feat(experimental-utils): allow rule options to be a readonly tuple

[ulrichb]

• Change createRule's TOptions to a readonly generic constraint ...
• ... and make it mutable exactly where it's necessary: within applyDefault() (after cloning it, the mutation happens in line 26 & 28)

=> This allows to create a rule this way:

ESLintUtils.RuleCreator(name => name)<readonly [{ readonly prop: string }],
    "defaultMessage">({
    name: "name", meta: { /* ... */ },
    create(context, options) {

        // This is now a compile error ("Cannot assign to '0' because it
        //  is a read-only property"), which is gooodd:
        options[0] = { prop: "x" };

        return {};
    },
});

[typescript-eslint]

Thanks for the PR, @ulrichb!

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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[codecov]

Codecov Report

Merging #1924 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1924   +/-   ##
=======================================
  Coverage   94.36%   94.36%           
=======================================
  Files         166      166           
  Lines        7608     7608           
  Branches     2185     2185           
=======================================
  Hits         7179     7179           
  Misses        183      183           
  Partials      246      246           

Flag	Coverage Δ
#unittest	94.36% <100.00%> (ø)

Impacted Files	Coverage Δ
...experimental-utils/src/eslint-utils/RuleCreator.ts	66.66% <ø> (ø)
...xperimental-utils/src/eslint-utils/applyDefault.ts	100.00% <100.00%> (ø)

[bradzacher]

Thanks! I've been wanting to get in and do this for a while

[ulrichb]

Thanks! I've been wanting to get in and do this for a while

:)

Thanks for merging!