Escape class names provided in @apply

Without this, can't mixin stuff like .w-1/4.

src/lib/substituteClassApplyAtRules.js

@@ -1,13 +1,27 @@
 import postcss from 'postcss'
 import _ from 'lodash'
 import findMixin from '../util/findMixin'
+import escapeClassName from '../util/escapeClassName'
+
+function normalizeClassNames(classNames) {
+  return classNames.map((className) => {
+    return `.${escapeClassName(_.trimStart(className, '.'))}`
+  })
+}
 
 export default postcss.plugin('tailwind-apply', function(css) {
   return function(css) {
     css.walkRules(function(rule) {
       rule.walkAtRules('apply', atRule => {
-        const mixins = postcss.list.space(atRule.params)
+        const mixins = normalizeClassNames(postcss.list.space(atRule.params))
 
+        /*
+         * Don't wreck CSSNext-style @apply rules:
+         * http://cssnext.io/features/#custom-properties-set-apply
+         *
+         * These are deprecated in CSSNext but still playing it safe for now.
+         * We might consider renaming this at-rule.
+         */
         const [customProperties, classes] = _.partition(mixins, mixin => {
           return _.startsWith(mixin, '--')
         })

src/util/defineClass.js

@@ -1,9 +1,6 @@
 import _ from 'lodash'
 import postcss from 'postcss'
-
-function escapeSelector(selector) {
-    return selector.replace(/([^A-Za-z0-9\-])/g, "\\$1")
-}
+import escapeClassName from './escapeClassName'
 
 export default function(className, properties) {
   const decls = _.map(properties, (value, property) => {
@@ -14,6 +11,6 @@ export default function(className, properties) {
   })
 
   return postcss.rule({
-    selector: `.${escapeSelector(className)}`,
+    selector: `.${escapeClassName(className)}`,
   }).append(decls)
 }

src/util/escapeClassName.js

@@ -0,0 +1,3 @@
+export default function escapeClassName(className) {
+    return className.replace(/([^A-Za-z0-9\-])/g, "\\$1")
+}