mutationType not working on type policies declaration

[zaguiini]

Intended outcome:
To use a different mutation root type than Mutation.

Actual outcome:
Setting mutationType to true on the custom mutation type does not make any difference and Apollo attempts to write cache to Mutation instead of the desired one.

How to reproduce the issue:
It's proprietary code. I'll try my best to describe.
Root mutation is called TalentMutation. I've set:

{
  TalentMutation: {
    mutationType: true,
    fields: {
      talentPortalSetting: { merge: false }
    }
  }
}

Throws the following warning:

To address this problem (which is not a bug in Apollo Client), either ensure all objects of type TalentPortalSettingOps have an ID or a custom merge function, or define a custom merge function for the Mutation.talentPortalSetting field, so InMemoryCache can safely merge these objects.

Versions

  System:
    OS: macOS 10.15.7
  Binaries:
    Node: 14.8.0 - ~/.nvm/versions/node/v14.8.0/bin/node
    Yarn: 1.22.5 - ~/.nvm/versions/node/v14.8.0/bin/yarn
    npm: 5.1.0 - ~/Development/toptal/talent-portal-frontend/node_modules/.bin/npm
  Browsers:
    Chrome: 87.0.4280.88
    Edge: 87.0.664.57
    Firefox: 83.0
    Safari: 14.0
  npmPackages:
    @apollo/client: ^3.3.4 => 3.3.4
    apollo-upload-client: ^14.1.3 => 14.1.3

Additional information

It's properly working on 3.2.9. Not sure what's changed. I haven't seen anything relevant on the CHANGELOG, so it must be something changed by accident.

[benjamn]

@zaguiini If you have a chance to try a manual binary-ish search, it would be useful to know which beta version of v3.3 introduced the regression. We had 18 betas (@apollo/client@3.3.0-beta.0 through -beta.17) and 6 RCs (-rc.0 through -rc.5). I don't know if there's a good way to use git bisect for this, but once you have a quick way to detect the problem, you can try a few of those versions and hopefully narrow things down from there. Let me know if you encounter anything weird/surprising along the way!

[zaguiini]

Hey @benjamn, it was 3.3.0-beta.3 which introduced the regression. I'll try and find what went wrong.

EDIT: This is the commit which includes changes from beta 2 to beta 3. I think the problem lies on policies.ts changes, but I haven't got the time to investigate it further.

[benjamn]

@zaguiini Thanks! That's a very useful clue for my investigation. 🙏

[benjamn]

This should be fixed in @apollo/client@3.3.6 (just published). Please feel free to reopen if you're still having issues. Thanks!