In graphql-js resolvers expose a fourth argument called resolve info. This field contains more information about the field.
From the GraphQL docs GraphQLObjectType config parameter type definition:
// See below about resolver functions.
type GraphQLFieldResolveFn = (
source?: any,
args?: {[argName: string]: any},
context?: any,
info?: GraphQLResolveInfo
) => any
type GraphQLResolveInfo = {
fieldName: string,
fieldNodes: Array<Field>,
returnType: GraphQLOutputType,
parentType: GraphQLCompositeType,
schema: GraphQLSchema,
fragments: { [fragmentName: string]: FragmentDefinition },
rootValue: any,
operation: OperationDefinition,
variableValues: { [variableName: string]: any },
}
In the fieldNodes field you can search for your field and get the selectionSet for the particular field. From here it gets tricky since the selections can be normal field selections, fragments or inline fragments. You would have to merge all of them to know all fields that are selected on a field.