Fix cache normalization for mixed fields

[dferber90]

Summary

Given a query

query {
  animals {
    species {
      name
    }
  }
}

which gets executed twice where species could either be of GQL type Dog or Cat, and where the responses have the species types inlined with no dataId and occur sequentially, in this order:

animals: [{
  __typename: 'Animal',
  species: {
    __typename: 'Cat',
    name: 'cat',
  },
}],

animals: [{
  __typename: 'Animal',
  species: {
    __typename: 'Dog',
    name: 'dog',
  },
}],

the store should finally contain

{
  '$ROOT_QUERY.animals.0.species': { name: 'dog' },
  ROOT_QUERY: {
    animals: [{
      generated: true,
      id: 'ROOT_QUERY.animals.0',
      type: 'id',
      typename: 'Animal',
    }],
  },
  'ROOT_QUERY.animals.0': {
    species: {
      generated: true,
      id: '$ROOT_QUERY.animals.0.species',
      type: 'id',
      typename: 'Dog',
    },
  },
}

However, without this PR it would wrongly contain '$ROOT_QUERY.animals.0.species': undefined (and some other stuff).

Description

It seems that the cache attempted to do cleanup of a generated object in case the reference to it gets replaced with one where we're actually provided a non-generated id. However, this also ran when a generated object's type changed, thus accidentally removing the newly generated object.

Details are in #3419

closes #3419

[dferber90]

🤕 This bug is still relevant and causing us issues in production

It would be helpful to get a rough idea on when somebody will get to review this, so that we can figure out whether it's worth to create a workaround in the meantime.

Thanks!

[dferber90]

It has been two weeks :( Anyone?

[tdeekens]

This is now affecting us too.

[n1ru4l]

@jbaxleyiii

[hwillson]

At a first quick glance this looks awesome @dferber90 - thanks very much for working on this! I've slotted this in for a more thorough review, and will have updates to you shortly. 🤞 this should be merged in sometime tomorrow (and will be included in next Tuesday's release).

[hwillson]

This all looks great @dferber90 - thanks very much for your work on this. LGTM!

[dferber90]

🎈Excellent, thanks for taking the time! I'm looking forward to the release