[2022-12] Revise IsVariableUsageAllowed to forbid nullable variable with default usage in non-nullable list position

[benjie]

Action: having default mode be the happy path which will require to spec text changes

Relates to: graphql/graphql-spec#1002

We should move IsVariableUsageAllowed as IsVariableUsageAllowedLegacy in an appendix (or an addendum within the section) and add a new IsVariableUsageAllowed that turns this issue from a runtime error to a validation error. Use IsVariableUsageAllowedLegacy if you need to support legacy queries.

Video: https://youtu.be/nkPn-F_UBJo?list=PLP1igyLx8foH30_sDnEZnxV_8pYW3SDtb&t=2702
Actual action item timestamp: https://youtu.be/nkPn-F_UBJo?list=PLP1igyLx8foH30_sDnEZnxV_8pYW3SDtb&t=3452

• assignee(s): @benjie
• source: https://github.com/graphql/graphql-wg/blob/main/notes/2022/2022-12.md#field-error-resulting-from-insufficient-validation-of-variables-15m-benjie

---

Note: Action Item issues are reviewed and closed during Working Group
meetings.

[benjie]

Spec changes: graphql/graphql-spec#1059

Added to the WG meeting next week.

[benjie]

Discussed at today's WG; closing 👍