Only enable shadow lookup if shadowLookup experiment is enabled

__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)
   })

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 => {