Note added by @j-f1:

This is NOT the current plan for Prettier v2.0. We’ve significantly scaled back our plans for what Prettier 2.0 will do, allowing us to get a less-controversial release out sooner: #6888

I've been thinking a bit about what we would do if (don't create a milestone just yet 😉) we were to do a Prettier 2.0 release with some API/CLI breaking changes. No significant changes to code formatting other than perhaps changing some defaults.

Easy?

• Enforce Trailing Commas by Default #68/Can we enable the dangling comma on this project? #3469 - Change default value for trailingComma to "es5".
  The diff advantages alone are excellent, and this seems to be commonplace among the most popular JS projects.

CLI:

• config file doesn't work at the way other libraries do #2691 - CLI defaults to "**/*.{js,ts,...}".
  People should just be able to do prettier --write without passing messy globs #0CJS

• Consider replacing the "parser" option with "language" #2846 - Replace the "parser" option with "language".
  e.g. echo ".foo {}" | prettier --language css
  Keep --parser flow or perhaps support something like --parser.js flow for future extensibility.

• Remove --flow-parser option.
  Has been deprecated for a long time.

For debate

• Consistently add quotes to object keys #838 - Consistently add quotes to object keys.
  e.g. put quotes around origin in this example:

  const headers = {
    'origin': 'foo.com',
    'access-control-allow-origin': '*',
  };

• Change the default value for singleQuote to true

  • Airbnb, standard, xo, and probably the majority of JS devs prefer this. Maybe do a Twitter poll to gauge opinions on this.

To be clear, the Airbnb config requires single quotes for JS and double quotes for JSX.

Outdated

• Consider removing default parser / Skip processing unsupported file types #2884 - Remove the default parser. Fixed by Don't default parser to babylon #4528

• Space after function keyword - MOVED to #3847! #1139 - Put a space after the n in function () {}