fix(issue#4354): unknown at-rule expression commas

* Fix issue #4354 unknown at-rule expressions should not have commas in
  a keyword list.
* Add some additional layer at-rule tests.
* Fix broken CDN link so tests pass.

Author: puckowski

packages/less/src/less/tree/atrule.js

@@ -135,9 +135,6 @@ AtRule.prototype = Object.assign(new Node(), {
 
         if (value) {
             value = value.eval(context);
-            if (value.value && this.keywordList(value.value)) {
-                value = new Anonymous(value.value.map(keyword => keyword.value).join(', '), this.getIndex(), this.fileInfo());
-            }
         }
 
         if (rules) {

packages/test-data/tests-unit/import/import-remote.less

@@ -1,7 +1,7 @@
 // https://github.com/less/less.js/issues/3541
 @import (reference) url(https://cdn.jsdelivr.net/npm/@less/test-data/less/_main/selectors.less);
 @import (reference) url("https://cdn.jsdelivr.net/npm/@less/test-data/less/_main/media.less");
-@import (reference) url("https://cdn.jsdelivr.net/npm/@less/test-data/less/_main/empty.less?arg");
+@import (reference) url("https://cdn.jsdelivr.net/gh/less/[email protected]/packages/test-data/less/_main/empty.less?arg");
 
 .test {
   color: @var;

packages/test-data/tests-unit/layer/layer.css

@@ -91,3 +91,43 @@
     color: #555;
   }
 }
+@layer theme;
+@layer layout, utilities;
+body {
+  color: black;
+}
+@layer components {
+  .btn {
+    color: red;
+  }
+  .btn:hover {
+    color: blue;
+  }
+}
+@layer {
+  p {
+    margin-block: 1rem;
+  }
+}
+@layer framework.buttons.primary {
+  .btn-primary {
+    background: dodgerblue;
+    color: white;
+  }
+}
+.feature {
+  color: gray;
+}
+@layer component {
+  .feature h2 {
+    font-size: 1.5rem;
+  }
+}
+@layer ui {
+  .btn {
+    padding: 0.5rem 1rem;
+    border-radius: 4px;
+    background: rebeccapurple;
+    color: white;
+  }
+}

packages/test-data/tests-unit/layer/layer.less

@@ -112,3 +112,56 @@
 }
 
 
+@layer theme;
+@layer layout, utilities;
+
+body {
+  color: black;
+}
+
+@layer components {
+  .btn {
+    color: red;
+    &:hover {
+      color: blue;
+    }
+  }
+}
+
+@layer {
+  p {
+    margin-block: 1rem;
+  }
+}
+
+@layer framework.buttons.primary {
+  .btn-primary {
+    background: dodgerblue;
+    color: white;
+  }
+}
+
+.feature {
+  color: gray;
+
+  @layer component {
+    h2 {
+      font-size: 1.5rem;
+    }
+  }
+}
+
+@primary-color: rebeccapurple;
+
+.button-styles() {
+  padding: 0.5rem 1rem;
+  border-radius: 4px;
+}
+
+@layer ui {
+  .btn {
+    .button-styles();
+    background: @primary-color;
+    color: white;
+  }
+}

packages/test-data/tests-unit/tailwind/tailwind.css

@@ -0,0 +1,3 @@
+.box {
+  @apply h-64 w-64;
+}

packages/test-data/tests-unit/tailwind/tailwind.less

@@ -0,0 +1,3 @@
+.box {
+  @apply h-64 w-64;
+}