Typescript-eslint: Rule proposal: prefer hash names for private members

[kimamula]

TypeScript 3.8 will add support for private named instance fields. What about creating a rule for disallowing the use of the private accessibility modifier in favor of the standard hash names for private members?

Examples of incorrect code for this rule:

class MyClass {
  private foo = 1;
  constructor(private bar: string) {}
}

Examples of correct code for this rule:

class MyClass {
  #foo = 1;
  #bar: string;
  constructor(bar: string) {
    this.#bar = bar;
  }
}

Options

// Any target whose hash names are supported
// by the TypeScript version in use can be specified
type Target =
//  | 'accessors'
//  | 'constructors'
//  | 'staticMethods'
//  | 'instanceMethods'
//  | 'staticFields'
  | 'instanceFields';

type Options = Target[];

// Defaults to all the targets
const defaultOptions: Options = ['instanceFields']; // for TypeScript 3.8

[glen-84]

Perhaps it should allow the opposite as well – enforcing soft (compile-time-only) privacy?

[bradzacher]

Probably best to be added as an option on the explicit-member-accessibility rule.

[kimamula]

Then the options for explicit-member-accessibility should be changed to something like the following?

type AccessibilityLevel =
  | 'explicit' // require an accessor (including public)
  | 'no-public' // don't require public
  | 'off'; // don't check

type PrivateMemberDeclaration =
  | 'private' // force private modifier
  | '#' // force hash names
  | 'off'; // don't check, default

type AccessibilitySetting = AccessibilityLevel | [AccessibilityLevel, PrivateMemberDeclaration];

type Options = {
  accessibility?: AccessibilitySetting;
  ignoredMethodNames?: string[];
  overrides?: {
    accessors?: AccessibilitySetting;
    constructors?: AccessibilitySetting;
    methods?: AccessibilitySetting | {
      static?: AccessibilitySetting;
      instance?: AccessibilitySetting;
    };
    properties?: AccessibilitySetting | {
      static?: AccessibilitySetting;
      instance?: AccessibilitySetting;
    };
    parameterProperties?: AccessibilitySetting;
  };
};

const defaultOptions: Options = {
  accessibility: 'explicit',
};

I'm afraid that the name explicit-member-accessibility is a bit confusing for this use case though.
Perhaps it should be renamed to something like member-accessibility and the name explicit-member-accessibility should remain as an alias for it?