Closure TDZ

[kaleidawave]

Current TDZ finding is solved for standard statements AND for functions (as well as all things function-like). (thanks to #69 these errors have positions!)

This works for conditional function calls

function get_x() {
  return x
}

if (Math.random() > 0.5) {
  // Emits a TDZ error 'Variable 'x' used before declaration'
  get_x()
}

let x = 5;

---

However as it turns out with closures, TDZ issues are non-deterministic on their reference

let obj = {};
function closure3() {
    obj.get_z = () => {
        return z
    };

    if (Math.random() > 0.5) {
        return;
    }

    let z = 0;
}

closure3();
return obj.get_z()

Half the time this leaks a reference that never gets declared. Somehow we want to catch this mistake.

Things to think about

• How does this work with unknown conditional interruptions
  • Even if the error occurs 1% of the time (changing the above to Math.random() > 0.99). It needs to error
• How does this work with unknown interruptions (calling poly functions, which are neither known to be pure or impure in relation to throw events).
• How can this provide good errors
  • Purely raising at function calling sites doesn't benefit checking libraries
  • Maybe a warning can occur?

At some point I think this can't fully support JavaScript and instead sit in a local minimum

[kaleidawave]

Had some thoughts: Instead it will be probably be solved the same way as find_possible_mutations. When a function is leaked outside the function it was defined it, it should run a similar Rust function to find_possible_mutations which checks any free_variables are defined. Thus avoiding any Event stuff