__resolveType and __isTypeOf do not support Promise as return value

[marcoreni]

Describe the bug
GraphQL supports returning promise for __resolveType and __isTypeOf (for interfaces and unions) since graphql/graphql-js#631, but code generator does not support it.

1. My GraphQL schema:

interface Item {
}

3. My codegen.yml config file:

overwrite: true
schema: "./schemas/schema.gql"
documents: null

generates:
  src/types.ts:
    plugins:
      - "typescript"
      - "typescript-resolvers"
    config:
      useIndexSignature: true

Expected behavior
Generated code for TypeResolveFn and isTypeOfResolverFn should include the Promise as a result, similar to what it's done for ResolverFn.

[dotansimha]

Working on a fix in: #3599

@marcoreni can you please try the alpha version? 1.12.3-alpha-47f7aea4.101

[marcoreni]

I tested the alpha version and it seems to work.

Thanks, @dotansimha !

[dotansimha]

Available in v1.13.0