Add a rtl and ltr variable

lib/index.js

@@ -1,8 +1,10 @@
-var getRTLPlugin = require("./rtl-plugin");
+var getRTLPlugin = require("./rtl-plugin"),
+    RTLVariablePlugin = require("./rtl-variable-plugin");
 
 module.exports = {
     install: function(less, pluginManager) {
         var RTLPlugin = getRTLPlugin(less);
         pluginManager.addVisitor(new RTLPlugin());
+        pluginManager.addPreProcessor(new RTLVariablePlugin());
     }
 };

lib/rtl-variable-plugin.js

@@ -0,0 +1,13 @@
+function RTLVariablePlugin() {
+}
+
+RTLVariablePlugin.prototype.process = function(src, extra) {
+    var variable = "@rtl: true; @ltr: false;\n"
+    var contentsIgnoredChars = extra.imports.contentsIgnoredChars;
+    var filename = extra.fileInfo.filename;
+    contentsIgnoredChars[filename] = contentsIgnoredChars[filename] || 0;
+    contentsIgnoredChars[filename] += variable.length;
+    return variable + src;
+};
+
+module.exports = RTLVariablePlugin;

test/css/rtl/test.css

@@ -14,3 +14,6 @@
   margin: 1px 7px 3px;
   margin: 1px 4px 3px 2px;
 }
+.rtl-only {
+  margin: 3px;
+}

test/less/rtl/test.less

@@ -20,4 +20,9 @@
   margin: @vertical @horizontal;
   margin: @top @horizontal @bottom;
   margin: @top @right @bottom @left;
+}
+& when (@rtl) {
+  .rtl-only {
+    margin: 3px;
+  }
 }