Accept immutable arrays within fromFixture

[rafaelss95]

Consider this scenario:

type MessageIds = ESLintUtils.InferMessageIdsTypeFromRule<typeof rule> // 'preferConcatLatestFrom'
type Options = ESLintUtils.InferOptionsTypeFromRule<typeof rule> // [{ readonly strict: boolean; }]

const valid: TSESLint.RunTests<MessageIds, Options>['valid'] = []
const invalid: TSESLint.RunTests<MessageIds, Options>['invalid'] = [
  fromFixture(``, {
    options: [{ strict: true }], // here I get the error described below
    output: ``,
  }),
]

Type 'InvalidTestCase<"preferConcatLatestFrom", { strict: boolean; }[]>' is not assignable to type 'InvalidTestCase<"preferConcatLatestFrom", Options>'.
Types of property 'options' are incompatible.
Type 'readonly { strict: boolean; }[]' is not assignable to type 'readonly [{ strict: boolean; }]'.
Target requires 1 element(s) but source may have fewer.ts(2322)

So, to fix this, I can either do options: [{ strict: true }] as const or { output: ..., options: ... } as const and so the TS is happy, however fromFixture doesn't accept readonly arrays...

I believe that it's a simple change:

- export declare function fromFixture<TMessageIds extends string, TOptions extends unknown[]>
+ export declare function fromFixture<TMessageIds extends string, TOptions extends readonly unknown[]>

and

- suggestions?: eslint.SuggestionOutput<string>[] | null | undefined;
+ suggestions?: readonly eslint.SuggestionOutput<string>[] | null | undefined;
- suggestions?: eslint.SuggestionOutput<TMessageIds>[] | null | undefined;
+ suggestions?: readonly eslint.SuggestionOutput<TMessageIds>[] | null | undefined;

Let me know if this case was clear enough to describe the issue (and I'm able to help submitting a PR if that's the case).

[cartant]

Let me know if this case was clear enough to describe the issue (and I'm able to help submitting a PR if that's the case).

Sure. Open a PR if you have time.

[cartant]

Closed by #6 and published as 4.2.6.