add debug messages

lib/6to5/file.js

@@ -323,6 +323,8 @@ File.prototype.parse = function (code) {
 File.prototype.transform = function (ast) {
   var self = this;
 
+  util.debug(this.opts.filename);
+
   this.ast = ast;
   this.lastStatements = t.getLastStatements(ast.program);
   this.scope = new Scope(ast.program, ast, null, this);

lib/6to5/transformation/transformer-pass.js

@@ -1,6 +1,7 @@
 module.exports = TransformerPass;
 
 var traverse = require("../traverse");
+var util     = require("../util");
 var _        = require("lodash");
 
 /**
@@ -60,6 +61,8 @@ var transformVisitor = {
 TransformerPass.prototype.transform = function () {
   var file = this.file;
 
+  util.debug(file.opts.filename + ": Running transformer " + this.transformer.key);
+
   this.astRun("before");
 
   var state = { file: file, handlers: this.handlers, pass: this };

lib/6to5/util.js

@@ -5,6 +5,7 @@ require("./patch");
 var estraverse = require("estraverse");
 var codeFrame  = require("./helpers/code-frame");
 var traverse   = require("./traverse");
+var debug      = require("debug");
 var acorn      = require("acorn-6to5");
 var path       = require("path");
 var util       = require("util");
@@ -14,6 +15,8 @@ var _          = require("lodash");
 
 exports.inherits = util.inherits;
 
+exports.debug = debug("6to5");
+
 exports.canCompile = function (filename, altExts) {
   var exts = altExts || exports.canCompile.EXTENSIONS;
   var ext = path.extname(filename);

package.json

@@ -38,6 +38,7 @@
     "chokidar": "0.12.6",
     "commander": "2.6.0",
     "core-js": "^0.4.9",
+    "debug": "^2.1.1",
     "detect-indent": "3.0.0",
     "estraverse": "1.9.1",
     "esutils": "1.1.6",