Using Array and Boolean in condition does not trigger a warning

TypeScript Version: 3.8.0-dev.20200115

Search Terms: overlap boolean vs array condition

Code

function isAllowed() {
  const myCondition = false;
  if (myCondition === false) {
    return [];
  }

  return true;
}

if (isAllowed()) {
  // boolean and array will results in a "true" condition
  console.log('allowed');
} else {
  // never reached
  console.log('not allowed');
}

Expected behavior:

• Seeing a message saying something like This condition can produce unexpected results since the types 'boolean' and 'array' have no overlap (not really good but you get the idea)

Actual behavior:
I won't say that it's a bug, but something that could be improved. I know that it's valid javascript but this a bug in the code that should/could be prevented by Typescript

• Typescript does not complain that comparing boolean and array can results in bad condition

Already fixable by

• It does complain if you write if (isAllowed() === true) but it's easy to not do it.

Playground Link: http://www.typescriptlang.org/play/?ts=3.8.0-dev.20200115&ssl=1&ssc=1&pln=15&pc=1#code/GYVwdgxgLglg9mABDAzgQQDYbgdwKYAmAFAJSIDeAUIohAilIgLYCeAwggTLAogLyIoAJxB4A3NWTBERVhzBceSPisEi8ZKjRpC8UEEKQBtALoSaAX0qTd+w4mABDDCnGUrlGNKKpM2fMQkmpJ0YChwGHgAdNgA5kQA5M7+hAkkEhaIeC54FCH0EdFxiWBwjMm4qenulEA

Commencez par reproduire le comportement dans le TypeScript Playground lié, à l’aide de l’exemple fourni et du comportement actuel du compilateur. Suivez le chemin de vérification des types pour les conditions impliquant des valeurs booléennes et des tableaux ; le travail est terminé lorsqu’un diagnostic approprié est produit pour la condition incompatible sans rejeter les modèles JavaScript valides.