Input

const App = () => {
  return (
    <O>
      <I>
        <x />
        {f(xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx).y} (
        {label})
      </I>
    </O>
  );
};

Config

{}

Oxfmt output

const App = () => {
  return (
    <O>
      <I>
        <x />
        {
          f(xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx).y
        } (
        {label})
      </I>
    </O>
  );
};

Prettier output

const App = () => {
  return (
    <O>
      <I>
        <x />
        {f(xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx).y} (
        {label})
      </I>
    </O>
  );
};

Additional notes

The line {f(xxx...xxx).y} ( is exactly 79 characters at 8-space indent — fits within printWidth: 80. Prettier leaves it on a single line. oxfmt expands the JSX expression {f(xxx...).y} across three lines ({, content, } on separate lines), apparently treating the trailing ( literal text as part of the same group's measurement and deciding the combined sequence doesn't fit.

The <x /> self-closing element is necessary to set up the printer state that exposes the bug — it produces the hard line break preceding the trigger expression that resets the printer's "measured group fits" tracking, so the inner expression group ends up re-measuring itself and walking past the fill entry boundary into subsequent content.

Tested against oxfmt 0.47.0 and prettier 3.8.3.