fix(eslint-plugin): [no-unnecessary-condition] fix false positive for type variable

[yeonjuan]

PR Checklist

• Addresses an existing open issue: fixes Bug: [no-unnecessary-condition] false positive on indexed access of a generic type #7850
• That issue was marked as accepting prs
• Steps in Contributing were taken

Overview

Fix the following false positive cases.

• demo

function foo<T extends object>(
  arg: T,
  key: keyof T
): void {
  const t1 = arg[key] == null;
  const t2 = null == arg[key];
  const t3 = arg[key] != null;
  const t4 = null != arg[key];
  const t5 = arg[key] == undefined;
  const t6 = undefined == arg[key];
  const t7 = arg[key] != undefined;
  const t8 = undefined != arg[key];
  const t9 = arg[key] === null;
  const t10 = null === arg[key];
  const t11 = arg[key] !== null;
  const t12 = null !== arg[key];
  const t13 = arg[key] === undefined;
  const t14 = undefined === arg[key];
  const t15 = arg[key] !== undefined;
  const t16 = undefined !== arg[key];
  arg[key] ?? 'default';
  arg[key] ??= 'default';
  arg[key] ||= 'default';
}

[typescript-eslint]

Thanks for the PR, @yeonjuan!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[JoshuaKGoldberg]

This looks great to me, thanks for the fix!

Just one note on testing, but I'm happy to merge as-is or make the cleanup myself given that the tests for this rule already do the "test a lot in one case" thing.

[yeonjuan]

Suggested change

	function foo<T extends object>(arg: T, key: keyof T): void {
	const t1 = arg[key] == null;
	const t2 = null == arg[key];
	const t3 = arg[key] != null;
	const t4 = null != arg[key];
	const t5 = arg[key] == undefined;
	const t6 = undefined == arg[key];
	const t7 = arg[key] != undefined;
	const t8 = undefined != arg[key];
	const t9 = arg[key] === null;
	const t10 = null === arg[key];
	const t11 = arg[key] !== null;
	const t12 = null !== arg[key];
	const t13 = arg[key] === undefined;
	const t14 = undefined === arg[key];
	const t15 = arg[key] !== undefined;
	const t16 = undefined !== arg[key];
	}
	function foo<T extends object>(arg: T, key: keyof T): void {
	arg[key] == null;
	}

[yeonjuan]

Suggested change

	function foo<T extends object>(arg: T, key: keyof T): void {
	arg[key] ??= 'default';
	arg[key] ||= 'default';
	arg[key] &&= 'default';
	function foo<T extends object>(arg: T, key: keyof T): void {
	arg[key] ??= 'default';

[JoshuaKGoldberg]

💯 looks great, thanks as always!