@inline fragments on unions does not work

[zth]

Symptom: You have an @inline fragment on a union type, but you're never getting anything but #UnselectedUnionMember back. Example:

fragment MetricValueUtilsValue_value on MetricValues @inline {
    ... on MetricValueCount {
      count
    }
    ... on MetricValueCurrency {
      amount
    }
    ... on MetricValuePercentage {
      percentage
    }
  }

Cause: Automatic insertion of __typename selection seems to not work on @inline fragments on unions.

Current workaround: add the __typename selection yourself.

fragment MetricValueUtilsValue_value on MetricValues @inline {
+   __typename
    ... on MetricValueCount {
      count
    }
    ... on MetricValueCurrency {
      amount
    }
    ... on MetricValuePercentage {
      percentage
    }
  }