Fix option optimisation compiler bug

[mediremi]

This fixes the compiler bug reported by @jfrolich on Discord:

let foo = (~val1: bool, ~val2: bool) => {
  let a = Some(val1)
  let b = Some(val2)

  switch (a, b) {
  | (_, Some(true))
  | (Some(true), _) => "a"
  | _ => "b"
  }
}

was being compiled to

function foo(val1, val2) {
  return "a";
}

---

The fix is from this Melange PR by @anmonteiro: melange-re/melange#1530 (specifically, commit melange-re/melange@eab306d)

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commit: f203622

[zth]

Great stuff! Thanks to all involved.

[tsnobip]

Thanks a lot @mediremi !

[tsnobip]

And thanks @anmonteiro for the original fix!

[cristianoc]

Is this case actively used in the fix?
Wondering how to make sure there's no infinite loop, whether such an invariant for tables is guaranteed to hold.

[mediremi]

Without this case the boolean example function is not compiled correctly.

[cristianoc]

Then I don't understand the logic. It should be an optimization so omitting a case should not turn on more optimization and get a wrong compilation.
I guess the default case should be false not true.

[cristianoc]

While Normal_optional below, the catch-all case, returns true.
I think it should return false by default, and under certain conditions return true.
So, removing this line should turn off a possibly desired optimization, instead of triggering an incorrect optimization.

[mediremi]

I've made the default case Eval_unknown (no optimisation), and we no longer have a potentially infinite loop 👍