Interface type safety

[janheinrichmerker]

Description

graphqlgen doesn't enforce type safety for type interfaces.

Steps to reproduce

Schema:

interface Availability {
	isAvailable: Boolean!
}
type EstimatedAvailability implements Availability {
	isAvailable: Boolean!
    timestamp: Int!
}
type RemainingAvailability implements Availability {
	isAvailable: Boolean!
    remainingItems: Int!
}
type Offer {
    availability: Availability!
}

Model classes:

export interface Availability {
	isAvailable: boolean
}
export interface EstimatedAvailability {
	isAvailable: boolean
	timestamp: number
}
export interface RemainingAvailability {
	isAvailable: boolean
	remainingItems: number
}
export interface Offer {
	availability: Availability
}

Expected results

export namespace OfferResolvers {

  export type AvailabilityResolver = (
    parent: Offer,
    args: {},
    ctx: Context,
    info: GraphQLResolveInfo
  ) => Availability | Promise<Availability>;

  export interface Type {
    availability: (
      parent: Offer,
      args: {},
      ctx: Context,
      info: GraphQLResolveInfo
    ) => Availability | Promise<Availability>;
  }
}

Actual results

export namespace OfferResolvers {

  export type AvailabilityResolver = (
    parent: Offer,
    args: {},
    ctx: Context,
    info: GraphQLResolveInfo
  ) => {} | Promise<{}>;

  export interface Type {
    availability: (
      parent: Offer,
      args: {},
      ctx: Context,
      info: GraphQLResolveInfo
    ) => {} | Promise<{}>;
  }
}

Versions

• graphqlgen: 0.4.0
• OS name and version: Node 8.11.2, NPM 6.4.1, Windows 10, 64 Bit

[timsuchanek]

This is related to #149

[jasonkuhrt]

@heinrichreimer with #149 the result looks like this (slightly edited to my preference):

export namespace OfferResolvers {
  export type AvailabilityResolver = (
    parent: Offer,
    args: {},
    ctx: Context,
    info: GraphQLResolveInfo,
  ) =>
    | EstimatedAvailability
    | RemainingAvailability
    | null
    | Promise<EstimatedAvailability | RemainingAvailability | null>

  export interface Type {
    availability: AvailabilityResolver
  }

  export const defaultResolvers = {
    availability: (parent: Offer) => parent.availability,
  }
}

I also had to change your model slightly:

export interface Availability {
  isAvailable: boolean
}

export interface EstimatedAvailability extends Availability {
  timestamp: number
}

export interface RemainingAvailability extends Availability {
  remainingItems: number
}

export interface Offer {
  availability: RemainingAvailability | EstimatedAvailability
}