Ensure comments in @layer rules don't crash

CHANGELOG.md

@@ -31,6 +31,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix before/after utilities overriding custom content values at larger breakpoints ([#5820](https://github.com/tailwindlabs/tailwindcss/pull/5820))
 - Cleanup duplicate properties ([#5830](https://github.com/tailwindlabs/tailwindcss/pull/5830))
 - Allow `_` inside `url()` when using arbitrary values ([#5853](https://github.com/tailwindlabs/tailwindcss/pull/5853))
+- Prevent crashes when using comments in `@layer` AtRules ([#5854](https://github.com/tailwindlabs/tailwindcss/pull/5854))
 
 ## [3.0.0-alpha.1] - 2021-10-01
 

src/lib/generateRules.js

@@ -448,28 +448,42 @@ function generateRules(candidates, context) {
     allRules.push(matches)
   }
 
-  return allRules.flat(1).map(([{ sort, layer, options }, rule]) => {
-    if (options.respectImportant) {
-      if (context.tailwindConfig.important === true) {
+  // Strategy based on `tailwindConfig.important`
+  let strategy = ((important) => {
+    if (important === true) {
+      return (rule) => {
         rule.walkDecls((d) => {
           if (d.parent.type === 'rule' && !inKeyframes(d.parent)) {
             d.important = true
           }
         })
-      } else if (typeof context.tailwindConfig.important === 'string') {
+      }
+    }
+
+    if (typeof important === 'string') {
+      return (rule) => {
+        rule.selectors = rule.selectors.map((selector) => {
+          return `${important} ${selector}`
+        })
+      }
+    }
+  })(context.tailwindConfig.important)
+
+  return allRules.flat(1).map(([{ sort, layer, options }, rule]) => {
+    if (options.respectImportant) {
+      if (strategy) {
         let container = postcss.root({ nodes: [rule.clone()] })
         container.walkRules((r) => {
           if (inKeyframes(r)) {
             return
           }
 
-          r.selectors = r.selectors.map((selector) => {
-            return `${context.tailwindConfig.important} ${selector}`
-          })
+          strategy(r)
         })
         rule = container.nodes[0]
       }
     }
+
     return [sort | context.layerOrder[layer], rule]
   })
 }

tests/layer-at-rules.test.js

@@ -50,6 +50,125 @@ test('custom user-land utilities', () => {
   })
 })
 
+test('comments can be used inside layers without crashing', () => {
+  let config = {
+    content: [
+      {
+        raw: html`<div class="important-utility important-component"></div>`,
+      },
+    ],
+    corePlugins: { preflight: false },
+    theme: {},
+    plugins: [],
+  }
+
+  let input = css`
+    @tailwind base;
+    @tailwind components;
+    @tailwind utilities;
+
+    @layer base {
+      /* Important base */
+      div {
+        background-color: #bada55;
+      }
+    }
+
+    @layer utilities {
+      /* Important utility */
+      .important-utility {
+        text-align: banana;
+      }
+    }
+
+    @layer components {
+      /* Important component */
+      .important-component {
+        text-align: banana;
+      }
+    }
+  `
+
+  return run(input, config).then((result) => {
+    expect(result.css).toMatchFormattedCss(css`
+      /* Important base */
+      div {
+        background-color: #bada55;
+      }
+
+      /* Important component */
+      .important-component {
+        text-align: banana;
+      }
+
+      /* Important utility */
+      .important-utility {
+        text-align: banana;
+      }
+    `)
+  })
+})
+
+test('comments can be used inside layers (with important) without crashing', () => {
+  let config = {
+    important: true,
+    content: [
+      {
+        raw: html`<div class="important-utility important-component"></div>`,
+      },
+    ],
+    corePlugins: { preflight: false },
+    theme: {},
+    plugins: [],
+  }
+
+  let input = css`
+    @tailwind base;
+    @tailwind components;
+    @tailwind utilities;
+
+    @layer base {
+      /* Important base */
+      div {
+        background-color: #bada55;
+      }
+    }
+
+    @layer utilities {
+      /* Important utility */
+      .important-utility {
+        text-align: banana;
+      }
+    }
+
+    @layer components {
+      /* Important component */
+      .important-component {
+        text-align: banana;
+      }
+    }
+  `
+
+  return run(input, config).then((result) => {
+    expect(result.css).toMatchFormattedCss(css`
+      /* Important base */
+      div {
+        background-color: #bada55;
+      }
+
+      /* Important component */
+      .important-component {
+        text-align: banana;
+      }
+
+      /* Important utility */
+      .important-utility {
+        text-align: banana !important;
+      }
+    `)
+  })
+})
+
 test('layers are grouped and inserted at the matching @tailwind rule', () => {
   let config = {
     content: [