What rule do you want to change?

comma-dangle

Does this change cause the rule to produce more or fewer warnings?

That depends.

How will the change be implemented? (New option, new default behavior, etc.)?

This is a feature request from Node.js: it would be nice to add a consistent option to comma-dangle that checks if the whole file has a consistent style of either always having trailing commas or having no trailing commas at all. With the current options something like this is not possible.

Refs: nodejs/node#20703 (comment)

Please provide some example code that this change will affect:

const a = [
  1,
  2,
]

const b = [
  1,
  2
]

const a = {
  a: 1,
  b: 2,
}

const b = {
  a: 1,
  b: 2
}

What does the rule currently do for this code?

Using the only-multiline option results in no error. Using the always-multiline always reports errors.

What will the rule do after it's changed?

It should report an issue as long as both styles are used in a single file. If the file has either a consistent trailing comma style or no trailing commas, it should not report an issue.