Incorrect JS outputs when pattern matching with empty list

[dsiu]

Starting from alpha.5 (up to the current alpha.7), the following code generates incorrect js output:

let isEmpty: 'a. list<'a> => bool = x =>
  switch x {
  | list{} => true
  | _ => false
  }

let isNotEmpty: 'a. list<'a> => bool = xs => !isEmpty(xs)

Incorrect JS output (Playground):

// Generated by ReScript, PLEASE EDIT WITH CARE

function isEmpty(x) {
  return !x;
}

function isNotEmpty(xs) {
  return xs;
}

export {
  isEmpty,
  isNotEmpty,
}
/* No side effect */

Whereas alphe.4 and before generates correctly (Playground):

// Generated by ReScript, PLEASE EDIT WITH CARE


function isEmpty(x) {
  if (x) {
    return false;
  } else {
    return true;
  }
}

function isNotEmpty(xs) {
  return !(
    xs ? false : true
  );
}

export {
  isEmpty,
  isNotEmpty,
}
/* No side effect */

I found out this problem when porting [Relude](https://github.com/dsiu/rescript-relude) to rescript@v12. The following Jest tests fails:

 test("isNotEmpty is false for empty list", () => expect(List.isNotEmpty(list{}))->toBe(false))

 test("isNotEmpty is true for non-empty list", () => expect(List.isNotEmpty(list{1}))->toBe(true))

Summary of all failing tests
 FAIL  __tests__/Relude_List_test.bs.js
  ● List › isNotEmpty is false for empty list

    expect(received).toBe(expected) // Object.is equality

    Expected: false
    Received: 0

      at affirm (node_modules/@glennsl/rescript-jest/src/jest.bs.js:73:36)
      at Object.<anonymous> (node_modules/@glennsl/rescript-jest/src/jest.bs.js:220:5)

  ● List › isNotEmpty is true for non-empty list

    expect(received).toBe(expected) // Object.is equality

    Expected: true
    Received: {"hd": 1, "tl": 0}

      at affirm (node_modules/@glennsl/rescript-jest/src/jest.bs.js:73:36)
      at Object.<anonymous> (node_modules/@glennsl/rescript-jest/src/jest.bs.js:220:5)

Thank you for filing! Check list:

• Is it a bug? Usage questions should often be asked in the forum instead.
• Concise, focused, friendly issue title & description.
• A minimal, reproducible example.
• OS and browser versions, if relevant.
• Is it already fixed in master? Instructions

[cristianoc]

The previous output if(x) ... was one boolean compiler optimisation away from the problem.
Addressed in #7237