v5.2.3

This reverts commit c3c4cf17e3.

.babelrc

@@ -1,6 +1,6 @@
 {
-  "experimental": true,
-  "playground": true,
-  "loose": true,
-  "blacklist": ["es6.tailCall"]
+  "stage": 0,
+  "loose": ["all"],
+  "blacklist": ["es6.tailCall"],
+  "optional": ["optimisation.flow.forOf"]
 }

.gitmodules

@@ -1,12 +1,6 @@
 [submodule "vendor/traceur"]
 	path = vendor/traceur
 	url = https://github.com/google/traceur-compiler
-[submodule "vendor/regenerator"]
-	path = vendor/regenerator
-	url = https://github.com/babel/regenerator-babel
-[submodule "vendor/test262"]
-	path = vendor/test262
-	url = https://github.com/tc39/test262
 [submodule "vendor/compat-table"]
 	path = vendor/compat-table
 	url = https://github.com/kangax/compat-table

.travis.yml

@@ -1,4 +1,4 @@
-sudo: false
+#sudo: false
 language: node_js
 cache:
   directories:

CHANGELOG.md

@@ -13,6 +13,45 @@ _Note: Gaps between patch versions are faulty/broken releases._
 
 See [CHANGELOG - 6to5](CHANGELOG-6to5.md) for the pre-4.0.0 version changelog.
 
+## 5.2.3
+
+ * **Bug Fix**
+  * Fix plugin containers being called with an undefined import. Thanks [@timbur](https://github.com/timbur)!
+  * Allow Flow object separators to be commas. Thanks [@monsanto](https://github.com/monsanto)!
+  * Add missing `Statement` and `Declaration` node aliases to flow types.
+
+## 5.2.2
+
+ * **Internal**
+  * Allow `util.arrayify` to take arbitrary types and coerce it into an array.
+
+## 5.2.1
+
+ * **Bug Fix**
+  * Fix regression in `node/register` that caused `node_modules` to not be ignored.
+
+## 5.2.0
+
+ * **Bug Fix**
+  * Fix plugin strings splitting arbitrarily on `:` which caused full paths on Windows to fail as they include `:` after the drive letter.
+  * Call class property `initializer`s with their target instead of their descriptor.
+  * Fix `ignore` and `only` not properly working on Windows path separators. Thanks [@stagas](https://github.com/stagas)!
+  * Fix `resolveRc` running on files twice causing issues. Thanks [@lukescott](https://github.com/lukescott)!
+  * Fix shorthand properties not correctly being target for `isReferenced` checks. Thanks [@monsanto](https://github.com/monsanto)!
+ * **Polish**
+  * Allow passing an array of globs to `babel/register` `only` and `ignore` options. Thanks [@Mark-Simulacrum](https://github.com/Mark-Simulacrum)!
+  * When inferring function names that collide with upper bindings, instead of doing the wrapper, instead rename them.
+  * Consider constant-like variable declaration functions to always refer to themselves so TOC can be performed.
+  * Process globs manually when using `$ babel` as some shells such as Windows don't explode them. Thanks [@jden](https://github.com/jden)!
+  * Add alternative way to execute plugins via a closure that's called with the current Babel instance.
+ * **Internal**
+  * Remove multiple internal transformers in favor of directly doing things when we need to. Previously, declarations such as `_ref` that we needed to create in specific scopes were done at the very end via the `_declarations` transformer. Now, they're done and added to the scope **right** when they're needed. This gets rid of the crappy `_declarations` property on scope nodes and fixes the crappy regenerator bug where it was creating a new `BlockStatement` so the declarations were being lost.
+  * Rework transformer traversal optimisation. Turns out that calling a `check` function for **every single node** in the AST is ridiculously expensive. 300,000 nodes timesed by ~30 transformers meant that it took tens of seconds to perform while it's quicker to just do the unnecessary traversal. Seems obvious in hindsight.
+ * **New Feature**
+  * Add `jscript` transformer that turns named function expressions into function declarations to get around [JScript's horribly broken function expression semantics](https://kangax.github.io/nfe/#jscript-bugs). Thanks [@kondi](https://github.com/kondi)!
+  * Add `@@hasInstance` support to objects when using the `es6.spec.symbols` transformer.
+  * Add `retainLines` option that retains the line (but not the columns!) of the input code.
+
 ## 5.1.13
 
  * **Polish**

CONTRIBUTING.md

@@ -29,16 +29,19 @@ $ cd babel
 $ make bootstrap
 ```
 
-Then you need to run:
+Then you can either run:
+
+```sh
+$ make build-core
+```
+
+to build Babel **once** or:
 
 ```sh
 $ make watch-core
 ```
 
-This will compile Babel and then sit in the background and on file modification
-recompile the necessary files. Babel itself is written in ES6. The source files
-reside in `src/` and transpile to `lib/`
-
+to have Babel build itself then incrementally build files on change.
 
 #### Running tests
 

Makefile

@@ -9,17 +9,20 @@ BABEL_CMD = node_modules/babel/bin/babel
 
 export NODE_ENV = test
 
-.PHONY: clean test test-cov test-clean test-travis test-simple test-all test-browser test-parser publish build bootstrap publish-core publish-runtime build-core watch-core build-core-test
+.PHONY: clean test test-cov test-clean test-travis test-simple test-all test-browser test-parser publish build bootstrap publish-core publish-runtime build-core watch-core build-core-test clean-core
 
-build-core:
+build-core: clean-core
 	node $(BABEL_CMD) src --out-dir lib --copy-files
 
-build-core-test:
+build-core-test: clean-core
 	node $(BABEL_CMD) src --out-dir lib --copy-files --auxiliary-comment "istanbul ignore next"
 
-watch-core:
+watch-core: clean-core
 	node $(BABEL_CMD) src --out-dir lib --watch --copy-files
 
+clean-core:
+	rm -rf lib
+
 build:
 	mkdir -p dist
 	make build-core
@@ -115,3 +118,4 @@ bootstrap:
 	cd packages/babel-cli && npm install && npm link && npm link babel-core
 	git submodule update --init
 	cd vendor/compat-table && npm install object-assign
+	make build

package.json

@@ -1,7 +1,7 @@
 {
   "name": "babel-core",
   "description": "Turn ES6 code into readable vanilla ES5 with source maps",
-  "version": "5.1.13",
+  "version": "5.2.3",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
   "repository": "babel/babel",
@@ -28,6 +28,7 @@
   },
   "dependencies": {
     "ast-types": "~0.7.0",
+    "bluebird": "^2.9.25",
     "chalk": "^1.0.0",
     "convert-source-map": "^1.1.0",
     "core-js": "^0.9.0",
@@ -49,6 +50,7 @@
     "regenerator": "^0.8.20",
     "regexpu": "^1.1.2",
     "repeating": "^1.1.2",
+    "resolve": "^1.1.6",
     "shebang-regex": "^1.0.0",
     "slash": "^1.0.0",
     "source-map": "^0.4.0",
@@ -59,7 +61,7 @@
     "user-home": "^1.1.1"
   },
   "devDependencies": {
-    "babel": "4.7.13",
+    "babel": "5.1.13",
     "browserify": "^9.0.8",
     "chai": "^2.2.0",
     "eslint": "^0.18.0",

packages/babel-cli/bin/babel/index.js

@@ -8,6 +8,7 @@ var util      = require("babel-core").util;
 var each      = require("lodash/collection/each");
 var keys      = require("lodash/object/keys");
 var fs        = require("fs");
+var glob      = require("glob");
 
 each(options, function (option, key) {
   if (option.hidden) return;
@@ -69,7 +70,9 @@ commander.parse(process.argv);
 
 var errors = [];
 
-var filenames = commander.args;
+var filenames = commander.args.reduce(function (globbed, input) {
+  return globbed.concat(glob.sync(input));
+}, []);
 
 each(filenames, function (filename) {
   if (!fs.existsSync(filename)) {

packages/babel-cli/package.json

@@ -1,21 +1,22 @@
 {
   "name": "babel",
   "description": "Turn ES6 code into readable vanilla ES5 with source maps",
-  "version": "5.1.12",
+  "version": "5.2.2",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
   "repository": "babel/babel",
   "preferGlobal": true,
   "dependencies": {
-    "babel-core": "^5.1.12",
+    "babel-core": "^5.2.2",
     "chokidar": "^1.0.0",
     "commander": "^2.6.0",
-    "fs-readdir-recursive": "^0.1.0",
-    "output-file-sync": "^1.1.0",
-    "lodash": "^3.2.0",
     "convert-source-map": "^1.1.0",
-    "source-map": "^0.4.0",
-    "path-is-absolute": "^1.0.0"
+    "fs-readdir-recursive": "^0.1.0",
+    "glob": "^5.0.5",
+    "lodash": "^3.2.0",
+    "output-file-sync": "^1.1.0",
+    "path-is-absolute": "^1.0.0",
+    "source-map": "^0.4.0"
   },
   "bin": {
     "babel": "./bin/babel/index.js",

packages/babel-cli/register-without-polyfill.js

@@ -0,0 +1 @@
+module.exports = require("babel-core/register-without-polyfill");

packages/babel-runtime/package.json

@@ -1,7 +1,7 @@
 {
   "name": "babel-runtime",
   "description": "babel selfContained runtime",
-  "version": "5.1.12",
+  "version": "5.2.2",
   "repository": "babel/babel",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "dependencies": {

register-without-polyfill.js

@@ -0,0 +1 @@
+module.exports = require("./lib/babel/api/register/node");

register.js

@@ -1 +1 @@
-module.exports = require("./lib/babel/api/register/node");
+module.exports = require("./lib/babel/api/register/node-polyfill");

src/acorn/index.js

@@ -0,0 +1,3 @@
+export * from "./src/index";
+import "./plugins/flow";
+import "./plugins/jsx";

src/acorn/package.json

@@ -2,7 +2,7 @@
   "name": "acorn",
   "description": "ECMAScript parser",
   "homepage": "https://github.com/marijnh/acorn",
-  "main": "src/index.js",
+  "main": "index.js",
   "version": "1.0.0",
   "engines": {
     "node": ">=0.4.0"

src/acorn/plugins/flow.js

@@ -1,4 +1,4 @@
-var acorn = require("..")
+var acorn = require("../src/index")
 
 var pp = acorn.Parser.prototype
 var tt = acorn.tokTypes
@@ -322,7 +322,7 @@ pp.flow_parseObjectType = function (allowStatic) {
 }
 
 pp.flow_objectTypeSemicolon = function () {
-  if (!this.eat(tt.semi) && this.type !== tt.braceR) {
+  if (!this.eat(tt.semi) && !this.eat(tt.comma) && this.type !== tt.braceR) {
     this.unexpected()
   }
 }

src/acorn/plugins/jsx.js

@@ -1,4 +1,4 @@
-var acorn = require("..")
+var acorn = require("../src/index")
 
 var tt = acorn.tokTypes;
 var tc = acorn.tokContexts;

src/acorn/src/index.js

@@ -38,9 +38,6 @@ export {isIdentifierChar, isIdentifierStart} from "./identifier"
 export {Token} from "./tokenize"
 export {isNewLine, lineBreak, lineBreakG} from "./whitespace"
 
-import "../plugins/flow";
-import "../plugins/jsx";
-
 export const version = "1.0.0"
 
 // The main exported interface (under `self.acorn` when in the

src/babel/api/browser.js

@@ -11,7 +11,7 @@ transform.run = function (code, opts = {}) {
 };
 
 transform.load = function (url, callback, opts = {}, hold) {
-  opts.filename ||= url;
+  opts.filename = opts.filename || url;
 
   var xhr = global.ActiveXObject ? new global.ActiveXObject("Microsoft.XMLHTTP") : new global.XMLHttpRequest();
   xhr.open("GET", url, true);

src/babel/api/node.js

@@ -9,6 +9,7 @@ export { canCompile } from "../util";
 
 export { default as options } from "../transformation/file/options";
 export { default as Transformer } from "../transformation/transformer";
+export { default as Pipeline } from "../transformation/transformer-pipeline";
 export { default as traverse } from "../traversal";
 export { default as buildExternalHelpers } from "../tools/build-external-helpers";
 export { version } from "../../../package";
@@ -17,7 +18,7 @@ import * as t from "../types";
 export { t as types };
 
 export function register(opts?: Object) {
-  var callback = require("./register/node");
+  var callback = require("./register/node-polyfill");
   if (opts != null) callback(opts);
   return callback;
 }

src/babel/api/register/node-polyfill.js

@@ -0,0 +1,2 @@
+import "../../polyfill";
+export { default } from "./node";

src/babel/api/register/node.js

@@ -1,4 +1,3 @@
-import "../../polyfill";
 import sourceMapSupport from "source-map-support";
 import * as registerCache from "./cache";
 import resolveRc from "../../tools/resolve-rc";
@@ -32,8 +31,10 @@ var cache = registerCache.get();
 //
 
 var transformOpts = {};
-var ignoreRegex   = /node_modules/;
-var onlyRegex;
+
+var ignore;
+var only;
+
 var oldHandlers   = {};
 var maps          = {};
 
@@ -77,8 +78,11 @@ var compile = function (filename) {
 };
 
 var shouldIgnore = function (filename) {
-  filename = slash(filename);
-  return (ignoreRegex && ignoreRegex.test(filename)) || (onlyRegex && !onlyRegex.test(filename));
+  if (!ignore && !only) {
+    return /node_modules/.test(filename);
+  } else {
+    return util.shouldIgnore(filename, ignore || [], only || []);
+  }
 };
 
 var istanbulMonkey = {};
@@ -144,8 +148,8 @@ var hookExtensions = function (_exts) {
 hookExtensions(util.canCompile.EXTENSIONS);
 
 export default function (opts = {}) {
-  if (opts.only != null) onlyRegex = util.regexify(opts.only);
-  if (opts.ignore != null) ignoreRegex = util.regexify(opts.ignore);
+  if (opts.only != null) only = util.arrayify(opts.only, util.regexify);
+  if (opts.ignore != null) ignore = util.arrayify(opts.ignore, util.regexify);
 
   if (opts.extensions) hookExtensions(util.arrayify(opts.extensions));
 

src/babel/generation/buffer.js

@@ -70,14 +70,14 @@ export default class Buffer {
   }
 
   newline(i, removeLast) {
-    if (this.format.compact) return;
+    if (this.format.compact || this.format.retainLines) return;
 
     if (this.format.concise) {
       this.space();
       return;
     }
 
-    removeLast ||= false;
+    removeLast = removeLast || false;
 
     if (isNumber(i)) {
       i = Math.min(2, i);

src/babel/generation/generators/base.js

@@ -13,7 +13,7 @@ export function BlockStatement(node, print) {
     this.push("{");
     this.newline();
     print.sequence(node.body, { indent: true });
-    this.removeLast("\n");
+    if (!this.format.retainLines) this.removeLast("\n");
     this.rightBrace();
   }
 }

src/babel/generation/index.js

@@ -12,7 +12,7 @@ import * as t from "../types";
 
 class CodeGenerator {
   constructor(ast, opts, code) {
-    opts ||= {};
+    opts = opts || {};
 
     this.comments = ast.comments || [];
     this.tokens   = ast.tokens || [];
@@ -34,9 +34,10 @@ class CodeGenerator {
     }
 
     var format = {
+      retainLines: opts.retainLines,
       comments: opts.comments == null || opts.comments,
       compact: opts.compact,
-      quotes: CodeGenerator.findCommonStringDelimeter(code, tokens),
+      quotes: CodeGenerator.findCommonStringDelimiter(code, tokens),
       indent: {
         adjustMultilineComment: true,
         style: style,
@@ -48,14 +49,14 @@ class CodeGenerator {
       format.compact = code.length > 100000; // 100KB
 
       if (format.compact) {
-        console.error(messages.get("codeGeneratorDeopt", opts.filename, "100KB"));
+        console.error("[BABEL] " + messages.get("codeGeneratorDeopt", opts.filename, "100KB"));
       }
     }
 
     return format;
   }
 
-  static findCommonStringDelimeter(code, tokens) {
+  static findCommonStringDelimiter(code, tokens) {
     var occurences = {
       single: 0,
       double: 0
@@ -146,6 +147,22 @@ class CodeGenerator {
     return print;
   }
 
+  catchUp(node, parent) {
+    // catch up to this nodes newline if we're behind
+    if (node.loc && this.format.retainLines && this.buffer.buf) {
+      var needsParens = false;
+      if (parent && this.position.line < node.loc.start.line && t.isTerminatorless(parent)) {
+        needsParens = true;
+        this._push("(");
+      }
+      while (this.position.line < node.loc.start.line) {
+        this._push("\n");
+      }
+      return needsParens;
+    }
+    return false;
+  }
+
   print(node, parent, opts = {}) {
     if (!node) return;
 
@@ -197,6 +214,8 @@ class CodeGenerator {
 
       this.printLeadingComments(node, parent);
 
+      var needsParensFromCatchup = this.catchUp(node, parent);
+
       newline(true);
 
       if (opts.before) opts.before();
@@ -208,7 +227,7 @@ class CodeGenerator {
         this.newline();
         this.dedent();
       }
-      if (needsParens) this.push(")");
+      if (needsParens || needsParensFromCatchup) this.push(")");
 
       this.map.mark(node, "end");
       if (opts.after) opts.after();
@@ -328,6 +347,8 @@ class CodeGenerator {
 
       if (skip) return;
 
+      this.catchUp(comment);
+
       // whitespace before
       this.newline(this.whitespace.getNewlinesBefore(comment));
 
@@ -340,7 +361,6 @@ class CodeGenerator {
       }
 
       //
-
       if (comment.type === "Block" && this.format.indent.adjustMultilineComment) {
         var offset = comment.loc.start.column;
         if (offset) {
@@ -356,8 +376,13 @@ class CodeGenerator {
         val = this.getIndent() + val;
       }
 
-      //
+      // force a newline for line comments when retainLines is set in case the next printed node
+      // doesn't catch up
+      if (this.format.retainLines && comment.type === "Line") {
+        val += "\n";
+      }
 
+      //
       this._push(val);
 
       // whitespace after

src/babel/generation/node/index.js

@@ -85,16 +85,7 @@ export default class Node {
       return false;
     }
 
-    if (t.isYieldExpression(parent) || t.isAwaitExpression(parent)) {
-      return true;
-    }
-
-    if (t.isContinueStatement(parent) || t.isBreakStatement(parent) ||
-        t.isReturnStatement(parent) || t.isThrowStatement(parent)) {
-      return true;
-    }
-
-    return false;
+    return t.isTerminatorless(parent);
   }
 }
 

src/babel/generation/node/parentheses.js

@@ -171,4 +171,10 @@ export function ConditionalExpression(node, parent) {
   return false;
 }
 
-export { ConditionalExpression as AssignmentExpression };
+export function AssignmentExpression(node) {
+  if (t.isObjectPattern(node.left)) {
+    return true;
+  } else {
+    return ConditionalExpression(...arguments);
+  }
+}

src/babel/generation/node/whitespace.js

@@ -16,7 +16,7 @@ function crawl(node, state = {}) {
   } else if (t.isFunction(node)) {
     state.hasFunction = true;
   } else if (t.isIdentifier(node)) {
-    state.hasHelper ||= isHelper(node.callee);
+    state.hasHelper = state.hasHelper || isHelper(node.callee);
   }
 
   return state;

src/babel/messages.js

@@ -22,7 +22,19 @@ export const MESSAGES = {
   codeGeneratorDeopt: "Note: The code generator has deoptimised the styling of $1 as it exceeds the max of $2.",
   missingTemplatesDirectory: "no templates directory - this is most likely the result of a broken `npm publish`. Please report to https://github.com/babel/babel/issues",
   unsupportedOutputType: "Unsupported output type $1",
-  illegalMethodName: "Illegal method name $1"
+  illegalMethodName: "Illegal method name $1",
+  traverseNeedsParent: "Must pass a scope and parentPath unless traversing a Program/File got a $1 node",
+  traverseVerifyRootFunction: "You passed `traverse()` a function when it expected a visitor object, are you sure you didn't mean `{ enter: Function }`?",
+  traverseVerifyVisitorFunction: "Hey! You passed \`traverse()\` a visitor object with the key $1 that's a straight up `Function` instead of `{ enter: Function }`. You need to normalise it with `traverse.explode(visitor)`.",
+  traverseVerifyVisitorProperty: "You passed `traverse()` a visitor object with the property $1 that has the invalid property $2",
+
+  pluginIllegalKind: "Illegal kind $1 for plugin $2",
+  pluginIllegalPosition: "Illegal position $1 for plugin $2",
+  pluginKeyCollision: "The plugin $1 collides with another of the same name",
+  pluginNotTransformer: "The plugin $1 didn't export a Transformer instance",
+  pluginUnknown: "Unknown plugin $1",
+
+  transformerNotFile: "Transformer $1 is resolving to a different Babel version to what is doing the actual transformation..."
 };
 
 export function get(key: String, ...args) {

src/babel/patch.js

@@ -55,4 +55,18 @@ def("ExportNamedDeclaration")
   )])
   .field("source", or(def("ModuleSpecifier"), null));
 
+def("ExportNamespaceSpecifier")
+  .bases("Specifier")
+  .field("exported", def("Identifier"));
+
+def("ExportDefaultSpecifier")
+  .bases("Specifier")
+  .field("exported", def("Identifier"));
+
+def("ExportAllDeclaration")
+  .bases("Declaration")
+  .build("exported", "source")
+  .field("exported", def("Identifier"))
+  .field("source", def("Literal"));
+
 types.finalize();

src/babel/tools/resolve-rc.js

@@ -33,7 +33,7 @@ export default function (loc, opts = {}) {
       var json;
 
       try {
-        json = jsons[content] ||= JSON.parse(stripJsonComments(content));
+        json = jsons[content] = jsons[content] || JSON.parse(stripJsonComments(content));
       } catch (err) {
         err.message = `${file}: ${err.message}`;
         throw err;
@@ -47,7 +47,7 @@ export default function (loc, opts = {}) {
           var c = a.slice(0);
           for (var v of b) {
             if (a.indexOf(v) < 0) {
-              c.push(v); 
+              c.push(v);
             }
           }
           return c;

src/babel/transformation/file/index.js

@@ -1,5 +1,7 @@
 import convertSourceMap from "convert-source-map";
 import * as optionParsers from "./option-parsers";
+import moduleFormatters from "../modules";
+import PluginManager from "./plugin-manager";
 import shebangRegex from "shebang-regex";
 import TraversalPath from "../../traversal/path";
 import isFunction from "lodash/lang/isFunction";
@@ -18,38 +20,40 @@ import Scope from "../../traversal/scope";
 import slash from "slash";
 import clone from "lodash/lang/clone";
 import * as util from  "../../util";
+import * as api from  "../../api/node";
 import path from "path";
 import each from "lodash/collection/each";
 import * as t from "../../types";
 
 var checkTransformerVisitor = {
-  enter(node, parent, scope, state) {
-    checkNode(state.stack, node, scope);
+  exit(node, parent, scope, state) {
+    checkPath(state.stack, this);
   }
 };
 
-function checkNode(stack, node, scope) {
+function checkPath(stack, path) {
   each(stack, function (pass) {
     if (pass.shouldRun || pass.ran) return;
-    pass.checkNode(node, scope);
+    pass.checkPath(path);
   });
 }
 
 export default class File {
-  constructor(opts = {}) {
+  constructor(opts = {}, pipeline) {
     this.dynamicImportTypes = {};
     this.dynamicImportIds   = {};
     this.dynamicImports     = [];
 
-    this.usedHelpers = {};
-    this.dynamicData = {};
-    this.data        = {};
-    this.uids        = {};
+    this.declarations = {};
+    this.usedHelpers  = {};
+    this.dynamicData  = {};
+    this.data         = {};
+    this.uids         = {};
 
-    this.lastStatements = [];
-    this.log            = new Logger(this, opts.filename || "unknown");
-    this.opts           = this.normalizeOptions(opts);
-    this.ast            = {};
+    this.pipeline = pipeline;
+    this.log      = new Logger(this, opts.filename || "unknown");
+    this.opts     = this.normalizeOptions(opts);
+    this.ast      = {};
 
     this.buildTransformers();
   }
@@ -85,6 +89,7 @@ export default class File {
     "temporal-assert-defined",
     "self-global",
     "default-props",
+    "instanceof",
 
     // legacy
     "interop-require",
@@ -130,10 +135,10 @@ export default class File {
       }
 
       var optionParser = optionParsers[option.type];
-      if (optionParser) val = optionParser(key, val);
+      if (optionParser) val = optionParser(key, val, this.pipeline);
 
       if (option.alias) {
-        opts[option.alias] ||= val;
+        opts[option.alias] = opts[option.alias] || val;
       } else {
         opts[key] = val;
       }
@@ -197,7 +202,7 @@ export default class File {
     var stack = [];
 
     // build internal transformers
-    each(transform.transformers, function (transformer, key) {
+    each(this.pipeline.transformers, function (transformer, key) {
       var pass = transformers[key] = transformer.buildPass(file);
 
       if (pass.canTransform()) {
@@ -216,8 +221,14 @@ export default class File {
     // init plugins!
     var beforePlugins = [];
     var afterPlugins = [];
+    var pluginManager = new PluginManager({
+      file: this,
+      transformers: this.transformers,
+      before: beforePlugins,
+      after: afterPlugins
+    });
     for (var i = 0; i < file.opts.plugins.length; i++) {
-      this.addPlugin(file.opts.plugins[i], beforePlugins, afterPlugins);
+      pluginManager.add(file.opts.plugins[i]);
     }
     stack = beforePlugins.concat(stack, afterPlugins);
 
@@ -226,7 +237,7 @@ export default class File {
   }
 
   getModuleFormatter(type: string) {
-    var ModuleFormatter = isFunction(type) ? type : transform.moduleFormatters[type];
+    var ModuleFormatter = isFunction(type) ? type : moduleFormatters[type];
 
     if (!ModuleFormatter) {
       var loc = util.resolveRelative(type);
@@ -240,60 +251,6 @@ export default class File {
     return new ModuleFormatter(this);
   }
 
-  addPlugin(name, before, after) {
-    var position = "before";
-    var plugin;
-
-    if (name) {
-      if (typeof name === "object" && name.transformer) {
-        plugin = name.transformer;
-        position = name.position || position;
-      } else if (typeof name === "string") {
-        // this is a plugin in the form of "foobar" or "foobar:after"
-        // where the optional colon is the delimiter for plugin position in the transformer stack
-
-        [name, position = "before"] = name.split(":");
-
-        var loc = util.resolveRelative(name) || util.resolveRelative(`babel-plugin-${name}`);
-        if (loc) {
-          plugin = require(loc)
-        } else {
-          throw new ReferenceError(`Unknown plugin ${JSON.stringify(name)}`);
-        }
-      } else {
-        // not a string so we'll just assume that it's a direct Transformer instance, if not then
-        // the checks later on will complain
-        plugin = name;
-      }
-    } else {
-      throw new TypeError(`Ilegal kind ${typeof name} for plugin name ${JSON.stringify(name)}`);
-    }
-
-    // validate position
-    if (position !== "before" && position !== "after") {
-      throw new TypeError(`Plugin ${JSON.stringify(name)} has an illegal position of ${JSON.stringify(position)}`);
-    }
-
-    // validate transformer key
-    var key = plugin.key;
-    if (this.transformers[key]) {
-      throw new ReferenceError(`The key for plugin ${JSON.stringify(name)} of ${key} collides with an existing plugin`);
-    }
-
-    // validate Transformer instance
-    if (!plugin.buildPass || plugin.constructor.name !== "Transformer") {
-      throw new TypeError(`Plugin ${JSON.stringify(name)} didn't export a default Transformer instance`);
-    }
-
-    // build!
-    var pass = this.transformers[key] = plugin.buildPass(this);
-    if (pass.canTransform()) {
-      var stack = before;
-      if (position === "after") stack = after;
-      stack.push(pass);
-    }
-  }
-
   parseInputSourceMap(code: string) {
     var opts = this.opts;
 
@@ -348,7 +305,7 @@ export default class File {
   }
 
   addImport(source: string, name?: string, type?: string): Object {
-    name ||= source;
+    name = name || source;
     var id = this.dynamicImportIds[name];
 
     if (!id) {
@@ -360,7 +317,7 @@ export default class File {
       declar._blockHoist = 3;
 
       if (type) {
-        var modules = this.dynamicImportTypes[type] ||= [];
+        var modules = this.dynamicImportTypes[type] = this.dynamicImportTypes[type] || [];
         modules.push(declar);
       }
 
@@ -375,14 +332,10 @@ export default class File {
     return id;
   }
 
-  isConsequenceExpressionStatement(node: Object): boolean {
-    return t.isExpressionStatement(node) && this.lastStatements.indexOf(node) >= 0;
-  }
-
   attachAuxiliaryComment(node: Object): Object {
     var comment = this.opts.auxiliaryComment;
     if (comment) {
-      node.leadingComments ||= [];
+      node.leadingComments = node.leadingComments || [];
       node.leadingComments.push({
         type: "Line",
         value: " " + comment
@@ -400,8 +353,8 @@ export default class File {
 
     var program = this.ast.program;
 
-    var declar = program._declarations && program._declarations[name];
-    if (declar) return declar.id;
+    var declar = this.declarations[name];
+    if (declar) return declar;
 
     this.usedHelpers[name] = true;
 
@@ -418,11 +371,11 @@ export default class File {
 
     var ref = util.template("helper-" + name);
     ref._compact = true;
-    var uid = this.scope.generateUidIdentifier(name);
+    var uid = this.declarations[name] = this.scope.generateUidIdentifier(name);
     this.scope.push({
-      key: name,
       id: uid,
-      init: ref
+      init: ref,
+      unique: true
     });
     return uid;
   }
@@ -479,9 +432,12 @@ export default class File {
     parseOpts.strictMode = features.strict;
     parseOpts.sourceType = "module";
 
+    this.log.debug("Parse start");
+
     //
 
     return parse(parseOpts, code, (tree) => {
+      this.log.debug("Parse stop");
       this.transform(tree);
       return this.generate();
     });
@@ -504,25 +460,25 @@ export default class File {
   }
 
   transform(ast) {
-    this.log.debug();
-
+    this.log.debug("Start set AST");
     this.setAst(ast);
+    this.log.debug("End set AST");
 
-    this.lastStatements = t.getLastStatements(ast.program);
+    this.log.debug("Start prepass");
+    this.checkPath(this.path);
+    this.log.debug("End prepass");
 
+    this.log.debug("Start module formatter init");
     var modFormatter = this.moduleFormatter = this.getModuleFormatter(this.opts.modules);
     if (modFormatter.init && this.transformers["es6.modules"].canTransform()) {
       modFormatter.init();
     }
-
-    this.checkNode(ast);
+    this.log.debug("End module formatter init");
 
     this.call("pre");
-
     each(this.transformerStack, function (pass) {
       pass.transform();
     });
-
     this.call("post");
   }
 
@@ -535,20 +491,19 @@ export default class File {
     }
   }
 
-  checkNode(node, scope) {
-    if (Array.isArray(node)) {
-      for (var i = 0; i < node.length; i++) {
-        this.checkNode(node[i], scope);
+  checkPath(path) {
+    if (Array.isArray(path)) {
+      for (var i = 0; i < path.length; i++) {
+        this.checkPath(path[i]);
       }
       return;
     }
 
     var stack = this.transformerStack;
-    scope ||= this.scope;
 
-    checkNode(stack, node, scope);
+    checkPath(stack, path);
 
-    scope.traverse(node, checkTransformerVisitor, {
+    path.traverse(checkTransformerVisitor, {
       stack: stack
     });
   }
@@ -598,10 +553,14 @@ export default class File {
     if (opts.ast) result.ast = ast;
     if (!opts.code) return result;
 
+    this.log.debug("Generation start");
+
     var _result = generate(ast, opts, this.code);
     result.code = _result.code;
     result.map  = _result.map;
 
+    this.log.debug("Generation end");
+
     if (this.shebang) {
       // add back shebang
       result.code = `${this.shebang}\n${result.code}`;

src/babel/transformation/file/option-parsers.js

@@ -1,14 +1,13 @@
-import transform from "./../index";
 import * as util from  "../../util";
 
-export function transformerList(key, val) {
+export function transformerList(key, val, pipeline) {
   val = util.arrayify(val);
 
   if (val.indexOf("all") >= 0 || val.indexOf(true) >= 0) {
-    val = Object.keys(transform.transformers);
+    val = Object.keys(pipeline.transformers);
   }
 
-  return transform._ensureTransformerNames(key, val);
+  return pipeline._ensureTransformerNames(key, val);
 }
 
 export function number(key, val) {

src/babel/transformation/file/options.json

@@ -25,6 +25,13 @@
     "type": "string"
   },
 
+  "retainLines": {
+    "hidden": true,
+    "type": "boolean",
+    "default": false,
+    "description": "retain line numbers - will result in really ugly code"
+  },
+
   "nonStandard": {
     "type": "boolean",
     "default": true,
@@ -212,5 +219,4 @@
     "hidden": true,
     "description": "do not load the same .babelrc file twice"
   }
-
 }

src/babel/transformation/file/plugin-manager.js

@@ -0,0 +1,105 @@
+import * as node from  "../../api/node";
+import * as messages from "../../messages";
+import * as util from  "../../util";
+
+export default class PluginManager {
+  static memoisedPlugins = [];
+
+  static memoisePluginContainer(fn) {
+    for (var i = 0; i < PluginManager.memoisedPlugins.length; i++) {
+      var plugin = PluginManager.memoisedPlugins[i];
+      if (plugin.container === fn) return plugin.transformer;
+    }
+
+    var transformer = fn(node);
+    PluginManager.memoisedPlugins.push({
+      container: fn,
+      transformer: transformer
+    });
+    return transformer;
+  }
+
+  static positions = ["before", "after"];
+
+  constructor({ file, transformers, before, after } = { transformers: {}, before: [], after: [] }) {
+    this.transformers = transformers;
+    this.file         = file;
+    this.before       = before;
+    this.after        = after;
+  }
+
+  subnormaliseString(name, position) {
+    // this is a plugin in the form of "foobar" or "foobar:after"
+    // where the optional colon is the delimiter for plugin position in the transformer stack
+
+    var match = name.match(/^(.*?):(after|before)$/);
+    if (match) [, name, position] = match;
+
+    var loc = util.resolveRelative(name) || util.resolveRelative(`babel-plugin-${name}`);
+    if (loc) {
+      return {
+        position: position,
+        plugin:   require(loc)
+      };
+    } else {
+      throw new ReferenceError(messages.get("pluginUnknown", name));
+    }
+  }
+
+  validate(name, plugin) {
+    // validate transformer key
+    var key = plugin.key;
+    if (this.transformers[key]) {
+      throw new ReferenceError(messages.get("pluginKeyCollision", key));
+    }
+
+    // validate Transformer instance
+    if (!plugin.buildPass || plugin.constructor.name !== "Transformer") {
+      throw new TypeError(messages.get("pluginNotTransformer", name));
+    }
+  }
+
+  add(name) {
+    var position;
+    var plugin;
+
+    if (name) {
+      if (typeof name === "object" && name.transformer) {
+        ({ plugin: name, position } = name);
+      } else if (typeof name !== "string") {
+        // not a string so we'll just assume that it's a direct Transformer instance, if not then
+        // the checks later on will complain
+        plugin = name;
+      }
+
+      if (typeof name === "string") {
+        ({ plugin, position } = this.subnormaliseString(name, position));
+      }
+    } else {
+      throw new TypeError(messages.get("pluginIllegalKind", typeof name, name));
+    }
+
+    // default position
+    position = position || "before";
+
+    // validate position
+    if (PluginManager.positions.indexOf(position) < 0) {
+      throw new TypeError(messages.get("pluginIllegalPosition", position, name));
+    }
+
+    // allow plugin containers to be specified so they don't have to manually require
+    if (typeof plugin === "function") {
+      plugin = PluginManager.memoisePluginContainer(plugin);
+    }
+
+    //
+    this.validate(name, plugin);
+
+    // build!
+    var pass = this.transformers[plugin.key] = plugin.buildPass(this.file);
+    if (pass.canTransform()) {
+      var stack = position === "before" ? this.before : this.after;
+      stack.push(pass);
+    }
+  }
+}

src/babel/transformation/helpers/build-binary-assignment-operator-transformer.js

@@ -10,9 +10,13 @@ export default function (exports, opts) {
     return t.assignmentExpression("=", left, right);
   };
 
+  exports.shouldVisit = function (node) {
+    return node.operator && (node.operator === opts.operator || node.operator === opts.operator + "=");
+  };
+
   exports.ExpressionStatement = function (node, parent, scope, file) {
     // hit the `AssignmentExpression` one below
-    if (file.isConsequenceExpressionStatement(node)) return;
+    if (this.isCompletionRecord()) return;
 
     var expr = node.expression;
     if (!isAssignment(expr)) return;

src/babel/transformation/helpers/build-conditional-assignment-operator-transformer.js

@@ -8,7 +8,7 @@ export default function (exports, opts) {
 
   exports.ExpressionStatement = function (node, parent, scope, file) {
     // hit the `AssignmentExpression` one below
-    if (file.isConsequenceExpressionStatement(node)) return;
+    if (this.isCompletionRecord()) return;
 
     var expr = node.expression;
     if (!opts.is(expr, file)) return;

src/babel/transformation/helpers/define-map.js

@@ -15,7 +15,7 @@ export function push(mutatorMap, node, kind, file) {
 
   //
 
-  map._inherits ||= [];
+  map._inherits = map._inherits || [];
   map._inherits.push(node);
 
   map._key = node.key;
@@ -25,7 +25,7 @@ export function push(mutatorMap, node, kind, file) {
   }
 
   if (node.decorators) {
-    var decorators = map.decorators ||= t.arrayExpression([]);
+    var decorators = map.decorators = map.decorators || t.arrayExpression([]);
     decorators.elements = decorators.elements.concat(node.decorators.map(dec => dec.expression));
   }
 

src/babel/transformation/helpers/memoise-decorators.js

@@ -26,7 +26,11 @@ export default function (decorators, scope) {
       [ref]
     ));
 
-    decorator.expression = t.sequenceExpression(nodes);
+    if (nodes.length === 1) {
+      decorator.expression = nodes[0];
+    } else {
+      decorator.expression = t.sequenceExpression(nodes);
+    }
   }
 
   return decorators;

src/babel/transformation/helpers/name-method.js

@@ -20,27 +20,32 @@ var visitor = {
 
 var wrap = function (state, method, id, scope) {
   if (state.selfReference) {
-    var templateName = "property-method-assignment-wrapper";
-    if (method.generator) templateName += "-generator";
-    var template = util.template(templateName, {
-      FUNCTION: method,
-      FUNCTION_ID: id,
-      FUNCTION_KEY: scope.generateUidIdentifier(id.name)
-    });
-    template.callee._skipModulesRemap = true;
+    if (scope.hasBinding(id.name)) {
+      // we can just munge the local binding
+      scope.rename(id.name);
+    } else {
+      // need to add a wrapper since we can't change the references
+      var templateName = "property-method-assignment-wrapper";
+      if (method.generator) templateName += "-generator";
+      var template = util.template(templateName, {
+        FUNCTION: method,
+        FUNCTION_ID: id,
+        FUNCTION_KEY: scope.generateUidIdentifier(id.name)
+      });
+      template.callee._skipModulesRemap = true;
 
-    // shim in dummy params to retain function arity, if you try to read the
-    // source then you'll get the original since it's proxied so it's all good
-    var params = template.callee.body.body[0].params;
-    for (var i = 0, len = getFunctionArity(method); i < len; i++) {
-      params.push(scope.generateUidIdentifier("x"));
+      // shim in dummy params to retain function arity, if you try to read the
+      // source then you'll get the original since it's proxied so it's all good
+      var params = template.callee.body.body[0].params;
+      for (var i = 0, len = getFunctionArity(method); i < len; i++) {
+        params.push(scope.generateUidIdentifier("x"));
+      }
+
+      return template;
     }
-
-    return template;
-  } else {
-    method.id = id;
-    return method;
   }
+
+  method.id = id;
 };
 
 var visit = function (node, name, scope) {
@@ -82,7 +87,7 @@ var visit = function (node, name, scope) {
       // so we can safely just set the id and move along as it shadows the
       // bound function id
     }
-  } else {
+  } else if (state.outerDeclar || scope.hasGlobal(name)) {
     scope.traverse(node, visitor, state);
   }
 
@@ -96,7 +101,7 @@ export function custom(node, id, scope) {
 
 export function property(node, file, scope) {
   var key = t.toComputedKey(node, node.key);
-  if (!t.isLiteral(key)) return node; // we can't set a function id with this
+  if (!t.isLiteral(key)) return; // we can't set a function id with this
 
   var name = t.toIdentifier(key.value);
   if (name === "eval" || name === "arguments") name = "_" + name;
@@ -104,12 +109,12 @@ export function property(node, file, scope) {
 
   var method = node.value;
   var state  = visit(method, name, scope);
-  node.value = wrap(state, method, id, scope);
+  node.value = wrap(state, method, id, scope) || method;
 }
 
 export function bare(node, parent, scope) {
   // has an `id` so we don't need to infer one
-  if (node.id) return node;
+  if (node.id) return;
 
   var id;
   if (t.isProperty(parent) && parent.kind === "init" && (!parent.computed || t.isLiteral(parent.key))) {
@@ -118,8 +123,17 @@ export function bare(node, parent, scope) {
   } else if (t.isVariableDeclarator(parent)) {
     // var foo = function () {};
     id = parent.id;
+
+    if (t.isIdentifier(id)) {
+      var bindingInfo = scope.parent.getBinding(id.name);
+      if (bindingInfo && bindingInfo.constant && scope.getBinding(id.name) === bindingInfo) {
+        // always going to reference this method
+        node.id = id;
+        return;
+      }
+    }
   } else {
-    return node;
+    return;
   }
 
   var name;

src/babel/transformation/helpers/remap-async-to-generator.js

@@ -20,7 +20,7 @@ var referenceVisitor = {
   enter(node, parent, scope, state) {
     var name = state.id.name;
     if (t.isReferencedIdentifier(node, parent, { name: name }) && scope.bindingIdentifierEquals(name, state.id)) {
-      return state.ref ||= scope.generateUidIdentifier(name);
+      return state.ref = state.ref || scope.generateUidIdentifier(name);
     }
   }
 };

src/babel/transformation/helpers/replace-supers.js

@@ -218,7 +218,7 @@ export default class ReplaceSupers {
       return this.setSuperProperty(node.left.property, node.right, node.left.computed, getThisReference());
     } else {
       // super.age += 2; -> var _ref = super.age; super.age = _ref + 2;
-      ref ||= path.scope.generateUidIdentifier("ref");
+      ref = ref || path.scope.generateUidIdentifier("ref");
       return [
         t.variableDeclaration("var", [
           t.variableDeclarator(ref, node.left)

src/babel/transformation/index.js

@@ -1,68 +1,34 @@
-import normalizeAst from "../helpers/normalize-ast";
-import Transformer from "./transformer";
-import object from "../helpers/object";
-import File from "./file";
-import each from "lodash/collection/each";
+import Pipeline from "./transformer-pipeline";
 
-export default function transform(code: string, opts?: Object) {
-  var file = new File(opts);
-  return file.parse(code);
-}
+var pipeline = new Pipeline;
 
-transform.fromAst = function (ast, code, opts) {
-  ast = normalizeAst(ast);
+//
 
-  var file = new File(opts);
-  file.addCode(code);
-  file.transform(ast);
-  return file.generate();
-};
+import transformers from "./transformers";
+pipeline.addTransformers(transformers);
 
-transform._ensureTransformerNames = function (type: string, rawKeys: Array<string>) {
-  var keys = [];
+//
 
-  for (var i = 0; i < rawKeys.length; i++) {
-    var key = rawKeys[i];
+import deprecated from "./transformers/deprecated";
+pipeline.addDeprecated(deprecated);
 
-    var deprecatedKey = transform.deprecatedTransformerMap[key];
-    var aliasKey = transform.aliasTransformerMap[key];
-    if (aliasKey) {
-      keys.push(aliasKey);
-    } else if (deprecatedKey) {
-      // deprecated key, remap it to the new one
-      console.error(`The transformer ${key} has been renamed to ${deprecatedKey}`);
-      rawKeys.push(deprecatedKey);
-    } else if (transform.transformers[key]) {
-      // valid key
-      keys.push(key);
-    } else if (transform.namespaces[key]) {
-      // namespace, append all transformers within this namespace
-      keys = keys.concat(transform.namespaces[key]);
-    } else {
-      // invalid key
-      throw new ReferenceError(`Unknown transformer ${key} specified in ${type}`);
-    }
-  }
+//
 
-  return keys;
-};
+import aliases from "./transformers/aliases";
+pipeline.addDeprecated(aliases);
 
-transform.transformerNamespaces = object();
-transform.transformers          = object();
-transform.namespaces            = object();
+//
 
-transform.deprecatedTransformerMap = require("./transformers/deprecated");
-transform.aliasTransformerMap = require("./transformers/aliases");
-transform.moduleFormatters = require("./modules");
+import * as filters from "./transformers/filters";
+pipeline.addFilter(filters.internal);
+pipeline.addFilter(filters.blacklist);
+pipeline.addFilter(filters.whitelist);
+pipeline.addFilter(filters.stage);
+pipeline.addFilter(filters.optional);
 
-import rawTransformers from "./transformers";
+//
 
-each(rawTransformers, function (transformer, key) {
-  var namespace = key.split(".")[0];
-
-  transform.namespaces[namespace] ||= [];
-  transform.namespaces[namespace].push(key);
-  transform.transformerNamespaces[key] = namespace;
-
-  transform.transformers[key] = new Transformer(key, transformer);
-});
+var transform = pipeline.transform.bind(pipeline);
+transform.fromAst = pipeline.transformFromAst.bind(pipeline);
+transform.pipeline = pipeline;
+export default transform;

src/babel/transformation/modules/_default.js

@@ -166,7 +166,7 @@ export default class DefaultFormatter {
   }
 
   _addExport(name, exported) {
-    var info = this.localExports[name] ||= {
+    var info = this.localExports[name] = this.localExports[name] || {
       binding: this.scope.getBindingIdentifier(name),
       exported: []
     };

src/babel/transformation/modules/common.js

@@ -20,7 +20,7 @@ export default class CommonJSFormatter extends DefaultFormatter {
       if (this.file.isLoose("es6.modules")) templateName += "-loose";
       var declar = util.template(templateName, true);
       declar._blockHoist = 3;
-      file.ast.program.body.unshift(declar);
+      file.path.unshiftContainer("body", [declar]);
     }
   }
 
@@ -114,7 +114,7 @@ export default class CommonJSFormatter extends DefaultFormatter {
       uid = this.scope.generateUidBasedOnNode(node, "import");
     }
 
-    uid ||= node.specifiers[0].local;
+    uid = uid || node.specifiers[0].local;
 
     var declar = t.variableDeclaration("var", [
       t.variableDeclarator(uid, call)

src/babel/transformation/modules/system.js

@@ -77,11 +77,11 @@ var runnerSettersVisitor = {
 
 export default class SystemFormatter extends AMDFormatter {
   constructor(file) {
+    super(file);
+
     this.exportIdentifier = file.scope.generateUidIdentifier("export");
     this.noInteropRequireExport = true;
     this.noInteropRequireImport = true;
-
-    DefaultFormatter.apply(this, arguments);
   }
 
   _addImportSource(node, exportNode) {

src/babel/transformation/templates/helper-create-decorated-class.js

@@ -24,7 +24,7 @@
           }
         }
 
-        if (descriptor.initializer) {
+        if (descriptor.initializer !== undefined) {
           initializers[key] = descriptor;
           continue;
         }

src/babel/transformation/templates/helper-create-decorated-object.js

@@ -26,9 +26,10 @@
       }
     }
 
-    descriptor.value = descriptor.initializer();
-
-    Object.defineProperty(target, key, descriptor);
+    if (descriptor.initializer) {
+      descriptor.value = descriptor.initializer.call(target);
+      Object.defineProperty(target, key, descriptor);
+    }
   }
 
   return target;

src/babel/transformation/templates/helper-define-decorated-property-descriptor.js

@@ -6,7 +6,8 @@
   for (var _key in _descriptor) descriptor[_key] = _descriptor[_key];
 
   // initialize it
-  descriptor.value = descriptor.initializer();
+  if (!descriptor.initializer) return;
+  descriptor.value = descriptor.initializer.call(target);
 
   Object.defineProperty(target, key, descriptor);
 })

src/babel/transformation/templates/helper-instanceof.js

@@ -0,0 +1,7 @@
+(function (left, right) {
+  if (right != null && right[Symbol.hasInstance]) {
+    return right[Symbol.hasInstance](left);
+  } else {
+    return left instanceof right;
+  }
+});

src/babel/transformation/templates/helper-interop-require-wildcard.js

@@ -3,7 +3,7 @@
     return obj;
   } else {
     var newObj = {};
-    if (typeof obj === "object" && obj !== null) {
+    if (obj != null) {
       for (var key in obj) {
         if (Object.prototype.hasOwnProperty.call(obj, key)) newObj[key] = obj[key];
       }

src/babel/transformation/transformer-pass.js

@@ -8,58 +8,35 @@ import traverse from "../traversal";
 
 export default class TransformerPass {
   constructor(file: File, transformer: Transformer) {
-    this.transformer = transformer;
-    this.shouldRun   = !transformer.check;
-    this.handlers    = transformer.handlers;
-    this.file        = file;
-    this.ran         = false;
+    this.shouldTransform = !transformer.shouldVisit;
+    this.transformer     = transformer;
+    this.handlers        = transformer.handlers;
+    this.skipKey         = transformer.skipKey;
+    this.file            = file;
+    this.ran             = false;
   }
 
   canTransform(): boolean {
-    var transformer = this.transformer;
-
-    var opts = this.file.opts;
-    var key  = transformer.key;
-
-    // internal
-    if (key[0] === "_") return true;
-
-    // blacklist
-    var blacklist = opts.blacklist;
-    if (blacklist.length && includes(blacklist, key)) return false;
-
-    // whitelist
-    var whitelist = opts.whitelist;
-    if (whitelist) return includes(whitelist, key);
-
-    // stage
-    var stage = transformer.metadata.stage;
-    if (stage != null && stage >= opts.stage) return true;
-
-    // optional
-    if (transformer.metadata.optional && !includes(opts.optional, key)) return false;
-
-    return true;
+    return this.file.pipeline.canTransform(this.transformer, this.file.opts);
   }
 
-  checkNode(node: Object): boolean {
-    var check = this.transformer.check;
-    if (check) {
-      return this.shouldRun = check(node);
-    } else {
-      return true;
-    }
+  checkPath(path: TraversalPath): boolean {
+    if (this.shouldTransform || this.ran) return;
+
+    this.shouldTransform = this.transformer.shouldVisit(path.node);
   }
 
   transform() {
-    if (!this.shouldRun) return;
+    if (!this.shouldTransform) return;
 
     var file = this.file;
 
-    file.log.debug(`Running transformer ${this.transformer.key}`);
+    file.log.debug(`Start transformer ${this.transformer.key}`);
 
     traverse(file.ast, this.handlers, file.scope, file);
 
+    file.log.debug(`Finish transformer ${this.transformer.key}`);
+
     this.ran = true;
   }
 }

src/babel/transformation/transformer-pipeline.js

@@ -0,0 +1,100 @@
+import Transformer from "./transformer";
+import normalizeAst from "../helpers/normalize-ast";
+import assign from "lodash/object/assign";
+import object from "../helpers/object";
+import File from "./file";
+
+export default class TransformerPipeline {
+  constructor() {
+    this.transformers = object();
+    this.namespaces   = object();
+    this.deprecated   = object();
+    this.aliases      = object();
+    this.filters      = [];
+  }
+
+  addTransformers(transformers) {
+    for (var key in transformers) {
+      this.addTransformer(key, transformers[key]);
+    }
+    return this;
+  }
+
+  addTransformer(key, transformer) {
+    if (this.transformers[key]) throw new Error(); // todo: error
+
+    var namespace = key.split(".")[0];
+    this.namespaces[namespace] = this.namespaces[namespace] || [];
+    this.namespaces[namespace].push(key);
+    this.namespaces[key] = namespace;
+
+    this.transformers[key] = new Transformer(key, transformer);
+  }
+
+  addAliases(names) {
+    assign(this.aliases, names);
+    return this;
+  }
+
+  addDeprecated(names) {
+    assign(this.deprecated, names);
+    return this;
+  }
+
+  addFilter(filter: Function) {
+    this.filters.push(filter);
+    return this;
+  }
+
+  canTransform(transformer, fileOpts) {
+    for (var filter of (this.filters: Array)) {
+      var result = filter(transformer, fileOpts);
+      if (result != null) return result;
+    }
+
+    return true;
+  }
+
+  transform(code: string, opts?: Object) {
+    var file = new File(opts, this);
+    return file.parse(code);
+  }
+
+  transformFromAst(ast, code, opts) {
+    ast = normalizeAst(ast);
+
+    var file = new File(opts, this);
+    file.addCode(code);
+    file.transform(ast);
+    return file.generate();
+  }
+
+  _ensureTransformerNames(type: string, rawKeys: Array<string>) {
+    var keys = [];
+
+    for (var i = 0; i < rawKeys.length; i++) {
+      var key = rawKeys[i];
+
+      var deprecatedKey = this.deprecated[key];
+      var aliasKey = this.aliases[key];
+      if (aliasKey) {
+        keys.push(aliasKey);
+      } else if (deprecatedKey) {
+        // deprecated key, remap it to the new one
+        console.error(`The transformer ${key} has been renamed to ${deprecatedKey}`);
+        rawKeys.push(deprecatedKey);
+      } else if (this.transformers[key]) {
+        // valid key
+        keys.push(key);
+      } else if (this.namespaces[key]) {
+        // namespace, append all transformers within this namespace
+        keys = keys.concat(this.namespaces[key]);
+      } else {
+        // invalid key
+        throw new ReferenceError(`Unknown transformer ${key} specified in ${type}`);
+      }
+    }
+
+    return keys;
+  }
+}

src/babel/transformation/transformer.js

@@ -1,4 +1,5 @@
 import TransformerPass from "./transformer-pass";
+import * as messages from "../messages";
 import isFunction from "lodash/lang/isFunction";
 import traverse from "../traversal";
 import isObject from "lodash/lang/isObject";
@@ -14,7 +15,7 @@ import each from "lodash/collection/each";
  */
 
 export default class Transformer {
-  constructor(transformerKey: key, transformer: Object, opts: Object) {
+  constructor(transformerKey: string, transformer: Object) {
     transformer = assign({}, transformer);
 
     var take = function (key) {
@@ -24,19 +25,34 @@ export default class Transformer {
     };
 
     this.manipulateOptions = take("manipulateOptions");
+    this.shouldVisit       = take("shouldVisit");
     this.metadata          = take("metadata") || {};
     this.parser            = take("parser");
-    this.check             = take("check");
     this.post              = take("post");
     this.pre               = take("pre");
 
+    //
+
     if (this.metadata.stage != null) {
       this.metadata.optional = true;
     }
 
+    //
+
     this.handlers = this.normalize(transformer);
-    this.opts     ||= {};
     this.key      = transformerKey;
+
+    //
+
+    if (!this.shouldVisit) {
+      var types = Object.keys(this.handlers);
+      this.shouldVisit = function (node) {
+        for (var i = 0; i < types.length; i++) {
+          if (node.type === types[i]) return true;
+        }
+        return false;
+      };
+    }
   }
 
   normalize(transformer: Object): Object {
@@ -71,7 +87,7 @@ export default class Transformer {
   buildPass(file: File): TransformerPass {
     // validate Transformer instance
     if (!(file instanceof File)) {
-      throw new TypeError(`Transformer ${this.key} is resolving to a different Babel version to what is doing the actual transformation...`);
+      throw new TypeError(messages.get("transformerNotFile", this.key));
     }
 
     return new TransformerPass(file, this);

src/babel/transformation/transformers/es5/properties.mutators.js

@@ -1,7 +1,7 @@
 import * as defineMap from "../../helpers/define-map";
 import * as t from "../../../types";
 
-export function check(node) {
+export function shouldVisit(node) {
   return t.isProperty(node) && (node.kind === "get" || node.kind === "set");
 }
 

src/babel/transformation/transformers/es6/arrow-functions.js

@@ -1,6 +1,6 @@
 import * as t from "../../../types";
 
-export var check = t.isArrowFunctionExpression;
+export var shouldVisit = t.isArrowFunctionExpression;
 
 export function ArrowFunctionExpression(node) {
   t.ensureBlock(node);

src/babel/transformation/transformers/es6/block-scoping.js

@@ -14,7 +14,7 @@ function isLet(node, parent) {
   if (isLetInitable(node, parent)) {
     for (var i = 0; i < node.declarations.length; i++) {
       var declar = node.declarations[i];
-      declar.init ||= t.identifier("undefined");
+      declar.init = declar.init || t.identifier("undefined");
     }
   }
 
@@ -37,7 +37,7 @@ function standardizeLets(declars) {
   }
 }
 
-export function check(node) {
+export function shouldVisit(node) {
   return t.isVariableDeclaration(node) && (node.kind === "let" || node.kind === "const");
 }
 
@@ -139,7 +139,12 @@ var hoistVarDeclarationsVisitor = {
   enter(node, parent, scope, self) {
     if (this.isForStatement()) {
       if (isVar(node.init, node)) {
-        node.init = t.sequenceExpression(self.pushDeclar(node.init));
+        var nodes = self.pushDeclar(node.init);
+        if (nodes.length === 1) {
+          node.init = nodes[0];
+        } else {
+          node.init = t.sequenceExpression(nodes);
+        }
       }
     } else if (this.isFor()) {
       if (isVar(node.left, node)) {
@@ -606,7 +611,7 @@ class BlockScoping {
         for (var i = 0; i < cases.length; i++) {
           var caseConsequent = cases[i].consequent[0];
           if (t.isBreakStatement(caseConsequent) && !caseConsequent.label) {
-            caseConsequent.label = this.loopLabel ||= this.file.scope.generateUidIdentifier("loop");
+            caseConsequent.label = this.loopLabel = this.loopLabel || this.file.scope.generateUidIdentifier("loop");
           }
         }
 

src/babel/transformation/transformers/es6/classes.js

@@ -11,7 +11,7 @@ import * as t from "../../../types";
 
 const PROPERTY_COLLISION_METHOD_NAME = "__initializeProperties";
 
-export var check = t.isClass;
+export var shouldVisit = t.isClass;
 
 export function ClassDeclaration(node, parent, scope, file) {
   return t.variableDeclaration("let", [
@@ -245,7 +245,7 @@ class ClassTransformer {
       if (body.length === 1) return t.toExpression(body[0]);
     } else {
       // infer class name if this is a nameless class expression
-      constructor = nameMethod.bare(constructor, this.parent, this.scope);
+      constructor = nameMethod.bare(constructor, this.parent, this.scope) || constructor;
 
       body.unshift(t.variableDeclaration("var", [
         t.variableDeclarator(classRef, constructor)
@@ -347,7 +347,7 @@ class ClassTransformer {
       if (this.isNativeSuper) helperName = "class-super-native-constructor-call";
       constructorBody.body.push(util.template(helperName, {
         NATIVE_REF: this.nativeSuperRef,
-        CLASS_NAME: className,
+        CLASS_NAME: this.classRef,
         SUPER_NAME: this.superName
       }, true));
     }
@@ -550,19 +550,23 @@ class ClassTransformer {
 
     if (node.decorators) {
       var body = [];
-      if (node.value) body.push(t.returnStatement(node.value));
-      node.value = t.functionExpression(null, [], t.blockStatement(body));
+      if (node.value) {
+        body.push(t.returnStatement(node.value));
+        node.value = t.functionExpression(null, [], t.blockStatement(body));
+      } else {
+        node.value = t.literal(null);
+      }
       this.pushToMap(node, true, "initializer");
 
       var initializers;
       var body;
       var target;
       if (node.static) {
-        initializers = this.staticInitializersId ||= this.scope.generateUidIdentifier("staticInitializers");
+        initializers = this.staticInitializersId = this.staticInitializersId || this.scope.generateUidIdentifier("staticInitializers");
         body = this.staticPropBody;
         target = this.classRef;
       } else {
-        initializers = this.instanceInitializersId ||= this.scope.generateUidIdentifier("instanceInitializers");
+        initializers = this.instanceInitializersId = this.instanceInitializersId || this.scope.generateUidIdentifier("instanceInitializers");
         body = this.instancePropBody;
         target = t.thisExpression();
       }
@@ -575,7 +579,7 @@ class ClassTransformer {
         ])
       ));
     } else {
-      node.value ||= t.identifier("undefined");
+      if (!node.value && !node.decorators) return;
 
       if (node.static) {
         // can just be added to the static map

src/babel/transformation/transformers/es6/constants.js

@@ -1,7 +1,7 @@
 import * as messages from "../../../messages";
 import * as t from "../../../types";
 
-export function check(node) {
+export function shouldVisit(node) {
   return t.isVariableDeclaration(node, { kind: "const" }) || t.isImportDeclaration(node);
 }
 

src/babel/transformation/transformers/es6/destructuring.js

@@ -1,7 +1,7 @@
 import * as messages from "../../../messages";
 import * as t from "../../../types";
 
-export var check = t.isPattern;
+export var shouldVisit = t.isPattern;
 
 export function ForOfStatement(node, parent, scope, file) {
   var left = node.left;
@@ -78,11 +78,11 @@ exports.Function = function (node, parent, scope, file) {
 
   if (!hasDestructuring) return;
 
-  file.checkNode(nodes);
   t.ensureBlock(node);
 
   var block = node.body;
   block.body = nodes.concat(block.body);
+  return node;
 };
 
 export function CatchClause(node, parent, scope, file) {
@@ -111,7 +111,7 @@ export function ExpressionStatement(node, parent, scope, file) {
   var expr = node.expression;
   if (expr.type !== "AssignmentExpression") return;
   if (!t.isPattern(expr.left)) return;
-  if (file.isConsequenceExpressionStatement(node)) return;
+  if (this.isCompletionRecord()) return;
 
   var destructuring = new DestructuringTransformer({
     operator: expr.operator,
@@ -200,7 +200,7 @@ export function VariableDeclaration(node, parent, scope, file) {
 
     for (i = 0; i < nodes.length; i++) {
       node = nodes[i];
-      declar ||= t.variableDeclaration(node.kind, []);
+      declar = declar || t.variableDeclaration(node.kind, []);
 
       if (!t.isVariableDeclaration(node) && declar.kind !== node.kind) {
         throw file.errorWithNode(node, messages.get("invalidParentForThisNode"));

src/babel/transformation/transformers/es6/for-of.js

@@ -2,7 +2,7 @@ import * as messages from "../../../messages";
 import * as util from  "../../../util";
 import * as t from "../../../types";
 
-export var check = t.isForOfStatement;
+export var shouldVisit = t.isForOfStatement;
 
 export function ForOfStatement(node, parent, scope, file) {
   if (this.get("right").isArrayExpression()) {

src/babel/transformation/transformers/es6/object-super.js

@@ -1,7 +1,7 @@
 import ReplaceSupers from "../../helpers/replace-supers";
 import * as t from "../../../types";
 
-export var check = t.isSuper;
+export var shouldVisit = t.isSuper;
 
 function Property(path, node, scope, getObjectRef, file) {
   if (!node.method) return;
@@ -32,7 +32,7 @@ function Property(path, node, scope, getObjectRef, file) {
 
 export function ObjectExpression(node, parent, scope, file) {
   var objectRef;
-  var getObjectRef = () => objectRef ||= scope.generateUidIdentifier("obj");
+  var getObjectRef = () => objectRef = objectRef || scope.generateUidIdentifier("obj");
 
   var propPaths = this.get("properties");
   for (var i = 0; i < node.properties.length; i++) {

src/babel/transformation/transformers/es6/parameters.default.js

@@ -2,7 +2,7 @@ import callDelegate from "../../helpers/call-delegate";
 import * as util from  "../../../util";
 import * as t from "../../../types";
 
-export function check(node) {
+export function shouldVisit(node) {
   return t.isFunction(node) && hasDefaults(node);
 }
 
@@ -45,7 +45,6 @@ exports.Function = function (node, parent, scope, file) {
       ARGUMENT_KEY:  t.literal(i),
       ARGUMENTS:     argsIdentifier
     }, true);
-    file.checkNode(defNode);
     defNode._blockHoist = node.params.length - i;
     body.push(defNode);
   };
@@ -97,4 +96,6 @@ exports.Function = function (node, parent, scope, file) {
   } else {
     node.body.body = body.concat(node.body.body);
   }
+
+  return node;
 };

src/babel/transformation/transformers/es6/parameters.rest.js

@@ -2,7 +2,7 @@ import isNumber from "lodash/lang/isNumber";
 import * as util from  "../../../util";
 import * as t from "../../../types";
 
-export var check = t.isRestElement;
+export var shouldVisit = t.isRestElement;
 
 var memberExpressionOptimisationVisitor = {
   enter(node, parent, scope, state) {
@@ -74,7 +74,6 @@ exports.Function = function (node, parent, scope, file) {
       var accessExpr = t.memberExpression(rest, t.literal(index), true);
       return t.variableDeclarator(elem, accessExpr);
     }));
-    file.checkNode(declar);
     node.body.body.unshift(declar);
   }
 
@@ -97,7 +96,7 @@ exports.Function = function (node, parent, scope, file) {
       candidate.replaceWith(argsId);
       optimizeMemberExpression(candidate.parent, node.params.length);
     }
-    return;
+    return node;
   }
 
   //
@@ -138,4 +137,5 @@ exports.Function = function (node, parent, scope, file) {
   });
   loop._blockHoist = node.params.length + 1;
   node.body.body.unshift(loop);
+  return node;
 };

src/babel/transformation/transformers/es6/properties.computed.js

@@ -84,7 +84,7 @@ function spec(node, body, objId, initProps, file) {
   }
 }
 
-export function check(node) {
+export function shouldVisit(node) {
   return t.isProperty(node) && node.computed;
 }
 

src/babel/transformation/transformers/es6/properties.shorthand.js

@@ -1,6 +1,6 @@
 import * as t from "../../../types";
 
-export function check(node) {
+export function shouldVisit(node) {
   return t.isProperty(node) && (node.method || node.shorthand);
 }
 

src/babel/transformation/transformers/es6/regex.sticky.js

@@ -1,7 +1,7 @@
 import * as regex from "../../helpers/regex";
 import * as t from "../../../types";
 
-export function check(node) {
+export function shouldVisit(node) {
   return regex.is(node, "y");
 }
 

src/babel/transformation/transformers/es6/regex.unicode.js

@@ -1,7 +1,7 @@
 import rewritePattern from "regexpu/rewrite-pattern";
 import * as regex from "../../helpers/regex";
 
-export function check(node) {
+export function shouldVisit(node) {
   return regex.is(node, "u");
 }
 

src/babel/transformation/transformers/es6/spec.symbols.js

@@ -5,14 +5,16 @@ export var metadata = {
 };
 
 export function UnaryExpression(node, parent, scope, file) {
-  this.skip();
+  if (node._ignoreSpecSymbols) return;
 
   if (node.operator === "typeof") {
     var call = t.callExpression(file.addHelper("typeof"), [node.argument]);
     if (this.get("argument").isIdentifier()) {
       var undefLiteral = t.literal("undefined");
+      var unary = t.unaryExpression("typeof", node.argument);
+      unary._ignoreSpecSymbols = true;
       return t.conditionalExpression(
-        t.binaryExpression("===", t.unaryExpression("typeof", node.argument), undefLiteral),
+        t.binaryExpression("===", unary, undefLiteral),
         undefLiteral,
         call
       );
@@ -21,3 +23,13 @@ export function UnaryExpression(node, parent, scope, file) {
     }
   }
 }
+
+export function BinaryExpression(node, parent, scope, file) {
+  if (node.operator === "instanceof") {
+    return t.callExpression(file.addHelper("instanceof"), [node.left, node.right]);
+  }
+}
+
+export function VariableDeclaration(node) {
+  if (node._generated) this.skip();
+}

src/babel/transformation/transformers/es6/spread.js

@@ -44,7 +44,7 @@ function build(props, scope) {
   return nodes;
 }
 
-export var check = t.isSpreadElement;
+export var shouldVisit = t.isSpreadElement;
 
 export function ArrayExpression(node, parent, scope) {
   var elements = node.elements;

src/babel/transformation/transformers/es6/tail-call.js

@@ -101,23 +101,23 @@ class TailCallTransformer {
   }
 
   getArgumentsId() {
-    return this.argumentsId ||= this.scope.generateUidIdentifier("arguments");
+    return this.argumentsId = this.argumentsId || this.scope.generateUidIdentifier("arguments");
   }
 
   getThisId() {
-    return this.thisId ||= this.scope.generateUidIdentifier("this");
+    return this.thisId = this.thisId || this.scope.generateUidIdentifier("this");
   }
 
   getLeftId() {
-    return this.leftId ||= this.scope.generateUidIdentifier("left");
+    return this.leftId = this.leftId || this.scope.generateUidIdentifier("left");
   }
 
   getFunctionId() {
-    return this.functionId ||= this.scope.generateUidIdentifier("function");
+    return this.functionId = this.functionId || this.scope.generateUidIdentifier("function");
   }
 
   getAgainId() {
-    return this.againId ||= this.scope.generateUidIdentifier("again");
+    return this.againId = this.againId || this.scope.generateUidIdentifier("again");
   }
 
   getParams() {

src/babel/transformation/transformers/es6/template-literals.js

@@ -4,7 +4,7 @@ var buildBinaryExpression = function (left, right) {
   return t.binaryExpression("+", left, right);
 };
 
-export function check(node) {
+export function shouldVisit(node) {
   return t.isTemplateLiteral(node) || t.isTaggedTemplateExpression(node);
 }
 

src/babel/transformation/transformers/es7/async-functions.js

@@ -2,6 +2,6 @@ export var metadata = {
   stage: 1
 };
 
-export function check() {
+export function shouldVisit() {
   return false;
 }

src/babel/transformation/transformers/es7/class-properties.js

@@ -2,6 +2,6 @@ export var metadata = {
   stage: 0
 };
 
-export function check() {
+export function shouldVisit() {
   return false;
 }

src/babel/transformation/transformers/es7/decorators.js

@@ -7,7 +7,7 @@ export var metadata = {
   stage: 1
 };
 
-export function check(node) {
+export function shouldVisit(node) {
   return !!node.decorators;
 }
 

src/babel/transformation/transformers/es7/do-expressions.js

@@ -5,7 +5,7 @@ export var metadata = {
   stage: 0
 };
 
-export var check = t.isDoExpression;
+export var shouldVisit = t.isDoExpression;
 
 export function DoExpression(node) {
   var body = node.body.body;

src/babel/transformation/transformers/es7/export-extensions.js

@@ -6,7 +6,7 @@ export var metadata = {
   stage: 1
 };
 
-export function check(node) {
+export function shouldVisit(node) {
   return t.isExportDefaultSpecifier(node) || t.isExportNamespaceSpecifier(node);
 }
 

src/babel/transformation/transformers/es7/trailing-function-commas.js

@@ -2,6 +2,6 @@ export var metadata = {
   stage: 1
 };
 
-export function check() {
+export function shouldVisit() {
   return false;
 }

src/babel/transformation/transformers/filters.js

@@ -0,0 +1,24 @@
+import includes from "lodash/collection/includes";
+
+export function internal(transformer, opts) {
+  if (transformer.key[0] === "_") return true;
+}
+
+export function blacklist(transformer, opts) {
+  var blacklist = opts.blacklist;
+  if (blacklist.length && includes(blacklist, transformer.key)) return false;
+}
+
+export function whitelist(transformer, opts) {
+  var whitelist = opts.whitelist;
+  if (whitelist) return includes(whitelist, transformer.key);
+}
+
+export function stage(transformer, opts) {
+  var stage = transformer.metadata.stage;
+  if (stage != null && stage >= opts.stage) return true;
+}
+
+export function optional(transformer, opts) {
+  if (transformer.metadata.optional && !includes(opts.optional, transformer.key)) return false;
+}

src/babel/transformation/transformers/index.js

@@ -1,4 +1,6 @@
 export default {
+  _modules:                                require("./internal/modules"),
+
   "es7.classProperties":                   require("./es7/class-properties"),
   "es7.trailingFunctionCommas":            require("./es7/trailing-function-commas"),
   "es7.asyncFunctions":                    require("./es7/async-functions"),
@@ -24,8 +26,6 @@ export default {
   reactCompat:                             require("./other/react-compat"),
   react:                                   require("./other/react"),
 
-  _modules:                                require("./internal/modules"),
-
   // needs to be before `regenerator` due to generator comprehensions
   // needs to be before `_shadowFunctions`
   "es7.comprehensions":                    require("./es7/comprehensions"),
@@ -94,8 +94,6 @@ export default {
 
   "spec.protoToAssign":                    require("./spec/proto-to-assign"),
 
-  _declarations:                           require("./internal/declarations"),
-
   _shadowFunctions:                        require("./internal/shadow-functions"),
 
   "es7.doExpressions":                     require("./es7/do-expressions"),
@@ -117,6 +115,6 @@ export default {
   "utility.inlineExpressions":             require("./utility/inline-expressions"),
   "utility.deadCodeElimination":           require("./utility/dead-code-elimination"),
 
-  flow:                                    require("./other/flow"),
-  _cleanUp:                                require("./internal/cleanup")
+  jscript:                                 require("./other/jscript"),
+  flow:                                    require("./other/flow")
 };

src/babel/transformation/transformers/internal/cleanup.js

@@ -1,30 +0,0 @@
-export var SequenceExpression = {
-  exit(node) {
-    if (node.expressions.length === 1) {
-      return node.expressions[0];
-    } else if (!node.expressions.length) {
-      this.remove();
-    }
-  }
-};
-
-export var ExpressionStatement = {
-  exit(node) {
-    if (!node.expression) this.remove();
-  }
-};
-
-export var Binary = {
-  exit(node) {
-    var right = node.right;
-    var left  = node.left;
-
-    if (!left && !right) {
-      this.remove();
-    } else if (!left) {
-      return right;
-    } else if (!right) {
-      return left;
-    }
-  }
-};

src/babel/transformation/transformers/internal/declarations.js

@@ -1,37 +0,0 @@
-import * as strict from "../../helpers/strict";
-import * as t from "../../../types";
-
-export var metadata = {
-  secondPass: true
-};
-
-export function BlockStatement(node, parent, scope, file) {
-  if (!node._declarations) return;
-
-  strict.wrap(node, function () {
-    var kinds = {};
-    var kind;
-
-    for (var i in node._declarations) {
-      var declar = node._declarations[i];
-
-      kind = declar.kind || "var";
-      var declarNode = t.variableDeclarator(declar.id, declar.init);
-
-      if (declar.init) {
-        node.body.unshift(file.attachAuxiliaryComment(t.variableDeclaration(kind, [declarNode])));
-      } else {
-        kinds[kind] ||= [];
-        kinds[kind].push(declarNode);
-      }
-    }
-
-    for (kind in kinds) {
-      node.body.unshift(file.attachAuxiliaryComment(t.variableDeclaration(kind, kinds[kind])));
-    }
-
-    node._declarations = null;
-  });
-}
-
-export { BlockStatement as Program };

src/babel/transformation/transformers/internal/module-formatter.js

@@ -1,6 +1,8 @@
 import * as strict from "../../helpers/strict";
 
 export function Program(program, parent, scope, file) {
+  this.stop();
+
   strict.wrap(program, function () {
     program.body = file.dynamicImports.concat(program.body);
   });

src/babel/transformation/transformers/internal/modules.js

@@ -6,7 +6,7 @@
 
 import * as t from "../../../types";
 
-export function check(node) {
+export function shouldVisit(node) {
   return t.isImportDeclaration(node) || t.isExportDeclaration(node);
 }
 

src/babel/transformation/transformers/internal/shadow-functions.js

@@ -52,11 +52,11 @@ function aliasFunction(getBody, path, scope) {
 
   var state = {
     getArgumentsId() {
-      return argumentsId ||= scope.generateUidIdentifier("arguments");
+      return argumentsId = argumentsId || scope.generateUidIdentifier("arguments");
     },
 
     getThisId() {
-      return thisId ||= scope.generateUidIdentifier("this");
+      return thisId = thisId || scope.generateUidIdentifier("this");
     }
   };
 
@@ -67,7 +67,7 @@ function aliasFunction(getBody, path, scope) {
   var body;
 
   var pushDeclaration = function (id, init) {
-    body ||= getBody();
+    body = body || getBody();
     body.unshift(t.variableDeclaration("var", [
       t.variableDeclarator(id, init)
     ]));
@@ -82,6 +82,10 @@ function aliasFunction(getBody, path, scope) {
   }
 };
 
+export function shouldVisit(node) {
+  return true;
+}
+
 export function Program(node, parent, scope) {
   aliasFunction(function () {
     return node.body;

src/babel/transformation/transformers/internal/strict.js

@@ -13,6 +13,6 @@ export function Program(program, parent, scope, file) {
       }
     }
 
-    program.body.unshift(directive);
+    this.unshiftContainer("body", [directive]);
   }
 }

src/babel/transformation/transformers/internal/validation.js

@@ -21,7 +21,7 @@ export function MethodDefinition(node) {
     var isConstructor = !node.computed && t.isIdentifier(node.key, { name: "constructor" });
 
     // get ["constructor"]() {}
-    isConstructor ||= t.isLiteral(node.key, { value: "constructor" });
+    isConstructor = isConstructor || t.isLiteral(node.key, { value: "constructor" });
 
     if (isConstructor) {
       throw this.errorWithNode(messages.get("classesIllegalConstructorKind"));

src/babel/transformation/transformers/optimisation/flow.for-of.js

@@ -1,7 +1,7 @@
 import { _ForOfStatementArray } from "../es6/for-of";
 import * as t from "../../../types";
 
-export var check = t.isForOfStatement;
+export var shouldVisit = t.isForOfStatement;
 export var optional = true;
 
 export function ForOfStatement(node, parent, scope, file) {

src/babel/transformation/transformers/other/flow.js

@@ -1,5 +1,9 @@
 import * as t from "../../../types";
 
+export function shouldVisit(node) {
+  return node.isType || node.optional || node.implements || node.typeAnnotation || t.isFlow(node);
+}
+
 export function Flow(node) {
   this.remove();
 }

src/babel/transformation/transformers/other/jscript.js

@@ -0,0 +1,18 @@
+import * as t from "../../../types";
+
+export var metadata = {
+  optional: true
+};
+
+export function FunctionExpression(node, print) {
+  if (!node.id) return;
+  node._ignoreUserWhitespace = true;
+
+  return t.callExpression(
+    t.functionExpression(null, [], t.blockStatement([
+      t.toStatement(node),
+      t.returnStatement(node.id)
+    ])),
+    []
+  );
+}

src/babel/transformation/transformers/other/regenerator.js

@@ -1,7 +1,7 @@
 import regenerator from "regenerator";
 import * as t from "../../../types";
 
-export function check(node) {
+export function shouldVisit(node) {
   return t.isFunction(node) && (node.async || node.generator);
 }
 
@@ -9,5 +9,6 @@ export var Program = {
   enter(ast) {
     regenerator.transform(ast);
     this.stop();
+    return ast; // force a checkPath, this really needs to be optimised
   }
 };

src/babel/transformation/transformers/spec/block-scoped-functions.js

@@ -1,8 +1,12 @@
 import * as t from "../../../types";
 
-function statementList(key, node, file) {
-  for (var i = 0; i < node[key].length; i++) {
-    var func = node[key][i];
+function statementList(key, path, file) {
+  var paths = path.get(key);
+
+  for (var i = 0; i < paths.length; i++) {
+    var path = paths[i];
+
+    var func = path.node;
     if (!t.isFunctionDeclaration(func)) continue;
 
     var declar = t.variableDeclaration("let", [
@@ -15,20 +19,33 @@ function statementList(key, node, file) {
     // todo: name this
     func.id = null;
 
-    node[key][i] = declar;
-
-    file.checkNode(declar);
+    path.replaceWith(declar);
   }
 }
 
+export function shouldVisit(node) {
+  var body;
+  if (node.type === "SwitchCase") {
+    body = node.consequent;
+  } else if (node.type === "BlockStatement") {
+    body = node.body;
+  }
+  if (body) {
+    for (var i = 0; i < body.length; i++) {
+      if (body[i].type === "FunctionDeclaration") return true;
+    }
+  }
+  return false;
+}
+
 export function BlockStatement(node, parent, scope, file) {
   if ((t.isFunction(parent) && parent.body === node) || t.isExportDeclaration(parent)) {
     return;
   }
 
-  statementList("body", node, file);
+  statementList("body", this, file);
 }
 
 export function SwitchCase(node, parent, scope, file) {
-  statementList("consequent", node, file);
+  statementList("consequent", this, file);
 }

src/babel/transformation/transformers/spec/function-name.js

@@ -1,2 +1 @@
-export { bare as FunctionExpression } from "../../helpers/name-method";
-export { bare as ArrowFunctionExpression } from "../../helpers/name-method";
+export { bare as FunctionExpression, bare as ArrowFunctionExpression } from "../../helpers/name-method";

src/babel/transformation/transformers/utility/dead-code-elimination.js

@@ -21,6 +21,38 @@ export var metadata = {
   optional: true
 };
 
+export function Identifier(node, parent, scope) {
+  if (!this.isReferenced()) return;
+
+  var binding = scope.getBinding(node.name);
+  if (!binding || binding.references > 1 || !binding.constant) return;
+
+  var replacement = binding.path.node;
+  if (t.isVariableDeclarator(replacement)) {
+    replacement = replacement.init;
+  }
+  t.toExpression(replacement);
+
+  scope.removeBinding(node.name);
+
+  binding.path.remove();
+  return replacement;
+}
+
+export function FunctionDeclaration(node, parent, scope) {
+  var bindingInfo = scope.getBinding(node.id.name);
+  if (bindingInfo && !bindingInfo.referenced) {
+    this.remove();
+  }
+}
+
+export { FunctionDeclaration as ClassDeclaration };
+
+export function VariableDeclarator(node, parent, scope) {
+  if (!t.isIdentifier(node.id) || !scope.isPure(node.init)) return;
+  FunctionDeclaration.apply(this, arguments);
+}
+
 export function ConditionalExpression(node, parent, scope) {
   var evaluateTest = this.get("test").evaluateTruthy();
   if (evaluateTest === true) {

src/babel/transformation/transformers/validation/react.js

@@ -1,6 +1,14 @@
 import * as messages from "../../../messages";
 import * as t from "../../../types";
 
+export var metadata = {
+  readOnly: true
+};
+
+export function shouldVisit(node) {
+  return t.isModuleDeclaration(node) || (t.isCallExpression(node) && t.isIdentifier(node.callee, { name: "require" }));
+}
+
 // check if the input Literal `source` is an alternate casing of "react"
 function check(source, file) {
   if (t.isLiteral(source)) {

src/babel/transformation/transformers/validation/undeclared-variable-check.js

@@ -2,7 +2,8 @@ import levenshtein from "leven";
 import * as messages from "../../../messages";
 
 export var metadata = {
-  optional: true
+  optional: true,
+  readOnly: true
 };
 
 export function Identifier(node, parent, scope, file) {

src/babel/traversal/binding.js

@@ -3,6 +3,8 @@ import * as t from "../types";
 export default class Binding {
   constructor({ identifier, scope, path, kind }) {
     this.identifier = identifier;
+    this.references = 0;
+    this.referenced = false;
     this.constant   = true;
     this.scope      = scope;
     this.path       = path;
@@ -58,6 +60,15 @@ export default class Binding {
     }
   }
 
+  /**
+   * Description
+   */
+
+  reference() {
+    this.referenced = true;
+    this.references++;
+  }
+
   /**
    * Description
    */

src/babel/traversal/context.js

@@ -32,9 +32,10 @@ export default class TraversalContext {
     for (let i = 0; i < queue.length; i++) {
       var path = queue[i];
       if (visited.indexOf(path.node) >= 0) continue;
-
       visited.push(path.node);
 
+      path.setContext(this.parentPath, this, path.key);
+
       if (path.visit()) {
         stop = true;
         break;

src/babel/traversal/explode.js

@@ -0,0 +1,19 @@
+import * as t from "../types";
+
+export default function (obj) {
+  for (var type in obj) {
+    var fns = obj[type];
+    if (typeof fns === "function") {
+      obj[type] = fns = { enter: fns };
+    }
+
+    var aliases = t.FLIPPED_ALIAS_KEYS[type];
+    if (aliases) {
+      for (var i = 0; i < aliases.length; i++) {
+        var alias = aliases[i];
+        obj[alias] = obj[alias] || fns;
+      }
+    }
+  }
+  return obj;
+}

src/babel/traversal/index.js

@@ -1,4 +1,6 @@
 import TraversalContext from "./context";
+import explode from "./explode";
+import * as messages from "../messages";
 import includes from "lodash/collection/includes";
 import * as t from "../types";
 
@@ -7,13 +9,12 @@ export default function traverse(parent, opts, scope, state, parentPath) {
 
   if (!opts.noScope && !scope) {
     if (parent.type !== "Program" && parent.type !== "File") {
-      throw new Error(`Must pass a scope and parentPath unless traversing a Program/File got a ${parent.type} node`);
+      throw new Error(messages.get("traverseNeedsParent", parent.type));
     }
   }
 
   if (!opts) opts = {};
-  if (!opts.enter) opts.enter = function () { };
-  if (!opts.exit) opts.exit = function () { };
+  traverse.verify(opts);
 
   // array of nodes
   if (Array.isArray(parent)) {
@@ -25,6 +26,43 @@ export default function traverse(parent, opts, scope, state, parentPath) {
   }
 }
 
+/**
+ * Quickly iterate over some traversal options and validate them.
+ */
+
+traverse.verify = function (opts) {
+  if (opts._verified) return;
+
+  if (typeof opts === "function") {
+    throw new Error(messages.get("traverseVerifyRootFunction"));
+  }
+
+  if (!opts.enter) opts.enter = function () { };
+  if (!opts.exit) opts.exit = function () { };
+  if (!opts.shouldSkip) opts.shouldSkip = function () { return false; };
+
+  for (var key in opts) {
+    // it's all good
+    if (key === "blacklist") continue;
+
+    var opt = opts[key];
+
+    if (typeof opt === "function") {
+      // it's all good, it's fine for this key to be a function
+      if (key === "enter" || key === "exit" || key === "shouldSkip") continue;
+
+      throw new Error(messages.get("traverseVerifyVisitorFunction", key));
+    } else if (typeof opt === "object") {
+      for (var key2 in opt) {
+        if (key2 === "enter" || key2 === "exit") continue;
+        throw new Error(messages.get("traverseVerifyVisitorProperty", key, key2));
+      }
+    }
+  }
+
+  opts._verified = true;
+};
+
 traverse.node = function (node, opts, scope, state, parentPath) {
   var keys = t.VISITOR_KEYS[node.type];
   if (!keys) return;
@@ -39,7 +77,7 @@ traverse.node = function (node, opts, scope, state, parentPath) {
 
 const CLEAR_KEYS = [
   "trailingComments", "leadingComments", "extendedRange",
-  "_declarations", "_scopeInfo" ,"_paths",
+  "_scopeInfo" ,"_paths",
   "tokens", "range", "start", "end", "loc", "raw"
 ];
 
@@ -75,22 +113,7 @@ traverse.removeProperties = function (tree) {
   return tree;
 };
 
-traverse.explode = function (obj) {
-  for (var type in obj) {
-    var fns = obj[type];
-    if (typeof fns === "function") {
-      obj[type] = fns = { enter: fns };
-    }
-
-    var aliases = t.FLIPPED_ALIAS_KEYS[type];
-    if (aliases) {
-      for (var i = 0; i < aliases.length; i++) {
-        obj[aliases[i]] ||= fns;
-      }
-    }
-  }
-  return obj;
-};
+traverse.explode = explode;
 
 function hasBlacklistedType(node, parent, scope, state) {
   if (node.type === state.type) {