[the following works perfectly in the [legacy] Mongo Shell 4.4 for MongoDB 4.4]

mongosh throws an error when attempting to create a view based on agg pipeline which uses $function operator. The view can't be created as a result.

Docs for $function: https://docs.mongodb.com/manual/reference/operator/aggregation/function/

(issue may also affect $accumulator https://docs.mongodb.com/manual/reference/operator/aggregation/accumulator/ too - I've not tested that). 

Steps to reproduce (using mongosh 0.7.7 connected to a MongoDB 4.4+ DB running on localhost):

db.persons.drop();

db.persons.insertOne({
    'name': 'John Smith',
});

db.persons.find();

var pipeline = [
    {'$set': {
        'name_md5': {'$function': {'lang': 'js', 'args': ['$name'], 'body':                   
            function(val) {
                return hex_md5(val);
            }
        }},
    }},
];

db.persons.aggregate(pipeline);

db.persons_view.drop();

db.createView('persons_view', 'persons', pipeline);   // ERROR!!!!

db.persons_view.find();

When you run this in mongosh, the createView() command above (penultimate line of code) results in following mongosh error being displayed:

MongoError: Invalid pipeline for view testdata.persons_view :: caused by :: Invalid $set :: caused by :: The body function must be specified.

It seams somehow that mongosh is losing the 'body' field from the $function declared in the pipeline.