using a variable in a default parameter expression that is shadowed in that function's body causes a reference error

[aweary]

Bug report or Feature request?

Bug report

If you have a default function parameter that refers to a variable, and then you shadow that same variable inside the same function, then Terser confuses the outer variable with the inner one and ends up pointing the default parameter to the inner variable which is not actually in scope yet.

To make that clearer: in the example below database is defined outside of query; the query function has a db parameter which defaults to that outer database variable. Then query defines its own database variable that it accesses the value through.

terser input

var database = { open() { /* ... */ } }

function query(db = database) {
  var database = db;
  database.open();
}

terser output or error
You can see that query(a=e) means its defaulting to the e variable within the query function

var database={open(){}};function query(a=e){var e=a;e.open()}

Expected result
but thats incorrect, it should be defaulting to the outer database value.

var database={open(){}};function query(a=database){var e=a;e.open()}

[dasa]

This looks similar to #1478

[fabiosantoscode]

Yes, it's duplicated. The next quarter I'll be working on this