Issues with $let since 6.2.0

[abarthen]

When trying to upgrade from 6.1.3 I am experiencing issues with queries that should work. $let seems to be one source of this, though apparently not the only one - replacing the 6.2.X version of $let with the 6.1.3 version prevents the query from crashing but the result is still wrong.

I have this example query which works in the mongo playground and also worked prior to 6.2.0:
https://mongoplayground.net/p/Yf2QrwCX7Sf

If I log what let.js does I get {e: "t"} as variables, which makes sense since the first element in the list I check is the string "string", so the element at index 1 is "t". But I then get the error Use of undefined variable: e and execution stops.

Using the code from 6.1.3 for $let fixes this and the result of $let is correct but the endresult is still wrong (no element gets returned), so there are apparently more issues elsewhere.

[kofrasa]

Thanks for the report @abarthen. I think it was introduced in the refactor to separate variables from the actual document for processing.