document.populate() throws when populating immutable array of refs with String IDs

[ThoseGrapefruits]

Do you want to request a feature or report a bug?

Report a bug, possibly related or at least adjacent to #10159.

What is the current behavior?

When trying to populate an array of immutable refs, whose reference ID type is String, mongoose throws the following error:

/Users/l/Desktop/node_modules/mongoose/lib/schema/array.js:392
        throw new CastError('[' + e.kind + ']', util.inspect(value), this.path + '.' + i, e, this);
              ^

CastError: Cast to [string] failed for value "["chicken"]" (type string) at path "friends.0"
    at SchemaArray.cast (/Users/l/Desktop/node_modules/mongoose/lib/schema/array.js:392:15)
    at convertTo_id (/Users/l/Desktop/node_modules/mongoose/lib/helpers/populate/getModelsMapForPopulate.js:515:28)
    at getModelsMapForPopulate (/Users/l/Desktop/node_modules/mongoose/lib/helpers/populate/getModelsMapForPopulate.js:242:13)
    at populate (/Users/l/Desktop/node_modules/mongoose/lib/model.js:4399:21)
    at _populate (/Users/l/Desktop/node_modules/mongoose/lib/model.js:4370:5)
    at /Users/l/Desktop/node_modules/mongoose/lib/model.js:4347:5
    at promiseOrCallback (/Users/l/Desktop/node_modules/mongoose/lib/helpers/promiseOrCallback.js:9:12)
    at Mongoose._promiseOrCallback (/Users/l/Desktop/node_modules/mongoose/lib/index.js:1149:10)
    at Function.Model.populate (/Users/l/Desktop/node_modules/mongoose/lib/model.js:4345:23)
    at model.populate (/Users/l/Desktop/node_modules/mongoose/lib/document.js:3940:19)
    at /Users/l/Desktop/node_modules/mongoose/lib/document.js:4018:10
    at /Users/l/Desktop/node_modules/mongoose/lib/helpers/promiseOrCallback.js:31:5
    at new Promise (<anonymous>)
    at promiseOrCallback (/Users/l/Desktop/node_modules/mongoose/lib/helpers/promiseOrCallback.js:30:10)
    at model.Document.execPopulate (/Users/l/Desktop/node_modules/mongoose/lib/document.js:4017:10)
    at run (/Users/l/Desktop/repro.js:31:35) {
  stringValue: '"["chicken"]"',
  messageFormat: undefined,
  kind: '[string]',
  value: '["chicken"]',
  path: 'friends.0',
  reason: CastError: Cast to string failed for value "["chicken"]" (type CoreMongooseArray) at path "friends"
      at SchemaString.cast (/Users/l/Desktop/node_modules/mongoose/lib/schema/string.js:603:11)
      at SchemaString.SchemaType.applySetters (/Users/l/Desktop/node_modules/mongoose/lib/schematype.js:1106:12)
      at SchemaArray.cast (/Users/l/Desktop/node_modules/mongoose/lib/schema/array.js:388:29)
      at convertTo_id (/Users/l/Desktop/node_modules/mongoose/lib/helpers/populate/getModelsMapForPopulate.js:515:28)
      at getModelsMapForPopulate (/Users/l/Desktop/node_modules/mongoose/lib/helpers/populate/getModelsMapForPopulate.js:242:13)
      at populate (/Users/l/Desktop/node_modules/mongoose/lib/model.js:4399:21)
      at _populate (/Users/l/Desktop/node_modules/mongoose/lib/model.js:4370:5)
      at /Users/l/Desktop/node_modules/mongoose/lib/model.js:4347:5
      at promiseOrCallback (/Users/l/Desktop/node_modules/mongoose/lib/helpers/promiseOrCallback.js:9:12)
      at Mongoose._promiseOrCallback (/Users/l/Desktop/node_modules/mongoose/lib/index.js:1149:10)
      at Function.Model.populate (/Users/l/Desktop/node_modules/mongoose/lib/model.js:4345:23)
      at model.populate (/Users/l/Desktop/node_modules/mongoose/lib/document.js:3940:19)
      at /Users/l/Desktop/node_modules/mongoose/lib/document.js:4018:10
      at /Users/l/Desktop/node_modules/mongoose/lib/helpers/promiseOrCallback.js:31:5
      at new Promise (<anonymous>)
      at promiseOrCallback (/Users/l/Desktop/node_modules/mongoose/lib/helpers/promiseOrCallback.js:30:10) {
    stringValue: '"["chicken"]"',
    messageFormat: undefined,
    kind: 'string',

[ truncated ]

If the current behavior is a bug, please provide the steps to reproduce.

Repro script:

const mongoose = require('mongoose');

const Cat = mongoose.model('Cat', {
  _id: { 
    type: String,
  },

  name: String,

  friends: [ {
    immutable: true,
    ref: 'Cat',
    type: String
  } ]
});

async function run() {
  await mongoose.connect('mongodb://localhost:27017/test', {
    useNewUrlParser: true,
    useUnifiedTopology: true
  });
  
  await mongoose.connection.dropDatabase();

  const friend = new Cat({ _id: 'chicken', name: 'Chicken' });
  await friend.save();

  const myCat = new Cat({ _id: 'waffle', name: 'Waffle', friends: [ friend.id ] });
  await myCat.save();

  await myCat.populate('friends').execPopulate();
}

run().then(() => process.exit(0));

What is the expected behavior?

This should run without an error, and the first entry in friends should be populated.

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.

Node 15.14.0
Mongoose 5.12.10
MongoDB 4.4.6

[IslandRhythms]

I'm not getting an identical error to yours but I am getting a similar error.

(node:2552) UnhandledPromiseRejectionWarning: CastError: Cast to [string] failed for value "["chicken"]" (type string) at path "friends.0"
    at SchemaArray.cast (C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\schema\array.js:392:15)
    at convertTo_id (C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\helpers\populate\getModelsMapForPopulate.js:515:28)
    at getModelsMapForPopulate (C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\helpers\populate\getModelsMapForPopulate.js:242:13)
    at populate (C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\model.js:4399:21)
    at _populate (C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\model.js:4370:5)
    at C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\model.js:4347:5
    at promiseOrCallback (C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\helpers\promiseOrCallback.js:9:12)
    at Mongoose._promiseOrCallback (C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\index.js:1149:10)
    at Function.Model.populate (C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\model.js:4345:23)
    at model.populate (C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\document.js:3940:19)
    at C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\document.js:4018:10
    at C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\helpers\promiseOrCallback.js:31:5
    at new Promise (<anonymous>)
    at promiseOrCallback (C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\helpers\promiseOrCallback.js:30:10)
    at model.Document.execPopulate (C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\node_modules\mongoose\lib\document.js:4017:10)
    at run (C:\Users\Daniel Diaz\Desktop\Work\debugging\JavaScript\10264.js:31:35)
(Use `node --trace-warnings ...` to show where the warning was created)
(node:2552) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 2)
(node:2552) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.