Prettier 3.6.2
Playground link

--parser babel

Input:

Original source file: https://github.com/prettier/prettier/blob/011791fd6c8856fb92fafec95930e10383ac267b/tests/format/js/last-argument-expansion/dangling-comment-in-arrow-function.js

(
  // foo
) => {}

Output:

() =>
  // foo
  {};

Expected output:

foo(
  (
    // foo
  ) => {},
);

Why?

Should be the same as the input; this is what the user wants