:
export declare function asNexusMethod<T extends GraphQLScalarType>(scalar: T, methodName: string, sourceType?: SourceTypingDef): T;

Digging into the types of SourceTypingDef, you can specify the generated TS type for a scalar by providing either: the type as a string; or an object that contains the module and export for the type (the TypingImport interface).

I think this code will generate what you're looking for (using resolvers from graphql-scalars):

export const GQLDate = asNexusMethod(GraphQLDateTime, 'dateTime', 'Date');
export const GQJson = asNexusMethod(GraphQLJSONObject, 'json', 'Record<string, any>');

In my case, I was trying to create a custom URL scalar with the built-in node 'URL' class as its TS type. Here's how I got that to work using a TypingImport object for the 3rd parameter:

export const GQLUrl = asNexusMethod(GraphQLURL, 'url', {  
  module: 'url',
  export: 'URL',
});