This adds an additional vars parameter to the parse method. It allows a user to inject variables into a less string before compiling.

lib/less/browser.js

@@ -595,16 +595,6 @@ function initRunningMode(){
     }
 }
 
-function serializeVars(vars) {
-    var s = "";
-
-    for (var name in vars) {
-        s += ((name.slice(0,1) === '@')? '' : '@') + name +': '+
-                ((vars[name].slice(-1) === ';')? vars[name] : vars[name] +';');
-    }
-
-    return s;
-}
 
 
 //
@@ -649,7 +639,7 @@ for (var i = 0; i < links.length; i++) {
 // CSS without reloading less-files
 //
 less.modifyVars = function(record) {
-    less.refresh(false, serializeVars(record));
+    less.refresh(false, less.Parser.serializeVars(record));
 };
 
 less.refresh = function (reload, newVars) {
@@ -677,7 +667,7 @@ less.refresh = function (reload, newVars) {
 };
 
 if (less.globalVars) {
-    varsPre = serializeVars(less.globalVars) + "\n";
+    varsPre = less.Parser.serializeVars(less.globalVars) + "\n";
 }
 
 less.refreshStyles = loadStyles;

lib/less/parser.js

@@ -295,13 +295,17 @@ less.Parser = function Parser(env) {
         imports: imports,
         //
         // Parse an input string into an abstract syntax tree,
-        // call `callback` when done.
+        // @param str A string containing 'less' markup
+        // @param callback call `callback` when done.
+        // @param [vars] An optional map (key, value) of variables to apply
         //
-        parse: function (str, callback) {
+        parse: function (str, callback, vars) {
             var root, line, lines, error = null;
 
             i = j = current = furthest = 0;
-            input = str.replace(/\r\n/g, '\n');
+
+            vars = vars ? less.Parser.serializeVars(vars) + '\n' : '';
+            input = (vars + str).replace(/\r\n/g, '\n');
 
             // Remove potential UTF Byte Order Mark
             input = input.replace(/^\uFEFF/, '');
@@ -1726,4 +1730,17 @@ less.Parser = function Parser(env) {
         }
     };
 };
+less.Parser.serializeVars = function(vars) {
+    var s = '';
+
+    for (var name in vars) {
+        if (Object.hasOwnProperty.call(vars, name)) {
+            var value = vars[name];
+            s += ((name[0] === '@') ? '' : '@') + name +': '+ value +
+                    ((('' + value).slice(-1) === ';') ? '' : ';');
+        }
+    }
+
+    return s;
+};
 

test/css/parse/extended.css

@@ -0,0 +1,9 @@
+#header {
+  color: #333333;
+  border-left: 1px;
+  border-right: 2px;
+}
+#footer {
+  color: #114411;
+  border-color: #7d2717;
+}

test/css/parse/simple.css

@@ -0,0 +1,3 @@
+.class {
+  color: #ff0000;
+}

test/less-test.js

@@ -29,6 +29,8 @@ less.tree.functions._color = function (str) {
 console.log("\n" + stylize("LESS", 'underline') + "\n");
 
 runTestSet({strictMath: true, relativeUrls: true, silent: true});
+runTestSet({vars: true}, "parse/",
+            null, null, null, function(name) { return path.join('test/less/', name) + '.json'; });
 runTestSet({strictMath: true, strictUnits: true}, "errors/",
             testErrors, null, getErrorPathReplacementFunction("errors"));
 runTestSet({strictMath: true, strictUnits: true, javascriptEnabled: false}, "no-js-errors/",
@@ -122,10 +124,14 @@ function runTestSet(options, foldername, verifyFunction, nameModifier, doReplace
         doReplacements = globalReplacements;
     }
 
+    function getBasename(file) {
+        return foldername + path.basename(file, '.less');
+    }
+
     fs.readdirSync(path.join('test/less/', foldername)).forEach(function (file) {
         if (! /\.less/.test(file)) { return; }
         
-        var name = foldername + path.basename(file, '.less');
+        var name = getBasename(file);
         
         if (oneTestOnly && name !== oneTestOnly) {
             return;
@@ -143,6 +149,12 @@ function runTestSet(options, foldername, verifyFunction, nameModifier, doReplace
             options.sourceMapRootpath = "testweb/";
         }
 
+        if (options.vars) {
+            options.getVars = function(file) {
+                return JSON.parse(fs.readFileSync(getFilename(getBasename(file)), 'utf8'));
+            };
+        }
+
         toCSS(options, path.join('test/less/', foldername + file), function (err, less) {
 
             if (verifyFunction) {
@@ -232,7 +244,9 @@ function toCSS(options, path, callback) {
         options.filename = require('path').resolve(process.cwd(), path);
         options.optimization = options.optimization || 0;
 
-        new(less.Parser)(options).parse(str, function (err, tree) {
+        var parser = new(less.Parser)(options);
+        var args = [str];
+        args.push(function (err, tree) {
             if (err) {
                 callback(err);
             } else {
@@ -244,6 +258,10 @@ function toCSS(options, path, callback) {
                 }
             }
         });
+        if (options.vars) {
+            args.push(options.getVars(path));
+        }
+        parser.parse.apply(parser, args);
     });
 }
 

test/less/parse/extended.json

@@ -0,0 +1,5 @@
+{
+    "the-border": "1px",
+    "base-color": "#111",
+    "red": "#842210"
+}

test/less/parse/extended.less

@@ -0,0 +1,9 @@
+#header {
+  color: (@base-color * 3);
+  border-left: @the-border;
+  border-right: (@the-border * 2);
+}
+#footer {
+  color: (@base-color + #003300);
+  border-color: desaturate(@red, 10%);
+}

test/less/parse/simple.json

@@ -0,0 +1,3 @@
+{
+	"my-color": "red"
+}

test/less/parse/simple.less

@@ -0,0 +1,3 @@
+.class {
+  color: @my-color;
+}