Enhancement: Add defaults for TSESLint.RuleContext type parameters

[JoshuaKGoldberg]

Before You File a Proposal Please Confirm You Have Done The Following...

• I have searched for related issues and found none that match my proposal.
• I have searched the current rule list and found no rules that match my proposal.
• I have read the FAQ and my problem is not listed.

Relevant Package

utils

My proposal is suitable for this project

• I believe my proposal would be useful to the broader TypeScript community (meaning it is not a niche proposal).

Description

Right now, RuleContext doesn't provide defaults for its type parameters:

typescript-eslint/packages/utils/src/ts-eslint/Rule.ts

Lines 175 to 178 in 99a026f

	interface RuleContext<
	TMessageIds extends string,
	TOptions extends readonly unknown[],
	> {

That means if you want to describe any arbitrary rule context the way e.g. #8146 does, you have to explicitly type out RuleContext<string, unknown[]>. It's a little inconvenient.

Proposal: let's add defaults to make referring to an "unknown" rule context a little easier?

interface RuleContext<
  TMessageIds extends string = string,
  TOptions extends readonly unknown[] = unknown[],
> {

Additional Info

#8148 is a draft PR showing the changes internally.

[bradzacher]

I think it's fine to not provide defaults because it means that you have to specifically opt-in to the unbounded, unsafe behaviour.

This is good because it means that if someone is writing a rule and wants to pass the context around they have to pass the parameters - preventing unsafe code.

For example this is a very common pattern I've seen:

const someUtil = (context: RuleContext<MessageIds, Options>) => { ... };

const rule = createRule<MessageIds, Options>({
  // ...
  create(context) {
    someUtil(context);
  },
});

You might say "but if they move the function into the create body they could remove the param entirely!" and you're not wrong - but who are we to dictate others preferred style?

If we default the type params then it's valid for the user to define context: RuleContext for said function - which means that when that function calls eg contex.report it will have zero safety around the message ids!

I'd much rather export an obviously unsafe version of the type like we do for the RuleModule

typescript-eslint/packages/utils/src/ts-eslint/Rule.ts

Line 636 in 99a026f

type AnyRuleModule = RuleModule<string, readonly unknown[]>;

[JoshuaKGoldberg]

Makes sense to me! Closing as wontfix. Thanks!