feat: allow functional directives via schemaTransforms

[AdrienLemaire]

The graphql-tools documentation suggests to write functional directives instead of class-based ones.

This can be done with neo4j-graphql-js by allowing the schemaTransforms key to makeAugmentedSchema:

const schema = makeAugmentedSchema({
  typeDefs,
  schemaTransforms: [canUpdateRoleTransformer],
});

Example of functional directive I could get working with my fork of neo4j-graphql-js

const canUpdateRoleTransformer = (schema: GraphQLSchema): GraphQLSchema =>
  mapSchema(schema, {
    [MapperKind.OBJECT_FIELD]: (fieldConfig) => {
      let directives: DirectiveUseMap;
      try {
        directives = getDirectives(schema, fieldConfig);
      } catch {
        // GraphQLError [Object]: Argument "direction" has invalid value "BOTH".
        // Not sure why but I'm getting this error when getdirectives reads @relation
        return fieldConfig;
      }

      if (directives.canUpdateRole) {
        const { resolve = defaultFieldResolver } = fieldConfig;
        return {
          ...fieldConfig,
          resolve: async (source, args, context, info) => {
            const decoded = verifyAndDecodeToken({ context });

            const isAuthorized = await context.models.User.canUpdateRoleFor(
              args
            );
            if (isAuthorized) {
              return resolve(source, args, { ...context, user: decoded }, info);
            }

            throw new AuthorizationError({
              message: "unauthorized_resource",
            });
          },
        };
      }
      return fieldConfig;
    },
  });

export default canUpdateRoleTransformer;

[michaeldgraham]

Thank you for catching this!