Questionable formatting for chained conditional types in TypeScript

Prettier 1.14.2 Playground link

--parser typescript

Input:

let x = one instanceof two ? three : four instanceof five ? six : seven instanceof eight ? nine : ten;

type x = one extends two ? three : four extends five ? six : seven extends eight ? nine : ten;

Output:

let x =
  one instanceof two
    ? three
    : four instanceof five
      ? six
      : seven instanceof eight
        ? nine
        : ten;

type x = one extends two
  ? three
  : four extends five ? six : seven extends eight ? nine : ten;

Expected behavior:

I know there’s some open discussion in https://github.com/prettier/prettier/issues/737 around exactly how chained ternary expressions should be formatted, but no matter the outcome there, I think I would expect chained conditional types to be formatted the same way.

It seems as though the formatting for chained conditional types prefers to keep as much content on the final line as possible, which ends up giving more visual weight to some branches than others and leading to some weird readability issues. As far as I can tell, chained ternaries don’t exhibit this behavior—as soon as the chain is forced to break across lines, the whole thing cascades.

[suchipi]

Sorry for the late response, I’ve been pretty busy. My intention with that PR was to treat conditional types the same way, so I would consider it in-scope.

[dfreeman]

@suchipi Just a friendly ping—totally understand if this is out of scope for #5039, but want to make sure this doesn’t get lost if that’s the case 🙂