fix: ensure default directives do not get replaced by custom directives

[jmauerhan]

Proposed changes

• This PR fixes a bug where our custom directives for federation were replacing the default directives, making queries which included include or skip not work correctly - the underlying webonyx/graphql-php library would throw this error: "Unknown directive \"include\".
• By merging the custom directives with the standard ones, we now have all of the required directives.

How to test

• In addition to unit tests, I tested locally with a federated schema. This fix allowed a query which used @include across a federated schema to properly resolve.

Can also confirm by running this query to see the directives:

query{
  __schema{
    directives{
      name
    }
  }
}

before:

{
  "data": {
    "__schema": {
      "directives": [
        {
          "name": "key"
        },
        {
          "name": "external"
        },
        {
          "name": "requires"
        },
        {
          "name": "provides"
        }
      ]
    }
  }
}

with the fix:

{
  "data": {
    "__schema": {
      "directives": [
        {
          "name": "key"
        },
        {
          "name": "external"
        },
        {
          "name": "requires"
        },
        {
          "name": "provides"
        },
        {
          "name": "include"
        },
        {
          "name": "skip"
        },
        {
          "name": "deprecated"
        }
      ]
    }
  }
}

Unit Tests

• This PR has unit tests
• This PR does not have unit tests: why?

[xiian]

👍

To provide a bit more context:

With webonyx/graphql-php, The directives are typically accessed via Schema::getDirectives(), which will return the directives from the config OR GraphQL::getStandardDirectives(), which calls Directive::getInternalDirectives() just like this PR.

And since we are defining directives on the config, we would need to include the internal directives as well.

There may be a case made for using GraphQL::getStandardDirectives() instead of Directive::getInternalDirectives(), but I don't see any value in the extra step right now.

[jmauerhan]

There may be a case made for using GraphQL::getStandardDirectives() instead of Directive::getInternalDirectives(), but I don't see any value in the extra step right now.

I actually had that first, but since it's using array_values, we lose the key names (which are the directive names), so it doesn't work well here.

public static function getStandardDirectives() : array
{
    return array_values(Directive::getInternalDirectives());
}