Label name not checked and incorrect code emitted for label in external definition

[cknitt]

This:

@send external reduce: (array<'b>, ('a, 'b) => 'a, ~initialValue: 'a=?) => 'a = "reduce"
let reduce = (arr, initialValue, f) => reduce(arr, f, ~initialValue)

compiles fine:

function reduce(arr, initialValue, f) {
  return arr.reduce(f, initialValue);
}

However, when I change the label name:

@send external reduce: (array<'b>, ('a, 'b) => 'a, ~wrongLabelName: 'a=?) => 'a = "reduce"
let reduce = (arr, initialValue, f) => reduce(arr, f, ~initialValue)

1. the code compiles (which it shouldn't, because the label name does not match)
2. I get the following incorrect output (v12):

function reduce(arr, initialValue, f) {
  return arr.reduce(f)(initialValue);
}

[cknitt]

In v11, the problem exists, too, and the output is

function reduce(arr, initialValue, f) {
  return Curry._1(arr.reduce(f), initialValue);
}

[cristianoc]

Here's a small repro without externals:

let r: (string, ~wrongLabelName: int=?) => 'a = (_s, ~wrongLabelName=3) => {
  let _ = wrongLabelName
  assert(false)
}

let tst1 = r("", ~initialValue=2)
let tst2 = r("")(~initialValue=2)

We have that tst1 is treated the same as tst2.

Though with the following type annotation, only tst1 fails type checking, so they're not always treated the same:

let r: (string, ~wrongLabelName: int=?) => ((~initialValue:int) => int)