Don't force arrow function body on same line

I created a function like this:

const promiseFromCallback = fn => 
  new Promise((resolve, reject) => 
    fn((err, result) => {
      if (err) return reject(err);
      return resolve(result);
    })
  );

This seems pretty clear to me with all the arrow function bodies moved to a new line. Prettier formats that function to this:

const promiseFromCallback = fn => new Promise((resolve, reject) => fn((
  err,
  result
) => {
  if (err) return reject(err);
  return resolve(result);
}));

At least to me that is a lot less readable than the first one. This formatting seems to be related to always moving the body of an arrow function to the same line as the arrow. I’m not sure this creates well formatted code.

I also added that code to prettier.github.io

[vjeux]

#847 makes it look:

const promiseFromCallback = fn =>
  new Promise((resolve, reject) => fn((err, result) => {
    if (err) return reject(err);
    return resolve(result);
  }));

instead. It’s not the original one but looks way less broken than what is currently in prettier.

[vjeux]

Thanks for the report! This is not intended to be printed like this. #674 and #680 are attempts at fixing the problem but we’re not 100% sure what the root cause is.