New: ability to only lint for certain parts of the code block

Ref https://github.com/airbnb/javascript/issues/685

Not sure how this would work but an example would be in airbnb’s style guide.

3.1 Use the literal syntax for object creation. eslint rules: no-new-object.

// bad
const item = new Object();

// good
const item = {};

So in this case you would want to check the // good part is linted correctly while the // bad snippet is incorrect.

[btmills]

I just added HTML comments preceding code blocks in the ESLint rule docs, and our new renderer is preserving the comments correctly! I also ran a test with the parser in this plugin. As long as there’s still a blank line preceding the code block (this is required by spec anyway), it correctly picks up the raw HTML and the code block separately.

• <!--eslint-plugin-markdown ignore-->
• <!--eslint-disable-block-->
• <!--eslint-disable--> / <!--eslint-enable-->
• <!--eslint-plugin-markdown-disable--> / <!--eslint-plugin-markdown-enable-->

Brainstorming a few different options there. Any preferences/other ideas?

[btmills]

Below, I’ve borrowed from ESLint’s eqeqeq docs and inserted comments to demonstrate what this should look like given the latest proposal. Any objections to implementing this as described?

When disabling a specific rule <!--eslint-disable-next-block eqeqeq-->, the plugin will alert for syntax errors and other rules but ignore errors from eqeqeq:

### always

The `"always"` option (default) enforces the use of `===` and `!==` in every situation.

Examples of **incorrect** code for the `"always"` option:

<!--eslint-disable-next-block eqeqeq-->

```js
/*eslint eqeqeq: ["error", "always"]*/

a == b
foo == true
bananas != 1
```

Without any comments, the plugin will report all errors as received from ESLint:

Examples of **correct** code for the `"always"` option:

```js
/*eslint eqeqeq: ["error", "always"]*/

a === b
foo === true
bananas !== 1
```

When disabled for the entire block, the plugin won’t even bother sending the code to ESLint:

Examples of **syntax errors**:

<!--eslint-disable-next-block-->

```js
!@#$%^&*()
```