Add support for making applied rules important

__tests__/applyAtRule.test.js

@@ -14,11 +14,36 @@ test("it copies a class's declarations into itself", () => {
   })
 })
 
-test('it removes important from applied classes', () => {
-  const output = '.a { color: red !important; } .b { color: red; }'
+test('it removes important from applied classes by default', () => {
+  const input = `
+    .a { color: red !important; }
+    .b { @apply .a; }
+  `
 
-  return run('.a { color: red !important; } .b { @apply .a; }').then(result => {
-    expect(result.css).toEqual(output)
+  const expected = `
+    .a { color: red !important; }
+    .b { color: red; }
+  `
+
+  return run(input).then(result => {
+    expect(result.css).toEqual(expected)
+    expect(result.warnings().length).toBe(0)
+  })
+})
+
+test('applied rules can be made !important', () => {
+  const input = `
+    .a { color: red; }
+    .b { @apply .a !important; }
+  `
+
+  const expected = `
+    .a { color: red; }
+    .b { color: red !important; }
+  `
+
+  return run(input).then(result => {
+    expect(result.css).toEqual(expected)
     expect(result.warnings().length).toBe(0)
   })
 })

src/lib/substituteClassApplyAtRules.js

@@ -2,10 +2,8 @@ import _ from 'lodash'
 import postcss from 'postcss'
 import escapeClassName from '../util/escapeClassName'
 
-function normalizeClassNames(classNames) {
-  return classNames.map(className => {
-    return `.${escapeClassName(_.trimStart(className, '.'))}`
-  })
+function normalizeClassName(className) {
+  return `.${escapeClassName(_.trimStart(className, '.'))}`
 }
 
 function findMixin(css, mixin, onError) {
@@ -52,14 +50,17 @@ export default function() {
           return _.startsWith(mixin, '--')
         })
 
-        const decls = _.flatMap(normalizeClassNames(classes), mixin => {
-          return findMixin(css, mixin, message => {
-            throw atRule.error(message)
+        const decls = _(classes)
+          .reject(mixin => mixin === '!important')
+          .flatMap(mixin => {
+            return findMixin(css, normalizeClassName(mixin), message => {
+              throw atRule.error(message)
+            })
           })
-        })
+          .value()
 
-        decls.forEach(decl => {
-          decl.important = false
+        _.tap(_.last(mixins) === '!important', important => {
+          decls.forEach(decl => (decl.important = important))
         })
 
         atRule.before(decls)