stylelint-at-rule-no-children

Stylelint rule to disallow block declarations inside at rules.

Usage
Configuration
Why?
TL;DR

Usage

Install the package:
npm i stylelint-at-rule-no-children
Add the plugin and rule to your .stylelintrc, like so:

{
  ...
  plugins: [
    ...
    "stylelint-at-rule-no-children",
  ],
  rules: {
    ...
    "adityavm/at-rule-no-children": [{ <options> }],
  }
}

Configuration

The rule accepts an ignore list of strings to allow when checking rules or their parameters. Consider the following:

@include foo() {
  body { color: #ff0000; }
}

@foo() {
  body { color: #ff0000; }
}

Normally, both the above blocks would be rejected. However, setting the following config will allow them both:

{
  "adityavm/stylelint-at-rule-no-children": [{ ignore: ["foo"] }],
}

Note: This is not recommended, as it goes against the ideology behind the plugin. But if you need to define exceptions, now you can.

Why?

Conceptually, this is similar to why we don't declare functions inside conditional blocks in general programming.
CSS is inherently difficult to understand after a certain point. When we introduce branches in the CSS, it becomes more difficult. To top off the complexity, CSS allows defining whole blocks inside a conditional block, which can result in multiple declarations of the same selectors in different parts of the file (especially if more than one developer touches a file).
By disallowing block declarations inside at rules, we force developers to have only one declaration for a selector per file. Any and all conditions are included in that selector. This ensures that a developer searching through a file for a selector can be sure that their first hit is the only declaration they need to consider.

TL;DR

/* good css */

.foo {
  color: red;

  @media screen and (max-width: 480px) {
    color: blue;
  }
}

/* bad css */

.foo {
  color: red;
}

@media screen and (max-width: 480px) {
  .foo {
    color: blue;
  }
}