Fix: do not crash on @layer {} or other atrules without prelude (#357)

Reported on Twitter by @alexmacarthur
https://twitter.com/amacarthur/status/1719715202092982649

Author: bartveneman

src/atrules/atrules.test.js

@@ -71,6 +71,13 @@ AtRules('finds @layer', () => {
     @layer components {
       @layer defaults, structures, themes, utilities;
     }
+
+    /* Anonymous layer (no prelude/layer name) */
+    @layer {
+      test {
+        color: green;
+      }
+    }
   `
   const actual = analyze(fixture).atrules.layer
   const expected = {
@@ -241,6 +248,9 @@ AtRules('finds @imports', () => {
     @import url('../example.css') layer;
 
     @import url('remedy.css') layer(reset.remedy);
+
+    /* @import without prelude */
+    @import;
   `
   const actual = analyze(fixture).atrules.import
   const expected = {
@@ -265,6 +275,9 @@ AtRules('finds @charsets', () => {
   const fixture = `
     @charset "UTF-8";
     @charset "UTF-16";
+
+    /* No prelude */
+    @charset;
   `
   const actual = analyze(fixture).atrules.charset
   const expected = {
@@ -289,6 +302,9 @@ AtRules('finds @supports', () => {
     @media (min-width: 0) {
       @supports (-webkit-appearance: none) {}
     }
+
+    /* No prelude */
+    @supports {}
   `
   const actual = analyze(fixture).atrules.supports
 
@@ -353,6 +369,9 @@ AtRules('finds @media', () => {
     @supports (-webkit-appearance: none) {
       @media (min-width: 0) {}
     }
+
+    /* No prelude */
+    @media {}
   `
   const actual = analyze(fixture).atrules.media
 
@@ -427,6 +446,9 @@ AtRules('analyzes @keyframes', () => {
     @keyframes one {}
     @keyframes TWO {}
 
+    /* No prelude */
+    @keyframes {}
+
     /* Prefixes */
     @-webkit-keyframes animation {}
     @-moz-keyframes animation {}
@@ -523,6 +545,9 @@ AtRules('analyzes container queries', () => {
       /* only applies when an inline-size container is available */
       h2 { font-size: calc(1.2em + 1cqi); }
     }
+
+    /* No prelude */
+    @container {}
   `
   const result = analyze(fixture)
   const actual = result.atrules.container
@@ -590,6 +615,9 @@ AtRules('analyzes @property', () => {
         }
       }
     }
+
+    /* No prelude */
+    @property {}
   `
   const actual = analyze(fixture).atrules.property
   const expected = {

src/index.js

@@ -178,53 +178,56 @@ export function analyze(css, options = {}) {
           break
         }
 
-        if (atRuleName === 'media') {
-          let prelude = stringifyNode(node.prelude)
-          medias.push(prelude, node.prelude.loc)
-          if (isMediaBrowserhack(node.prelude)) {
-            mediaBrowserhacks.push(prelude, node.prelude.loc)
+        // All the AtRules in here MUST have a prelude, we we can count their names
+        if (node.prelude !== null) {
+          if (atRuleName === 'media') {
+            let prelude = stringifyNode(node.prelude)
+            medias.push(prelude, node.prelude.loc)
+            if (isMediaBrowserhack(node.prelude)) {
+              mediaBrowserhacks.push(prelude, node.prelude.loc)
+            }
+            break
           }
-          break
-        }
-        if (atRuleName === 'supports') {
-          let prelude = stringifyNode(node.prelude)
-          supports.push(prelude, node.prelude.loc)
-          if (isSupportsBrowserhack(node.prelude)) {
-            supportsBrowserhacks.push(prelude, node.prelude.loc)
+          if (atRuleName === 'supports') {
+            let prelude = stringifyNode(node.prelude)
+            supports.push(prelude, node.prelude.loc)
+            if (isSupportsBrowserhack(node.prelude)) {
+              supportsBrowserhacks.push(prelude, node.prelude.loc)
+            }
+            break
           }
-          break
-        }
-        if (endsWith('keyframes', atRuleName)) {
-          let name = '@' + atRuleName + ' ' + stringifyNode(node.prelude)
-          if (hasVendorPrefix(atRuleName)) {
-            prefixedKeyframes.push(name, node.prelude.loc)
+          if (endsWith('keyframes', atRuleName)) {
+            let name = '@' + atRuleName + ' ' + stringifyNode(node.prelude)
+            if (hasVendorPrefix(atRuleName)) {
+              prefixedKeyframes.push(name, node.prelude.loc)
+            }
+            keyframes.push(name, node.prelude.loc)
+            break
+          }
+          if (atRuleName === 'import') {
+            imports.push(stringifyNode(node.prelude), node.prelude.loc)
+            break
+          }
+          if (atRuleName === 'charset') {
+            charsets.push(stringifyNode(node.prelude), node.prelude.loc)
+            break
+          }
+          if (atRuleName === 'container') {
+            containers.push(stringifyNode(node.prelude), node.prelude.loc)
+            break
+          }
+          if (atRuleName === 'layer') {
+            let prelude = stringifyNode(node.prelude)
+            prelude
+              .split(',')
+              .forEach(name => layers.push(name.trim(), node.prelude.loc))
+            break
+          }
+          if (atRuleName === 'property') {
+            let prelude = stringifyNode(node.prelude)
+            registeredProperties.push(prelude, node.prelude.loc)
+            break
           }
-          keyframes.push(name, node.prelude.loc)
-          break
-        }
-        if (atRuleName === 'import') {
-          imports.push(stringifyNode(node.prelude), node.prelude.loc)
-          break
-        }
-        if (atRuleName === 'charset') {
-          charsets.push(stringifyNode(node.prelude), node.prelude.loc)
-          break
-        }
-        if (atRuleName === 'container') {
-          containers.push(stringifyNode(node.prelude), node.prelude.loc)
-          break
-        }
-        if (atRuleName === 'layer') {
-          let prelude = stringifyNode(node.prelude)
-          prelude
-            .split(',')
-            .forEach(name => layers.push(name.trim(), node.prelude.loc))
-          break
-        }
-        if (atRuleName === 'property') {
-          let prelude = stringifyNode(node.prelude)
-          registeredProperties.push(prelude, node.prelude.loc)
-          break
         }
         break
       }