Gulpfile for LESS compilation with external sourcemap file support

gulp-less-sourcemap-config.js

var gulp = require('gulp');
var less = require('gulp-less');
var path = require('path');//
var fs = require('fs');

var ensureDirectory = function (filepath) {
    var dir = path.dirname(filepath),
        cmd,
        existsSync = fs.existsSync || path.existsSync;
    if (!existsSync(dir)) {
        if (mkdirp === undefined) {
            try {mkdirp = require('mkdirp');}
            catch(e) { mkdirp = null; }
        }
        cmd = mkdirp && mkdirp.sync || fs.mkdirSync;
        cmd(dir);
    }
};

var lessing = function () {
	gulp
		.src('./style.less')
		.pipe(
			less(function (file) {
				var filePath = file.path,
					surceMapFileName = path.basename(file.path, '.less') + '.map',
					sourceMapFilePath = path.join(path.dirname(filePath), surceMapFileName)
			
				return {
					writeSourceMap: function (output) {
						ensureDirectory(sourceMapFilePath);
						fs.writeFileSync(sourceMapFilePath, output, 'utf8');
					},
					sourceMapURL: surceMapFileName,
					sourceMap: sourceMapFilePath,
					sourceMapRootpath: '',
					sourceMapBasepath: path.dirname(filePath),
					paths: [ path.join(__dirname) ]
				}
			})
		)
		.pipe(gulp.dest('./'));
}

gulp.task('default', function() {
	lessing()
});

/*gulp.watch('./style.less', function () {
	lessing()
})*/

index(gulp-lib).js

var less = require('less');
var through2 = require('through2');
var gutil = require('gulp-util');
var PluginError = gutil.PluginError;
var path = require('path');
var defaults = require('lodash.defaults');

module.exports = function (options) {

  function transform (file, enc, next) {
    var self = this;

    if (file.isNull()) {
      this.push(file); // pass along
      return next();
    }

    if (file.isStream()) {
      this.emit('error', new PluginError('gulp-less', 'Streaming not supported'));
      return next();
    }

    var str = file.contents.toString('utf8');
	
	var opts = {};
	
	if (typeof options === 'function') {
		opts = options.apply(this, arguments);
	}
	
	// Mixes in default options.
	opts = defaults(opts || {}, {
		compress: false,
		paths: []
	});

    // Injects the path of the current file.
    opts.filename = file.path;

    less.render(str, opts, function (err, css) {
      if (err) {

        // convert the keys so PluginError can read them
        err.lineNumber = err.line;
        err.fileName = err.filename;

        // add a better error message
        err.message = err.message + ' in file ' + err.fileName + ' line no. ' + err.lineNumber;

        self.emit('error', new PluginError('gulp-less', err));
      } else {
        file.contents = new Buffer(css);
        file.path = gutil.replaceExtension(file.path, '.css');
        self.push(file);
      }
      next();
    });
  }

  return through2.obj(transform);
};