[RFC] Directive proposal for opting out of null bubbling

[benjie]

This PR builds on #1048, so you should see the diff from that PR:

benjie/graphql-spec@asterisk...benjie:graphql-spec:no-null-bubbling

This introduces a directive on operations that disables the null/error propagation behavior by treating all Non-Null types as if they were Null-Only-On-Error types (see #1048).

The specific name of this directive (currently @nullOnError) is open to workshopping:

• @noBubblesPlz 😉 or @tepid 🤣
• @disableNullPropagation / @disableErrorPropagation / @noNullPropagation / @noPropagation / etc
• @localErrors
• @dontHandleErrorsForMeIKnowWhatImDoing
• {your suggestion here}

This PR currently only includes a description of the directive and an example; the implementation is yet to come (hence: draft).

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[bbakerman]

in terms of naming - we have a proposed PR on graphql-java

graphql-java/graphql-java#3772

@errorHandling(onError : NULL) or @errorHandling(onError : PROPOGATE)

This is not merged (yet) but its a name suggestion I would like to link here

[benjie]

Another option:

enum __ErrorBehavior {
  """
  Non-nullable positions that error cause the error to propagate to the nearest nullable
  ancestor position. The error is added to the "errors" list.
  """
  PROPAGATE
  
  """
  Positions that error are replaced with a `null` and an error is added to the "errors"
  list.
  """
  NULL
  
  """
  If any error occurs, abort the entire request and just return the error in the "errors"
  list. (No partial success.)
  """
  ABORT
  
  """
  Positions that error are replaced with an inline representation of the error, and
  the path to the error is added to the "errorPaths" list.
  """
  INLINE
}

directive @behavior(onError: __ErrorBehavior! = PROPAGATE) on QUERY | MUTATION | SUBSCRIPTION

(To be clear: I'm not proposing to implement ABORT or INLINE - these are just examples to justify why we might consider using an enum rather than a boolean.)

Rather than going error-centric for this, I felt like a single directive to handle many behaviors might make sense. We could later expand this so that you can do things like @behavior(onDeprecated: ERROR, onError: ABORT).