prevent rules inside media queries from being used as a mixin

__tests__/applyAtRule.test.js

@@ -0,0 +1,54 @@
+var postcss = require('postcss')
+
+import plugin from '../src/lib/substituteClassApplyAtRules'
+
+function run(input, opts) {
+    return postcss([plugin(opts)]).process(input)
+}
+
+test("it copies a class's declarations into itself", () => {
+    const output = '.a { color: red; } .b { color: red; }'
+
+    return run('.a { color: red; } .b { @apply .a; }', {}).then(result => {
+        expect(result.css).toEqual(output)
+        expect(result.warnings().length).toBe(0)
+    })
+})
+
+test("it doesn't copy a media query definition into itself", () => {
+    const output = `.a {
+            color: red;
+        }
+
+        @media (min-width: 300px) {
+            .a { color: blue; }
+        }
+
+        .b {
+            color: red;
+        }`
+
+    return run(
+        `.a {
+            color: red;
+        }
+
+        @media (min-width: 300px) {
+            .a { color: blue; }
+        }
+
+        .b {
+            @apply .a;
+        }`,
+        {}
+    ).then(result => {
+        expect(result.css).toEqual(output)
+        expect(result.warnings().length).toBe(0)
+    })
+})
+
+test('it fails if the class does not exist', () => {
+    run('.b { @apply .a; }', {}).catch(error => {
+        expect(error.reason).toEqual('No .a class found.')
+    })
+})

src/util/findMixin.js

@@ -4,7 +4,7 @@ export default function findMixin(css, mixin, onError) {
   const matches = []
 
   css.walkRules(rule => {
-    if (rule.selectors.includes(mixin)) {
+    if (rule.selectors.includes(mixin) && rule.parent.type == 'root') {
       matches.push(rule)
     }
   })