Support for directives

[louy]

Hi there,

Awesome tool. We're strongly considering using it. Quick question on directives because I can't find anything in the docs:

How do you declare directives? How do you annotate different fields/types with directives?

[captbaritone]

Grats does not currently support adding or defining arbitrary schema directives, but it seems like a reasonable thing to support. Could you tell me more about the specific directives you you use that you'd like to support? Would help inform how they should be supported.

[louy]

For anyone interested, I have just hacked a solution for now. This also serves as an example of directives we have:

import { MapperKind, mapSchema } from '@graphql-tools/utils';
import { GraphQLSchema } from 'graphql';
import type { Int } from 'grats';

type Directive = {
  name: 'complexity' | 'sensitive';
  args: Record<string, unknown>;
};

/**
 * Directive controlling query cost analytics
 */
export function complexity(
  /** The complexity value for the field - works as described in (graphql-query-complexity)[https://github.com/slicknode/graphql-query-complexity/blob/master/src/estimators/directive/README.md]
   *
   */
  value: Int,

  /** Information how field arguments influence cost of returned list - works as described in (graphql-query-complexity)[https://github.com/slicknode/graphql-query-complexity/blob/master/src/estimators/directive/README.md]
   *
   */
  multipliers?: string[],

  /** Cost of field assign to directive doesn't depend on multiplier but cost of nested fields yes
   *
   */
  multiplyOnlyNestedFields?: boolean,

  /** In situation where we cannot define multiplier depending on arguments we use defaultValue to multiple
   *
   */
  defaultMultiplier?: Int,
): Directive {
  return {
    name: 'complexity',
    args: {
      value,
      multipliers,
      multiplyOnlyNestedFields,
      defaultMultiplier,
    },
  };
}

/** Marks a field as sensitive so it gets redacted in logs */
export function sensitive(
  /**An optional reason why the field is marked as sensitive*/
  reason?: string,
): Directive {
  return {
    name: 'sensitive',
    args: { reason },
  };
}

const directivesList: (
  | {
      directive: Directive;
      kind: 'FIELD';
      parent: string;
      name: string;
    }
  | {
      directive: Directive;
      kind: 'ARGUMENT';
      parent: string;
      field: string;
      argument: string;
    }
  | {
      directive: Directive;
      kind: 'TYPE';
      name: string;
    }
)[] = [];

export function addDirective(
  directive: Directive,
  kind: 'FIELD',
  parent: string,
  name: string,
): void;
export function addDirective(
  directive: Directive,
  kind: 'ARGUMENT',
  parent: string,
  field: string,
  argument: string,
): void;
export function addDirective(
  directive: Directive,
  kind: 'TYPE',
  name: string,
): void;
export function addDirective(
  directive: Directive,
  kind: 'TYPE' | 'FIELD' | 'ARGUMENT',
  arg1: string,
  arg2?: string,
  arg3?: string,
) {
  switch (kind) {
    case 'FIELD':
      directivesList.push({
        directive,
        kind,
        parent: arg1!,
        name: arg2!,
      });
      break;
    case 'ARGUMENT':
      directivesList.push({
        directive,
        kind,
        parent: arg1!,
        field: arg2!,
        argument: arg3!,
      });
      break;
    case 'TYPE':
      directivesList.push({
        directive,
        kind,
        name: arg1!,
      });
      break;
  }
}

export function applyDirectives(schema: GraphQLSchema) {
  const cloned = directivesList.slice();
  const mapped = mapSchema(schema, {
    [MapperKind.TYPE]: (type) => {
      const applicable = cloned.filter(
        (directive) =>
          directive.kind === 'TYPE' && directive.name === type.name,
      );

      if (applicable.length === 0) {
        return type;
      }

      type.extensions = type.extensions ?? {};

      const extensions: any = type.extensions;
      extensions.directives = extensions.directives ?? {};

      for (const item of applicable) {
        extensions.directives[item.directive.name] = item.directive.args;
        cloned.splice(cloned.indexOf(item), 1);
      }
    },

    // FIELD
    [MapperKind.FIELD](fieldConfig, fieldName, typeName) {
      const applicable = cloned.filter(
        (directive) =>
          (directive.kind === 'FIELD' &&
            directive.parent === typeName &&
            directive.name === fieldName) ||
          (directive.kind === 'ARGUMENT' &&
            directive.parent === typeName &&
            directive.field === fieldName),
      );

      if (applicable.length === 0) {
        return fieldConfig;
      }

      for (const item of applicable) {
        if (item.kind === 'FIELD') {
          fieldConfig.extensions = fieldConfig.extensions ?? {};
          const extensions: any = fieldConfig.extensions;
          extensions.directives = extensions.directives ?? {};

          extensions.directives[item.directive.name] = item.directive.args;
          cloned.splice(cloned.indexOf(item), 1);
        } else if (item.kind === 'ARGUMENT' && 'args' in fieldConfig) {
          fieldConfig.args = fieldConfig.args ?? {};
          const arg = fieldConfig.args[item.argument];
          if (arg) {
            arg.extensions = arg.extensions ?? {};
            const extensions: any = arg.extensions;
            extensions.directives = extensions.directives ?? {};

            extensions.directives[item.directive.name] = item.directive.args;
            cloned.splice(cloned.indexOf(item), 1);
          }
        }
      }
    },
  });
  if (cloned.length)
    throw new Error(
      `Found unresolved directives\n${JSON.stringify(cloned, null, 2)}`,
    );
  return mapped;
}

Usage:

addDirective(complexity(50), 'FIELD', 'Mutation', 'createFcmToken');
addDirective(sensitive(), 'ARGUMENT', 'Mutation', 'createFcmToken', 'token');
/**
 * Register Firebase Cloud Messaging token
 * @gqlMutationField
 */
export async function createFcmToken(
  /** @sensitive */
  token: string,
  { fetchFreshaApi }: Context,
): Promise<FcmToken | null> {
  // ...
}

And later:

applyDirectives(getSchema())

[louy]

Basically what I'd like to see is 2 things:

1. Ability to declare directives, potentially from functions, similar to the above two exmaples I have:

/**
 * Directive controlling query cost analytics
 * @gqlDirective on FIELD_DEFINITION
 */
export function complexity(
  /** The complexity value for the field - works as described in (graphql-query-complexity)[https://github.com/slicknode/graphql-query-complexity/blob/master/src/estimators/directive/README.md]
   *
   */
  value: Int,

  /** Information how field arguments influence cost of returned list - works as described in (graphql-query-complexity)[https://github.com/slicknode/graphql-query-complexity/blob/master/src/estimators/directive/README.md]
   *
   */
  multipliers?: string[],

  /** Cost of field assign to directive doesn't depend on multiplier but cost of nested fields yes
   *
   */
  multiplyOnlyNestedFields?: boolean,

  /** In situation where we cannot define multiplier depending on arguments we use defaultValue to multiple
   *
   */
  defaultMultiplier?: Int,
): Directive {}

Generates

  "Directive controlling query cost analytics"
  directive @complexity(
    "The complexity value for the field - works as described in (graphql-query-complexity)[https://github.com/slicknode/graphql-query-complexity/blob/master/src/estimators/directive/README.md]"
    value: Int!

    "Information how field arguments influence cost of returned list - works as described in (graphql-query-complexity)[https://github.com/slicknode/graphql-query-complexity/blob/master/src/estimators/directive/README.md]"
    multipliers: [String!]

    "Cost of field assign to directive doesn't depend on multiplier but cost of nested fields yes"
    multiplyOnlyNestedFields: Boolean

    "In situation where we cannot define multiplier depending on arguments we use defaultValue to multiple"
    defaultMultiplier: Int
  ) on FIELD_DEFINITION

2. Abilty to apply directives to the various things they apply to: fields, arguments, types, enums, etc
   This one is a lot tricker because grats doesn't use decorators. My hack was to introduce a function you have to call, but it is not type-safe and I prefer a safer solution (maybe you wrap resolver functions in directive apply)

[louy]

Directives don't really have logic like resolvers, so maybe a function doesn't make sense. Usually directives are used either to apply schema transformations (using mapSchema) or to be read later in resolvers/middleware (like the sensitive directive above, used to mask values in the logging middleware)

[captbaritone]

Thanks for the examples, helps clarify!

I think a reasonable starting place would be:

Define directives

You can define a directive on a type alias of an object literal type describing the directive's arguments:

/**
 * Directive controlling query cost analytics
 * @gqlDirective complexity on FIELD_DEFINITION
 */
type Complexity = {
  /** The complexity value for the field - works as described in (graphql-query-complexity)[https://github.com/slicknode/graphql-query-complexity/blob/master/src/estimators/directive/README.md]
   *
   */
  value: Int,

  /** Information how field arguments influence cost of returned list - works as described in (graphql-query-complexity)[https://github.com/slicknode/graphql-query-complexity/blob/master/src/estimators/directive/README.md]
   *
   */
  multipliers?: string[],

  /** Cost of field assign to directive doesn't depend on multiplier but cost of nested fields yes
   *
   */
  multiplyOnlyNestedFields?: boolean,

  /** In situation where we cannot define multiplier depending on arguments we use defaultValue to multiple
   *
   */
  defaultMultiplier?: Int,
};

The @gqlDirective could be followed by either ON <...directiveLocations> in which case the type alias's name would be the directive name, or <directiveName> ON <...directiveLocations> to support aliasing the type name. Aliasing will probably be common since directives generally use snakeCase but types generally use PascalCase.

Using directives

How do you imagine the syntax for passing arguments to directives would look?

I think ideally it could be:

/**
 * @gqlField
 * @someDirective(someArg: "Hello")
 */
export class User {
  // ...
}

But we'll need to see if TypeScript will parse @someDirective(someArg: "Hello") as a docblock tag, or if we'll end up needing to do our own docblock parsing.

One thing that will be tricky is knowing which docblock tags should be interpreted as directives and which are unrelated to Grats. Elsewhere in Grats we handle this by parsing everything as if it belongs to Grats, and then in a later phase (when we know which names exist) we discard any which we learn are not related to Grats.

[louy]

I like this a lot. Yes.

The other problem with parsing however is multiline directive args

I was thinking an alternative might be

/**
 * @gqlField
 * @someDirective.shortArg String
 * @someDirective.longArg A very long
 * multi line string
 * @someDirective.booleanArg true
 * @someDirective.enumArg ENUM_VAL
 */
export class User {
  // ...
}

But then repeatable args become unclear, for that maybe you allow using only the directive name to count as the start of the invocation:

/**
 * @gqlField
 * @someDirective
 * @someDirective.shortArg String1
 * @someDirective
 * @someDirective.shortArg String2
 */
export class User {
  // ...
}

[felamaslen]

If we can agree on an approach here then I wouldn't mind contributing with an implementation.

[leo-fresha]

I think ideally it could be:

/**
 * @gqlField
 * @someDirective(someArg: "Hello")
 */
export class User {
  // ...
}

But we'll need to see if TypeScript will parse @someDirective(someArg: "Hello") as a docblock tag, or if we'll end up needing to do our own docblock parsing.

One thing that will be tricky is knowing which docblock tags should be interpreted as directives and which are unrelated to Grats. Elsewhere in Grats we handle this by parsing everything as if it belongs to Grats, and then in a later phase (when we know which names exist) we discard any which we learn are not related to Grats.

Why not @gqlDecorate <directiveName> <directiveArg>...

/**
 * @gqlType
 * @gqlDecorate cacheControl scope:PRIVATE maxAge:100
 */
type Wallet = {
  /**
   * @gqlField
   * @gqlDecorate complexity value:50
   */
  balance: Int,

  /** @gqlField */
  paymentMethods(
    /**
     * @gqlArg
     * @gqlDecorate deprecated
     */
    includeExpired: boolean | null
  ): [PaymentMethod]
}

It keeps with using @gql-prefixed doc tags. @gqlDirective to define a directive, and @gqlDecorate to decorate a target with an existing directive.
I'm not sure of the exact JSDoc syntax supported by Typescript, but there's probably a way to make this work, using curly braces or other JSDoc syntax like:

/** @gqlDecorate `complexity(value: 20, motivation: "This arg requires extra backend queries")` */

Might be worth taking a look at what TSDoc supports.

[captbaritone]

Thanks everyone for the feedback/ideas!

I looked into it a bit more and learned a few things:

1. TypeScript will let me parse @someDirective(someArg: "foo") in a docblock as a docblock tag.
2. Parsing such directives out of a docblock (by passing the text to the GraphQL-js parser and using special methods on the parser) is possible, but reporting parse errors as granular locations is not really viable due the case where the directive spans multiple lines but those lines are prefixed with * from the docblock. TS will strip those for us, so we can parse it fine, just not reliably point back to the correct source location
3. If a directive does not have arguments, it becomes indistinguishable from a docblock tag. Since we don't know all valid docblocks at extraction time, this means we would need to retain all dobblock tags as possible directives and strip them later when we are full program aware.

I think this points to something like what @leo-fresha is describing, where there's a tag that denotes "directive here" and the tag value is the directive.

That said, I'm not crazy about introducing special syntax here which deviates from both GraphQL and typescript: directives without an @, required quotes, a space after directive name...

I'm also not crazy about @gqlDecorate as a name since it does not map to any well defined name/concept in GraphQL.

Maybe @gqlDirective followed by plain old SDL directives? I'll need to check if TS treats this as two tags or one.

/**
 * @gqlType
 * @gqlDirective @cacheControl(scope:PRIVATE maxAge:100)
 */
type Wallet = {
  /**
   * @gqlField
   * @gqlDirective @complexity(value:50)
   */
  balance: Int,

That still leaves open: How do we define directives if @gqlDirective is used for adding directives...

As for @deprecated. I'd like to keep that using the existing @deprecated docblock tag since that is already a concept in TypeScript (it will render the function/method/etc as struck through).

[leo-fresha]

Personally I would keep @gqlDirective to define a directive, and use another tag for "applying" them.
@gqlDirective matches @gqlType, @gqlField etc used to define the other GraphQL concepts.

The GraphQL spec uses the term "annotate" consistently when talking about using directives, so what about @gqlAnnotate?

/**
 * @gqlAnnotate complexity(value:50)
 * or
 * @gqlAnnotate @complexity(value:50)
 */

A GraphQL schema describes directives which are used to annotate various parts of a GraphQL document

In this example, a directive is defined which can be used to annotate a field

Directives can also be used to annotate the type system definition language as well

In this example, the directive @example annotates field and argument definitions

Or, for a more verbose but unmistakable option, @gqlApplyDirective

[captbaritone]

I've confirmed that TypeScript parser will treat

/**
 * @gqlAnnotate @complexity(value:50)
 */

As two separate tags, which is a bummer for us.

[captbaritone]

I'm exploring the ability to use docblock tags as directives directly in this WIP PR: #167

[louy]

Is there anything we can help with to move this forward?

[captbaritone]

I think I have a path forward in the above draft PR. I need to add support for directive validation (surprisingly it's not provided by regular schema validation) and I also want to revisit the API design for applying directives (just using docblock tags might pose an unacceptable tradeoff due to the risk of namespace collisions)

I suspect I'll have time to make progress on Friday.

[captbaritone]

Okay, I made quite a bit of progress today (you can see that progress in this draft PR: #167)

• Add validation for directive arguments which is surprisingly missing from GraphQL-js

Here are a few things I'm stuck on, and could use help thinking of solutions to:

Accessing schema directives at runtime

The graphql-js GraphQLSchema object does not actually preserve schema directives. If your schema is generated from parsing an SDL file, you can dig into the (optional) AST property it exposes, but the GraphQLSchema object Grats generates typegen for does not support a way to specify that, say, a field has a directive on it. This makes it hard to define a proof of concept for how you would actually use these directives.

Syntax for applying directives

My current approach is just to treat docblock tags that match directive names as directives and parse them as SDL. So:

/**
 * @gqlQueryField
 * @cost(credits: 10)
 */
export function greeting(): string {
  return "hello";
}

This is intuitive and simple (no new syntax) but it means if there's ever a namespace collision between docblock tag names you want to use and directive names you want to use, you might get stuck.

I'm going take a stab at the @gqlAnnotate approach proposed above by @leo-fresha:

/**
 * @gqlAnnotate complexity(value:50)
 */