allow for nested addVariant shorthand

This will allow to write something like:

```js
addVariant('name', `
  @supports (hover: hover) {
    @media (print) {
      &:hover
    }
  }
`)
// Or as a one-liner
addVariant('name', '@supports (hover: hover) { @media (print) { &:hover } }')
```

src/lib/setupContextUtils.js

@@ -19,6 +19,35 @@ import { toPath } from '../util/toPath'
 import log from '../util/log'
 import negateValue from '../util/negateValue'
 
+function parseVariantFormatString(input) {
+  if (input.includes('{')) {
+    if (!isBalanced(input)) throw new Error(`Your { and } are unbalanced.`)
+
+    return input
+      .split(/{(.*)}/gim)
+      .flatMap((line) => parseVariantFormatString(line))
+      .filter(Boolean)
+  }
+
+  return [input.trim()]
+}
+
+function isBalanced(input) {
+  let count = 0
+
+  for (let char of input) {
+    if (char === '{') {
+      count++
+    } else if (char === '}') {
+      if (--count < 0) {
+        return false // unbalanced
+      }
+    }
+  }
+
+  return count === 0
+}
+
 function insertInto(list, value, { before = [] } = {}) {
   before = [].concat(before)
 
@@ -191,12 +220,27 @@ function buildPluginApi(tailwindConfig, context, { variantList, variantMap, offs
           return variantFunction
         }
 
-        if (!variantFunction.startsWith('@')) {
-          return ({ format }) => format(variantFunction)
-        }
+        variantFunction = variantFunction
+          .replace(/\n+/g, '')
+          .replace(/\s{1,}/g, ' ')
+          .trim()
+
+        let fns = parseVariantFormatString(variantFunction)
+          .map((str) => {
+            if (!str.startsWith('@')) {
+              return ({ format }) => format(str)
+            }
+
+            let [, name, params] = /@(.*?) (\(.*\))/g.exec(str)
+            return ({ wrap }) => wrap(postcss.atRule({ name, params }))
+          })
+          .reverse()
 
-        let [, name, params] = /@(.*?) (\(.*\))/g.exec(variantFunction)
-        return ({ wrap }) => wrap(postcss.atRule({ name, params }))
+        return (api) => {
+          for (let fn of fns) {
+            fn(api)
+          }
+        }
       })
 
       insertInto(variantList, variantName, options)

tests/variants.test.js

@@ -244,3 +244,30 @@ it('should properly handle keyframes with multiple variants', async () => {
     }
   `)
 })
+
+test('custom addVariant with nested media & format shorthand', () => {
+  let config = {
+    content: [
+      {
+        raw: html` <div class="magic:text-center"></div> `,
+      },
+    ],
+    plugins: [
+      function ({ addVariant }) {
+        addVariant('magic', '@supports (hover: hover) { @media (print) { &:disabled } }')
+      },
+    ],
+  }
+
+  return run('@tailwind components;@tailwind utilities', config).then((result) => {
+    return expect(result.css).toMatchFormattedCss(css`
+      @supports (hover: hover) {
+        @media (print) {
+          .magic\\:text-center:disabled {
+            text-align: center;
+          }
+        }
+      }
+    `)
+  })
+})