Single field subscriptions validator has conflicts with the spec

[nikis05]

The rule: https://github.com/graphql/graphql-js/blob/master/src/validation/rules/OverlappingFieldsCanBeMergedRule.js

The spec states that subscriptions should have a single root field. Current implementation only checks that there is one selection on selection set of the subscription, not taking fragments into account. If a single selection is a fragment spread or an inline fragment (with multiple fields) this rule will wrongfully pass.

[kshitij86]

I would like to look into this issue and work on a fix. @IvanGoncharov can I please get assigned to solve this bug?

[benjie]

I noticed this too; whoever fixes this, please can you ping me on #2861 as I'll need to incorporate the fix into that PR.

[benjie]

I may have resolved this bug as part of #2861

[yaacovCR]

@benjie can this be closed?

[benjie]

I believe so 👍