make sure nesting folder is available

.gitignore

@@ -10,11 +10,8 @@ index.html
 yarn.lock
 yarn-error.log
 
-# "External" plugins
-/nesting
-
 # Perf related files
 isolate*.log
 
 # Generated files
-/src/corePluginList.js
+/src/corePluginList.js

nesting/README.md

@@ -0,0 +1,42 @@
+# tailwindcss/nesting
+
+This is a PostCSS plugin that wraps [postcss-nested](https://github.com/postcss/postcss-nested) or [postcss-nesting](https://github.com/jonathantneal/postcss-nesting) and acts as a compatibility layer to make sure your nesting plugin of choice properly understands Tailwind's custom syntax like `@apply` and `@screen`.
+
+Add it to your PostCSS configuration, somewhere before Tailwind itself:
+
+```js
+// postcss.config.js
+module.exports = {
+  plugins: [
+    require('postcss-import'),
+    require('tailwindcss/nesting'),
+    require('tailwindcss'),
+    require('autoprefixer'),
+  ]
+}
+```
+
+By default, it uses the [postcss-nested](https://github.com/postcss/postcss-nested) plugin under the hood, which uses a Sass-like syntax and is the plugin that powers nesting support in the [Tailwind CSS plugin API](https://tailwindcss.com/docs/plugins#css-in-js-syntax).
+
+If you'd rather use [postcss-nesting](https://github.com/jonathantneal/postcss-nesting) (which is based on the work-in-progress [CSS Nesting](https://drafts.csswg.org/css-nesting-1/) specification), first install the plugin alongside:
+
+```shell
+npm install postcss-nesting
+```
+
+Then pass the plugin itself as an argument to `tailwindcss/nesting` in your PostCSS configuration:
+
+```js
+// postcss.config.js
+module.exports = {
+  plugins: [
+    require('postcss-import'),
+    require('tailwindcss/nesting')(require('postcss-nesting')),
+    require('tailwindcss'),
+    require('autoprefixer'),
+  ]
+}
+```
+
+This can also be helpful if for whatever reason you need to use a very specific version of `postcss-nested` and want to override the version we bundle with `tailwindcss/nesting` itself.
+

nesting/index.js

@@ -0,0 +1,12 @@
+let nesting = require('./plugin')
+
+module.exports = (opts) => {
+  return {
+    postcssPlugin: 'tailwindcss/nesting',
+    Once(root, { result }) {
+      return nesting(opts)(root, result)
+    },
+  }
+}
+
+module.exports.postcss = true

nesting/plugin.js

@@ -0,0 +1,41 @@
+let postcss = require('postcss')
+let postcssNested = require('postcss-nested')
+
+module.exports = function nesting(opts = postcssNested) {
+  return (root, result) => {
+    root.walkAtRules('screen', (rule) => {
+      rule.name = 'media'
+      rule.params = `screen(${rule.params})`
+    })
+
+    root.walkAtRules('apply', (rule) => {
+      rule.before(postcss.decl({ prop: '__apply', value: rule.params, source: rule.source }))
+      rule.remove()
+    })
+
+    let plugin = (() => {
+      if (typeof opts === 'function') {
+        return opts
+      }
+
+      if (typeof opts === 'string') {
+        return require(opts)
+      }
+
+      if (Object.keys(opts).length <= 0) {
+        return postcssNested
+      }
+
+      throw new Error('tailwindcss/nesting should be loaded with a nesting plugin.')
+    })()
+
+    postcss([plugin]).process(root, result.opts).sync()
+
+    root.walkDecls('__apply', (decl) => {
+      decl.before(postcss.atRule({ name: 'apply', params: decl.value, source: decl.source }))
+      decl.remove()
+    })
+
+    return root
+  }
+}