Prefix all classes in a selector, don't assume single class

__tests__/prefixTree.test.js

@@ -29,6 +29,7 @@ test('it handles a function as the prefix', () => {
   `
 
   const prefixFunc = selector => {
+    return selector === '.foo' ? 'tw-' : ''
     if (selector === '.foo') {
       return 'tw-'
     }
@@ -40,3 +41,17 @@ test('it handles a function as the prefix', () => {
   expect(result.css).toEqual(expected)
   expect(result.warnings().length).toBe(0)
 })
+
+test('it prefixes all classes in a selector', () => {
+  const input = postcss.parse(`
+    .btn-blue .w-1\\/4 > h1.text-xl + a .bar { color: red; }
+  `)
+
+  const expected = `
+    .tw-btn-blue .tw-w-1\\/4 > h1.tw-text-xl + a .tw-bar { color: red; }
+  `
+
+  const result = prefixTree(input, 'tw-').toResult()
+  expect(result.css).toEqual(expected)
+  expect(result.warnings().length).toBe(0)
+})

__tests__/processPlugins.test.js

@@ -755,3 +755,26 @@ test('variants can still be specified when ignoring prefix and important options
     }
   `)
 })
+
+test('prefix will prefix all classes in a selector', () => {
+  const [components] = processPluginsWithValidConfig({
+    plugins: [
+      function({ addComponents, prefix }) {
+        addComponents({
+          [prefix('.btn-blue .w-1\\/4 > h1.text-xl + a .bar')]: {
+            backgroundColor: 'blue',
+          },
+        })
+      },
+    ],
+    options: {
+      prefix: 'tw-',
+    },
+  })
+
+  expect(css(components)).toMatchCss(`
+    .tw-btn-blue .tw-w-1\\/4 > h1.tw-text-xl + a .tw-bar {
+      background-color: blue
+    }
+  `)
+})

package.json

@@ -50,7 +50,8 @@
     "postcss": "^6.0.9",
     "postcss-functions": "^3.0.0",
     "postcss-js": "^1.0.1",
-    "postcss-nested": "^3.0.0"
+    "postcss-nested": "^3.0.0",
+    "postcss-selector-parser": "^3.1.1"
   },
   "browserslist": [
     "> 1%"

src/util/prefixSelector.js

@@ -1,5 +1,11 @@
+import parser from 'postcss-selector-parser'
+
 export default function(prefix, selector) {
   const getPrefix = typeof prefix === 'function' ? prefix : () => prefix
 
-  return `.${getPrefix(selector)}${selector.slice(1)}`
+  return parser(selectors => {
+    selectors.walkClasses((classSelector) => {
+      classSelector.value = `${getPrefix('.' + classSelector.value)}${classSelector.value}`
+    })
+  }).processSync(selector)
 }