feat: only save files if they are unchanged

[kentcdodds]

Closes #320

This also solves a significant annoyance for anyone using postcss with an app that rebuilds on file change: remix-run/remix#714

[RyanZim]

Hey, code looks good; my only concern is performance. Has any testing been done on this?

[kentcdodds]

Just did some testing here:

const fs = require("fs-extra");

async function oneFile() {
  console.time("one file");
  await fs.readFile("./files/01.css");
  console.timeEnd("one file");
}

async function hundredFiles() {
  console.time("100 files");
  for (let i = 0; i < 100; i++) {
    await fs.readFile(`./files/01 copy ${i}.css`);
  }
  console.timeEnd("100 files");
}

oneFile();
hundredFiles();

Those css files are each 111kb of this copy/pasted over and over:

body {
  color: red;
}

My output (on my fast machine) is:

one file: 0.557ms
100 files: 15.627ms

It's pretty darn fast. Feel free to watch for yourself (I'm live streaming right now): https://www.youtube.com/watch?v=KPKBUBchCVo

So I think this is fine. Though if you'd like to add an opt-out option then I could do that. But I kinda think that should be some added complexity that we should add only if necessary since this doesn't seem to be much of a problem.

[kentcdodds]

Ping? 😅

[RyanZim]

Hey, sorry for the slowness here; didn't want to merge until I had spare time to publish a new version.

[kentcdodds]

No worries. I know life is busy 😅 Thanks for merging and releasing this!

[chillitom]

could comparing files sizes first and only reading/comparing if different give a small perf improvement?

[kentcdodds]

I expect it could, but it's it really worth the added complexity? For most cases it doesn't even take a full millisecond to just read and compare. It probably wouldn't make much of a difference...