Stream on scalar lists

[robrichard]

Context

Originally posted by @michaelstaib graphql/graphql-spec#742 (review)

When streaming a field that has a list of composite types the iterator will yield objects like the following:

{
  "id": "1000",
   "name": "Luke Skywalker"
}

These will than be integrated into a result that could look like the following:

{
  "path": ["hero", "friends", "nodes", 1],
  "data": {
    "id": "1000",
    "name": "Luke Skywalker"
  },
  "hasNext": false
}

This works quite well... But what if the list is a list of leaf values like a list of strings? I have the same issue with a nested list where the element is actually a list of something.

Can data in this case be a scalar or a list? Would this break the contract for GraphQL results?

Decision

Current implementation in graphql-js returns scalar fields. It needs to be clarified in the spec PR that this is possible

{
  data: {
    scalarList: ['apple'],
  },
  hasNext: true,
},
{
  data: 'banana',
  path: ['scalarList', 1],
  hasNext: true,
},
{
  data: 'coconut',
  path: ['scalarList', 2],
  hasNext: false,
},

Consequences

Clients should not assume data will always be a map type when @stream is used on scalar fields.

Status

• defined in spec
• implemented in graphql-js

[robrichard]

Discussed during Dec 2021 WG meeting. Agreement that data can be a scalar (or a list for multidimensional list fields). Spec can be updated to define data not as a map, but as the type of the referenced field (or query type for root field).

[glasser]

Note for posterity: this has been changed by #32 (and may change more by #42)