Please describe what the rule should do:

If an accessor property has both getter and setter functions, this rule requires their definitions to be one after another in object literals/class definitions.

Optionally, the rule can require their order (get before set, or set before get).

What category of rule is this? (place an "X" next to just one item)

[X] Enforces code style (layout)

Provide 2-3 code examples that this rule will warn about:

/* eslint compact-accessor:error*/
var foo = {
    get a(){},
    bar: 5,
    set a(val){}
};

var foo = {
    get a(){},
    ...bar,
    set a(val){}
}

class foo {
    get a(){}
    bar(){}
    set a(val){}
}

/* eslint compact-accessor:["error", "getBeforeSet"]*/
var foo = {
    set a(val){},
    get a(){}
}

class foo {
    set a(val){}
    get a(){}
}

Why should this rule be included in ESLint (instead of a plugin)?

While it is allowed, I don't think there is a real use case for non-consecutive definitions of accessor functions for the same property, and it should be a best practice to avoid this feature. Also, the additional option can enforce a consistent style (e.g., get before set).

I'm not sure about the rule's name, there could be a better word than compact for this.

Notes:

• The rule does not enforce the existence of the pair for a getter/setter (that's accessor-pairs).
• The rule does not require grouping of all accessor properties at the same place, it works with each individually.
• If a property has a duplicate getter or setter, such property will be ignored by this rule and caught by other rules (no-dupe-keys and no-dupe-class-members)

Problem: This rule is overlapping with sort-keys. But, one might want to enforce this without sorting. Also, sort-keys doesn't work with classes and doesn't enforce get/set order.

Are you willing to submit a pull request to implement this rule?

Yes.