Expose Less parsing as a top level feature of the less package

Converting a Less stylesheet into an AST is a valuable piece of
functionality, and worthy of being easily accessible to consumers
of less.js.

lib/less/index.js

@@ -17,6 +17,7 @@ module.exports = function(environment, fileManagers) {
         ParseTree: (ParseTree = require('./parse-tree')(SourceMapBuilder)),
         ImportManager: (ImportManager = require('./import-manager')(environment)),
         render: require("./render")(environment, ParseTree, ImportManager),
+        parse: require("./parse")(environment, ParseTree, ImportManager),
         LessError: require('./less-error'),
         transformTree: require('./transform-tree'),
         utils: require('./utils'),

lib/less/parse.js

@@ -0,0 +1,61 @@
+var PromiseConstructor = typeof Promise === 'undefined' ? require('promise') : Promise,
+    contexts = require("./contexts"),
+    Parser = require('./parser/parser'),
+    PluginManager = require('./plugin-manager');
+
+module.exports = function(environment, ParseTree, ImportManager) {
+    var parse = function (input, options, callback) {
+        options = options || {};
+
+        if (typeof(options) === 'function') {
+            callback = options;
+            options = {};
+        }
+
+        if (!callback) {
+            var self = this;
+            return new PromiseConstructor(function (resolve, reject) {
+                parse.call(self, input, options, function(err, output) {
+                    if (err) {
+                        reject(err);
+                    } else {
+                        resolve(output);
+                    }
+                });
+            });
+        } else {
+            var context,
+                rootFileInfo,
+                pluginManager = new PluginManager(this);
+
+            pluginManager.addPlugins(options.plugins);
+            options.pluginManager = pluginManager;
+
+            context = new contexts.Parse(options);
+
+            if (options.rootFileInfo) {
+                rootFileInfo = options.rootFileInfo;
+            } else {
+                var filename = options.filename || "input";
+                var entryPath = filename.replace(/[^\/\\]*$/, "");
+                rootFileInfo = {
+                    filename: filename,
+                    relativeUrls: context.relativeUrls,
+                    rootpath: context.rootpath || "",
+                    currentDirectory: entryPath,
+                    entryPath: entryPath,
+                    rootFilename: filename
+                };
+            }
+
+            var imports = new ImportManager(context, rootFileInfo);
+
+            new Parser(context, imports, rootFileInfo)
+                .parse(input, function (e, root) {
+                if (e) { return callback(e); }
+                callback(null, root, imports, options);
+            }, options);
+        }
+    };
+    return parse;
+};

lib/less/render.js

@@ -1,11 +1,8 @@
-var PromiseConstructor = typeof Promise === 'undefined' ? require('promise') : Promise,
-    contexts = require("./contexts"),
-    Parser = require('./parser/parser'),
-    PluginManager = require('./plugin-manager');
+var PromiseConstructor = typeof Promise === 'undefined' ? require('promise') : Promise;
 
 module.exports = function(environment, ParseTree, ImportManager) {
     var render = function (input, options, callback) {
-        options = options || {};
+        var parse = require('./parse')(environment, ParseTree, ImportManager);
 
         if (typeof(options) === 'function') {
             callback = options;
@@ -24,44 +21,20 @@ module.exports = function(environment, ParseTree, ImportManager) {
                 });
             });
         } else {
-            var context,
-                rootFileInfo,
-                pluginManager = new PluginManager(this);
+            parse(input, options, function(err, root, imports, options) {
+                if (err) { return callback(err); }
 
-            pluginManager.addPlugins(options.plugins);
-            options.pluginManager = pluginManager;
-
-            context = new contexts.Parse(options);
-
-            if (options.rootFileInfo) {
-                rootFileInfo = options.rootFileInfo;
-            } else {
-                var filename = options.filename || "input";
-                var entryPath = filename.replace(/[^\/\\]*$/, "");
-                rootFileInfo = {
-                    filename: filename,
-                    relativeUrls: context.relativeUrls,
-                    rootpath: context.rootpath || "",
-                    currentDirectory: entryPath,
-                    entryPath: entryPath,
-                    rootFilename: filename
-                };
-            }
-
-            var imports = new ImportManager(context, rootFileInfo);
-
-            new Parser(context, imports, rootFileInfo)
-                .parse(input, function (e, root) {
-                if (e) { return callback(e); }
                 var result;
                 try {
                     var parseTree = new ParseTree(root, imports);
                     result = parseTree.toCSS(options);
                 }
-                catch (err) { return callback( err); }
+                catch (err) { return callback(err); }
+
                 callback(null, result);
-            }, options);
+            });
         }
     };
+
     return render;
 };