Label argument required on defer/stream directives

[robrichard]

Context

Both the defer and stream directives support a label argument. This label should be used by GraphQL clients to identify the data from patch responses and associate it with the correct fragment. In the Facebook/Relay implementation, a label argument is required by the server schema. Relay is able to automatically generate unique labels, so it is not required for Relay developers to create their own label.

Decision

The spec proposal makes the label argument optional. If provided, the GraphQL Server must add it to the payload.

Consequences

GraphQL clients that need the label argument to function correctly can either generate it or require that it is provided with client side validation.