Federation support checklist

[eddeee888]

• @key
  • ref should not be mapper [resolvers][federation] Fix mapper being incorrectly used as the base type for reference #10216
  • __resolveReference should return mapper if available
  • Defining advanced @keys
    • composite @key work e.g. @key(fields: "id anotherId")
    • nested @key work e.g. @key(fields: "id organization { id }")
    • multiple @key work e.g. @key(fields: "id") @key(fields: "id2")
• @interfaceObject
  • No types required
• @extends
  • No types required
• @shareable
  • No types required: this is used during composition check to say whether a field can be resolved by multiple subgraphs or used as another Graph's @key (which is implicitly shareable)
• @inaccessible
  • If an enum member is marked with inaccessible, omit it from types, otherwise there could be runtime errors
• @override
  • No types required: this is used to migrate field resolving from one subgraph to another
• @external
  • If a field is marked with @external, do not generate resolver types.
  • If a type is marked with @external , generate the base type but not resolver types
  • Server Preset must not generate resolvers i.e. use resolver types instead of type interface to compare fields against mappers
• @provides
  • When @provides is used on an @external field, the field resolver type is generated
  • @provides works with nested path
• @requires
  • Fields marked with @requires must use the normal mappers, instead of the GraphQLRecursivePick with the @key and @requires fields.
  • When there's a field marked with @requires, the __resolveReference 's ref must have a union of possible combination e.g.

type User @key(fields: "id") {
  id: ID!
  title: PersonTitle! @external
  firstName: String! @external
  lastName: String! @external
  birthYear: Int! @external

  fullName: String! @requires(fields: "firstName lastName")
  fullNameWithTitle: String! @requires(fields: "firstName lastName title")
  age: Int! @requires(fields: "birthyear")
}

Then, the type of reference is something like:

ReferenceResolver<
    Maybe<ResolversTypes["User"]>,
    { __typename: "User" } 
   & GraphQLRecursivePick<ParentType, { id: true }> // <-- from @key, must always be here
   & GraphQLRecursivePick<ParentType, { firstName?: true; lastName?: true }> <-- from @requires
   & GraphQLRecursivePick<ParentType, { firstName?: true; lastName?: true, title?: true }> <-- from @requires
   & GraphQLRecursivePick<ParentType, { birthyear?: true }> <-- from @requires
   , ContextType
  >

Note: the type for @requires needs a re-think because if fullName is in the selection set, firstName and lastName must exist in the ref together. The example above is saying there could be a scenario where firstName is there but lastName is not. We need something like AnyCombinationOf<ArrayOfRequiresOptions>

• @tag
  • No types needed
• @composeDirective
  • No types needed

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Enterprise directives

• @authenticated
• @requiresScopes
• @policy
• @context
• @fromContext
• @cost
• @listSize