__DirectiveLocation for directives

[sungam3r]

I propose to add one more location into __DirectiveLocation enumeration: DIRECTIVE_DEFINITION. Relates to #300. Logically, nothing prevents directives from being applied to the directives themselves. Of course, parser support is required.

directive @important on DIRECTIVE_DEFINITION
directive @statusquo on FIELD_DEFINITION @important


type User {
  id: ID!
  name: String @statusquo
  admin: Boolean!
}

type Query {
  user: User
}

[peldax]

Hi, I agree with your proposal 👍.

One simple note, isn't DIRECTIVE_DEFINITION more suitable in this case? Although directives cannot be applied to "directive usages" in executable document (at least not without some new additional syntax), I think its good idea to explicitly state its meant only to definitions.

[sungam3r]

Of course it is. Changed.

[martinbonnin]

2 use cases:

Opt-in markers:

directive @optIn

# optIn usage defines @experimentalDeploymentApi as an opt-in marker
directive @experimentalDeploymentApi @optIn

Identifying client side directives:

directive @client
directive @catch @client