feat(eslint-plugin): add extension rule [no-invalid-this] too support arrow function class properties

[ghost]

Fixes #1571

But does not fix #491

This PR clones the no-invalid-this rule from eslint and modifies it to allow ArrowFunctionExpressions within a Class to reference this. I originally attempted to extend the base rule, but found I needed to be able modify what was being pushed to the stack variable which was inaccessible.

I realize this does not cover cases like:

class A {
    private foo = 0;
    constructor(number) {
        this.foo = number;
    }
    function increment() {
        this.foo += 1;
    }
}

but I'm not really sure how to navigate the AST to find what variables have been initialized in the constructor or on the class body. This is my first time working with ASTs, linters or parsers, so some guidance would really be appreciated!

[typescript-eslint]

Thanks for the PR, @sean-allen!

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!

---

🙏 Please, if you or your company is finding typescript-eslint valuable, help us sustain the project by sponsoring it transparently on https://opencollective.com/typescript-eslint. As a thank you, your profile/company logo will be added to our main README which receives thousands of unique visitors per day.

[codecov]

Codecov Report

Merging #1794 into master will decrease coverage by 0.02%.
The diff coverage is 88.46%.

@@            Coverage Diff             @@
##           master    #1794      +/-   ##
==========================================
- Coverage   94.48%   94.46%   -0.03%     
==========================================
  Files         162      163       +1     
  Lines        7490     7516      +26     
  Branches     2148     2153       +5     
==========================================
+ Hits         7077     7100      +23     
  Misses        178      178              
- Partials      235      238       +3     

Flag	Coverage Δ
#unittest	94.46% <88.46%> (-0.03%)	⬇️

Impacted Files	Coverage Δ
...ackages/eslint-plugin/src/rules/no-invalid-this.ts	88.46% <88.46%> (ø)

[bradzacher]

OOC, How come you even want to use this rule? Typescript does this check in various forms already.

It seems pretty redundant to use this rule.

[bradzacher]

Logic LGTM.
A few comments.
Please add documentation as per comment.

There were some lint changes recently that are firing on your tests, please address them.

Thanks for your work!

[bradzacher]

Mark the rule as an extension rule.
You'll have to regen the configs and docs after this change.

Suggested change

	recommended: false,
	recommended: false,
	extendsBaseRule: true,

[bradzacher]

it looks like you're not actually using baseRule inside this rule because you had to fork the logic.
In this case we should locally define the types and the schema.

We don't want to reference the parent rule's schema here because if they add a new option, we won't have handling for it until we add it to our fork.

Locally define the Options/MessageIds to match as well - we don't need the separate module type declarations.

[bradzacher]

nit

Suggested change

	const stack: CheckingContext[] = [],
	sourceCode = context.getSourceCode();
	const stack: CheckingContext[] = [];
	const sourceCode = context.getSourceCode();

[bradzacher]

Example of an extension rule doc:

https://github.com/typescript-eslint/typescript-eslint/blob/1fd86befa6a940a0354c619dd2da08a5c5d69fb4/packages/eslint-plugin/docs/rules/comma-spacing.md

Key points:

• explain what we've added
• show how to turn it on
• link to the base rule docs.

[bradzacher]

closing in favour of #1823