use known tree to handle @apply when required @tailwind at rules …

…exists

Otherwise we will generate the lookup tree.

__tests__/applyAtRule.test.js

@@ -337,16 +337,16 @@ test('you can apply utility classes that do not actually exist as long as they w
   })
 })
 
-test('the shadow lookup is only used if no @tailwind rules were in the source tree', () => {
+test('shadow lookup will be constructed when we have missing @tailwind atrules', () => {
   const input = `
     @tailwind base;
     .foo { @apply mt-4; }
   `
 
   expect.assertions(1)
 
-  return run(input).catch((e) => {
-    expect(e).toMatchObject({ name: 'CssSyntaxError' })
+  return run(input).then((result) => {
+    expect(result.css).toContain(`.foo { margin-top: 1rem;\n}`)
   })
 })
 

src/lib/substituteClassApplyAtRules.js

@@ -310,7 +310,15 @@ export default function substituteClassApplyAtRules(config, getProcessedPlugins,
     }
 
     // Tree already contains @tailwind rules, don't prepend default Tailwind tree
-    if (hasAtRule(css, 'tailwind')) {
+    let requiredTailwindAtRules = ['utilities']
+    if (
+      hasAtRule(css, 'tailwind', (node) => {
+        let idx = requiredTailwindAtRules.indexOf(node.params)
+        if (idx !== -1) requiredTailwindAtRules.splice(idx, 1)
+        if (requiredTailwindAtRules.length <= 0) return true
+        return false
+      })
+    ) {
       return processApplyAtRules(css, postcss.root(), config)
     }