From 24e1385aca46dba4cfb3d0cbabce023a0374c37a Mon Sep 17 00:00:00 2001
From: Adam Wathan <adam.wathan@gmail.com>
Date: Wed, 11 Jul 2018 11:51:47 -0400
Subject: [PATCH] Only enable shadow lookup if shadowLookup experiment is
 enabled

---
 __tests__/applyAtRule.test.js          | 7 ++++++-
 src/lib/substituteClassApplyAtRules.js | 4 +++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/__tests__/applyAtRule.test.js b/__tests__/applyAtRule.test.js
index 18c739314..873fc8678 100644
--- a/__tests__/applyAtRule.test.js
+++ b/__tests__/applyAtRule.test.js
@@ -202,7 +202,12 @@ test('you can apply utility classes that do not actually exist as long as they w
     .foo { margin-top: 1rem; }
   `
 
-  return run(input).then(result => {
+  const config = {
+    ...defaultConfig,
+    experiments: { shadowLookup: true },
+  }
+
+  return run(input, config).then(result => {
     expect(result.css).toEqual(expected)
     expect(result.warnings().length).toBe(0)
   })
diff --git a/src/lib/substituteClassApplyAtRules.js b/src/lib/substituteClassApplyAtRules.js
index 2848f231e..01dfb3c28 100644
--- a/src/lib/substituteClassApplyAtRules.js
+++ b/src/lib/substituteClassApplyAtRules.js
@@ -59,7 +59,9 @@ function findClass(classToApply, classTable, shadowLookup, onError) {
 export default function(config, generatedUtilities) {
   return function(css) {
     const classLookup = buildClassTable(css)
-    const shadowLookup = buildShadowTable(generatedUtilities)
+    const shadowLookup = _.get(config, 'experiments.shadowLookup', false)
+      ? buildShadowTable(generatedUtilities)
+      : {}
 
     css.walkRules(rule => {
       rule.walkAtRules('apply', atRule => {