Add options to retain lines which helps babel to preserve newlines/whitespace

[levibuzolic]

Implements a --retain-lines option to pass through to Babel's retainLines option. This allows Babel to try and preserve line positions when generating output code -- the resulting output can be quite ugly, but prettier does a great job of cleaning it up.

Input

import type { Something } from "Source";

type Another = {|
  key: string,
|};

/*
 * This is a comment
 */

// Another comment

function Hello() {
  const example = 1;

  return null
}

Output

Before	After
import type { Something } from "Source"; type Another = { key: string; }; /* * This is a comment */ // Another comment function Hello() { const example = 1; return null; }	import type { Something } from "Source"; type Another = { key: string; }; /* * This is a comment */ // Another comment function Hello() { const example = 1; return null; }

Fixes #237

[GunnarMM]

Looks good to me. I have also used your PR to convert a big enterprise app and it did its job brilliantly!

[DeadManPoe]

@GunnarMM My company would benefit a lot from this, but I see this project has not had any new commits in the master branch since April 2021. How likely is this going to be merged?

[MasonChinkin]

😢 wish we could merge this @GunnarMM

[GunnarMM]

Merging is blocked. I don't have power here. Maybe @levibuzolic can take a look at the merge requirements

[levibuzolic]

@MasonChinkin @GunnarMM @DeadManPoe given the specs don't run anymore and there hasn't been a PR merge or release in 2+ years I don't think it's going to happen.

But if you do want to use flow-to-ts with this change included, you can pull down my fork and just run it directly and target your codebase or whatever folder of your choice.

This retain lines feature is far from perfect and we found it did shift a few of our comments up a line in a few places, but it was definitely an improvement over the default behaviour.