add support for using detached rulesets

Author: Horcrux7

src/com/inet/lib/less/LessParser.java

@@ -417,7 +417,11 @@ private void variable( HashMap<String, Expression> variables, FormattableContain
                         importFile( currentRule, name.substring( 8 ).trim() );
                         return;
                     }
-                    currentRule.add( new CssAtRule( reader, name + ';') ); // directives like @charset "UTF-8";
+                    if( name.endsWith( "()" ) ) {
+                        currentRule.add( new VariableExpression( reader, name.substring( 0, name.length() - 2 ) ) ); // reference to detached ruleset
+                    } else {
+                        currentRule.add( new CssAtRule( reader, name + ';') ); // directives like @charset "UTF-8";
+                    }
                     return;
 //                    throw createException( "Unrecognized input: '" + name + "'" );
                 default:

src/com/inet/lib/less/ValueExpression.java

@@ -1,7 +1,7 @@
 /**
  * MIT License (MIT)
  *
- * Copyright (c) 2014 - 2016 Volker Berlin
+ * Copyright (c) 2014 - 2019 Volker Berlin
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -42,6 +42,8 @@ class ValueExpression extends Expression {
 
     private Operation op;
 
+    private Rule      rule;
+
     /**
      * Create a new instance.
      * @param obj another LessObject with parse position.
@@ -83,6 +85,7 @@ class ValueExpression extends Expression {
      */
     ValueExpression( Rule rule ) {
         super( rule, "" );
+        this.rule = rule;
         this.type = RULESET;
         this.unit = "";
     }
@@ -133,6 +136,9 @@ public void appendTo( CssFormatter formatter ) {
             case STRING:
                 SelectorUtils.appendToWithPlaceHolder( formatter, toString(), 0, true, this );
                 break;
+            case RULESET:
+                rule.appendPropertiesTo( formatter );
+                break;
             default:
                 super.appendTo( formatter );
         }