Is transform working in publishComposite expected behaviour?

[jrkinclus]

Describe the bug
The Meteor docs say that transform is not applied to Cursors returned from publications. So, if one wanted to not publish individual elements in an array field, they can't do this:

// Publication that wants to omit individual elements from an array field
Meteor.publish('myPub', function () {
  return MyCollection.find({}, {
    transform: (obj) => {
      // This function never gets called, so this won't work
      obj.someArrayField = obj.someArrayField.filter(element => element !== 'someValue');
      return obj;
    },
  });
});

However, this does work:

// Publication that wants to omit individual elements from an array field
Meteor.publishComposite('myCompositePub', function () {
  return {
    find() {
      return MyCollection.find({}, {
        transform: (obj) => {
          // This function does get called and modifies the published object
          obj.someArrayField = obj.someArrayField.filter(element => element !== 'someValue');
          return obj;
        },
      });
    },
  };
});

Expected behavior
I would've expected the transform to not work for publishComposite too. Is this intended behaviour or an accidental feature?

Tested on
v1.8.6

[github-actions]

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[jrkinclus]

The main question I have is whether this behaviour will be kept or removed in future versions; can I make use of transform in publishComposite pubs without fear a future version update breaking the code?

[manueltimita]

Like you said, historically, transforms have not been supported in publication cursors and evidence of that can still be found in old forum threads,. Funnily the docs for 2.16 and 3.x have no mention of it anymore, so perhaps something has changed.

If it works in publish-composite it means it is a side effect of it being supported in Meteor.js. From what I could tell while migrating the package to Meteor 3, there is nothing in the code in this regard.