Minor performance optimization

* Minor performance optimization for at rule check.

Author: puckowski

dist/less.js

@@ -2952,6 +2952,12 @@
             skipWhitespace(1);
             return tok;
         };
+        parserInput.$peekChar = function (tok) {
+            if (input.charAt(parserInput.i) !== tok) {
+                return null;
+            }
+            return tok;
+        };
         parserInput.$str = function (tok) {
             var tokLength = tok.length;
             // https://jsperf.com/string-startswith/21
@@ -4910,11 +4916,13 @@
                         debugInfo = getDebugInfo(index);
                     }
                     parserInput.save();
-                    if (parserInput.$str('@media')) {
-                        return this.prepareAndGetNestableAtRule(tree.Media, index, debugInfo, MediaSyntaxOptions);
-                    }
-                    if (parserInput.$str('@container')) {
-                        return this.prepareAndGetNestableAtRule(tree.Container, index, debugInfo, ContainerSyntaxOptions);
+                    if (parserInput.$peekChar('@')) {
+                        if (parserInput.$str('@media')) {
+                            return this.prepareAndGetNestableAtRule(tree.Media, index, debugInfo, MediaSyntaxOptions);
+                        }
+                        if (parserInput.$str('@container')) {
+                            return this.prepareAndGetNestableAtRule(tree.Container, index, debugInfo, ContainerSyntaxOptions);
+                        }
                     }
                     parserInput.restore();
                 },

dist/less.min.js

@@ -2952,6 +2952,12 @@
             skipWhitespace(1);
             return tok;
         };
+        parserInput.$peekChar = function (tok) {
+            if (input.charAt(parserInput.i) !== tok) {
+                return null;
+            }
+            return tok;
+        };
         parserInput.$str = function (tok) {
             var tokLength = tok.length;
             // https://jsperf.com/string-startswith/21
@@ -4910,11 +4916,13 @@
                         debugInfo = getDebugInfo(index);
                     }
                     parserInput.save();
-                    if (parserInput.$str('@media')) {
-                        return this.prepareAndGetNestableAtRule(tree.Media, index, debugInfo, MediaSyntaxOptions);
-                    }
-                    if (parserInput.$str('@container')) {
-                        return this.prepareAndGetNestableAtRule(tree.Container, index, debugInfo, ContainerSyntaxOptions);
+                    if (parserInput.$peekChar('@')) {
+                        if (parserInput.$str('@media')) {
+                            return this.prepareAndGetNestableAtRule(tree.Media, index, debugInfo, MediaSyntaxOptions);
+                        }
+                        if (parserInput.$str('@container')) {
+                            return this.prepareAndGetNestableAtRule(tree.Container, index, debugInfo, ContainerSyntaxOptions);
+                        }
                     }
                     parserInput.restore();
                 },

dist/less.min.js.map

@@ -149,6 +149,13 @@ export default () => {
         return tok;
     };
 
+    parserInput.$peekChar = tok => {
+        if (input.charAt(parserInput.i) !== tok) {
+            return null;
+        }
+        return tok;
+    };
+
     parserInput.$str = tok => {
         const tokLength = tok.length;
 

packages/less/dist/less.js

@@ -1845,12 +1845,14 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                 }
                 parserInput.save();
 
-                if (parserInput.$str('@media')) {
-                    return this.prepareAndGetNestableAtRule(tree.Media, index, debugInfo, MediaSyntaxOptions);
-                }
-                
-                if (parserInput.$str('@container')) {
-                    return this.prepareAndGetNestableAtRule(tree.Container, index, debugInfo, ContainerSyntaxOptions);
+                if (parserInput.$peekChar('@')) {
+                    if (parserInput.$str('@media')) {
+                        return this.prepareAndGetNestableAtRule(tree.Media, index, debugInfo, MediaSyntaxOptions);
+                    }
+                    
+                    if (parserInput.$str('@container')) {
+                        return this.prepareAndGetNestableAtRule(tree.Container, index, debugInfo, ContainerSyntaxOptions);
+                    }
                 }
 
                 parserInput.restore();