start movement of core into plugins

package.json

@@ -30,6 +30,7 @@
   "dependencies": {
     "acorn-jsx": "^1.0.0",
     "ast-types": "~0.7.0",
+    "babel-plugin-undefined-to-void": "^1.1.0",
     "bluebird": "^2.9.25",
     "chalk": "^1.0.0",
     "convert-source-map": "^1.1.0",

packages/babel-cli/bin/babel-plugin

@@ -0,0 +1,117 @@
+#!/usr/bin/env node
+
+var readline = require("readline");
+var child    = require("child_process");
+var path     = require("path");
+var fs       = require("fs");
+
+function spawn(cmd, args, callback) {
+  console.log(">", cmd, args);
+
+  var spawn = child.spawn(cmd, args, { stdio: "inherit" });
+
+  spawn.on("exit", function (code) {
+    if (code === 0) {
+      if (callback) callback();
+    } else {
+      console.log("Killing...");
+      process.exit(1);
+    }
+  });
+}
+
+function spawnMultiple(cmds) {
+  function next() {
+    var cmd = cmds.shift();
+    if (cmd) {
+      spawn(cmd.command, cmd.args, next);
+    } else {
+      process.exit();
+    }
+  }
+
+  next();
+}
+
+function write(filename, content) {
+  console.log(filename);
+  fs.writeFileSync(filename, content);
+}
+
+var BABEL_PLUGIN_PREFIX = "babel-plugin-";
+
+var cmds = {
+  init: function () {
+    var name = path.basename(process.cwd());
+
+    if (name.indexOf(BABEL_PLUGIN_PREFIX) === 0) {
+      name = name.slice(BABEL_PLUGIN_PREFIX.length);
+    }
+
+    write("package.json", JSON.stringify({
+      name: BABEL_PLUGIN_PREFIX + name,
+      version: "1.0.0",
+      description: "",
+      license: "MIT",
+      main: "lib/index.js",
+
+      devDependencies: {
+        babel: "^5.6.0"
+      },
+
+      peerDependencies: {
+        babel: "^5.6.0"
+      },
+
+      scripts: {
+        build: "babel-plugin build",
+        push:  "babel-plugin publish",
+        test:  "babel-plugin test"
+      },
+
+      keywords: ["babel-plugin"]
+    }, null, "  "));
+
+    write(".npmignore", "node_modules\n*.log\nsrc");
+
+    write(".gitignore", "node_modules\n*.log\nlib");
+
+    fs.mkdirSync("src");
+    write("src/index.js", "");
+  },
+
+  build: function () {
+    spawn("babel", ["src", "--out-dir", "lib"]);
+  },
+
+  publish: function () {
+    var rl = readline.createInterface({
+      input: process.stdin,
+      output: process.stdout
+    });
+
+    var pkg = require(process.cwd() + "/package.json");
+    console.log("Current verison:", pkg.version);
+
+    rl.question("New version (enter nothing for patch): ", function (newVersion) {
+      newVersion = newVersion || "patch";
+
+      spawnMultiple([
+        { command: "git", args: ["pull"] },
+        { command: "git", args: ["push"] },
+        { command: "babel-plugin", args: ["build"] },
+        { command: "npm", args: ["version", newVersion] },
+        { command: "npm", args: ["publish"] },
+        { command: "git", args: ["push", "--follow-tags"] }
+      ]);
+    });
+  }
+};
+
+var cmd = cmds[process.argv[2]];
+if (cmd) {
+  cmd();
+} else {
+  console.error("Unknown command:", cmd);
+  process.exit(1);
+}

packages/babel-cli/package.json

@@ -23,6 +23,7 @@
   "bin": {
     "babel": "./bin/babel/index.js",
     "babel-node": "./bin/babel-node",
-    "babel-external-helpers": "./bin/babel-external-helpers"
+    "babel-external-helpers": "./bin/babel-external-helpers",
+    "babel-plugin": "./bin/babel-plugin"
   }
 }

src/babel/api/node.js

@@ -9,8 +9,9 @@ export { pipeline } from "../transformation";
 export { canCompile } from "../util";
 
 export { default as options } from "../transformation/file/options/config";
+export { default as Plugin } from "../transformation/plugin";
 export { default as Transformer } from "../transformation/transformer";
-export { default as TransformerPipeline } from "../transformation/transformer-pipeline";
+export { default as Pipeline } from "../transformation/pipeline";
 export { default as traverse } from "../traversal";
 export { default as buildExternalHelpers } from "../tools/build-external-helpers";
 export { version } from "../../../package";

src/babel/api/register/node.js

@@ -105,7 +105,7 @@ if (process.env.running_under_istanbul) {
     if (istanbulMonkey[filename]) {
       delete istanbulMonkey[filename];
       var code = compile(filename, {
-        auxiliaryComment: "istanbul ignore next"
+        auxiliaryCommentBefore: "istanbul ignore next"
       });
       istanbulMonkey[filename] = true;
       return code;

src/babel/messages.js

@@ -34,10 +34,10 @@ export const MESSAGES = {
   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",
+  pluginNotTransformer: "The plugin $1 didn't export a Plugin instance",
   pluginUnknown: "Unknown plugin $1",
 
-  transformerNotFile: "Transformer $1 is resolving to a different Babel version to what is doing the actual transformation..."
+  pluginNotFile: "Plugin $1 is resolving to a different Babel version to what is doing the actual transformation..."
 };
 
 export function get(key: String, ...args) {

src/babel/transformation/file/index.js

@@ -4,7 +4,6 @@ import moduleFormatters from "../modules";
 import PluginManager from "./plugin-manager";
 import shebangRegex from "shebang-regex";
 import NodePath from "../../traversal/path";
-import Transformer from "../transformer";
 import isFunction from "lodash/lang/isFunction";
 import isAbsolute from "path-is-absolute";
 import resolveRc from "./options/resolve-rc";
@@ -14,13 +13,14 @@ import codeFrame from "../../helpers/code-frame";
 import defaults from "lodash/object/defaults";
 import includes from "lodash/collection/includes";
 import traverse from "../../traversal";
-import Hub from "../../traversal/hub";
 import assign from "lodash/object/assign";
 import Logger from "./logger";
+import Plugin from "../plugin";
 import parse from "../../helpers/parse";
 import merge from "../../helpers/merge";
 import slash from "slash";
 import clone from "lodash/lang/clone";
+import Hub from "../../traversal/hub";
 import * as util from  "../../util";
 import path from "path";
 import * as t from "../../types";
@@ -246,7 +246,7 @@ export default class File {
 
     // build dependency graph
     for (let pass of (stack: Array)) {
-      for (var dep of (pass.transformer.dependencies: Array)) {
+      for (var dep of (pass.plugin.dependencies: Array)) {
         this.transformerDependencies[dep] = pass.key;
       }
     }
@@ -263,7 +263,7 @@ export default class File {
       // been merged
       if (ignore.indexOf(pass) >= 0) continue;
 
-      var group = pass.transformer.metadata.group;
+      var group = pass.plugin.metadata.group;
 
       // can't merge
       if (!pass.canTransform() || !group) {
@@ -273,7 +273,7 @@ export default class File {
 
       var mergeStack = [];
       for (let pass of (_stack: Array)) {
-        if (pass.transformer.metadata.group === group) {
+        if (pass.plugin.metadata.group === group) {
           mergeStack.push(pass);
           ignore.push(pass);
         }
@@ -281,11 +281,11 @@ export default class File {
 
       var visitors = [];
       for (let pass of (mergeStack: Array)) {
-        visitors.push(pass.handlers);
+        visitors.push(pass.plugin.visitor);
       }
       var visitor = traverse.visitors.merge(visitors);
-      var mergeTransformer = new Transformer(group, visitor);
-      stack.push(mergeTransformer.buildPass(this));
+      var mergePlugin = new Plugin(group, { visitor });
+      stack.push(mergePlugin.buildPass(this));
     }
 
     return stack;
@@ -586,7 +586,7 @@ export default class File {
 
   call(key: string) {
     for (var pass of (this.uncollapsedTransformerStack: Array)) {
-      var fn = pass.transformer[key];
+      var fn = pass.plugin[key];
       if (fn) fn(this);
     }
   }

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

@@ -1,4 +1,13 @@
-import * as node from  "../../api/node";
+import Transformer from "../transformer";
+import Plugin from "../plugin";
+import * as types from "../../types";
+
+var context = {
+  Transformer,
+  Plugin,
+  types
+};
+
 import * as messages from "../../messages";
 import * as util from  "../../util";
 
@@ -11,7 +20,7 @@ export default class PluginManager {
       if (plugin.container === fn) return plugin.transformer;
     }
 
-    var transformer = fn(node);
+    var transformer = fn(context);
     PluginManager.memoisedPlugins.push({
       container: fn,
       transformer: transformer
@@ -55,7 +64,7 @@ export default class PluginManager {
     }
 
     // validate Transformer instance
-    if (!plugin.buildPass || plugin.constructor.name !== "Transformer") {
+    if (!plugin.buildPass || plugin.constructor.name !== "Plugin") {
       throw new TypeError(messages.get("pluginNotTransformer", name));
     }
 

src/babel/transformation/helpers/build-react-transformer.js

@@ -9,8 +9,10 @@ import esutils from "esutils";
 import * as react from "./react";
 import * as t from "../../types";
 
-export default function (exports, opts) {
-  exports.JSXIdentifier = function (node) {
+export default function (opts) {
+  var visitor = {};
+
+  visitor.JSXIdentifier = function (node) {
     if (node.name === "this" && this.isReferenced()) {
       return t.thisExpression();
     } else if (esutils.keyword.isIdentifierNameES6(node.name)) {
@@ -20,22 +22,22 @@ export default function (exports, opts) {
     }
   };
 
-  exports.JSXNamespacedName = function () {
+  visitor.JSXNamespacedName = function () {
     throw this.errorWithNode(messages.get("JSXNamespacedTags"));
   };
 
-  exports.JSXMemberExpression = {
+  visitor.JSXMemberExpression = {
     exit(node) {
       node.computed = t.isLiteral(node.property);
       node.type = "MemberExpression";
     }
   };
 
-  exports.JSXExpressionContainer = function (node) {
+  visitor.JSXExpressionContainer = function (node) {
     return node.expression;
   };
 
-  exports.JSXAttribute = {
+  visitor.JSXAttribute = {
     enter(node) {
       var value = node.value;
       if (t.isLiteral(value) && isString(value.value)) {
@@ -49,7 +51,7 @@ export default function (exports, opts) {
     }
   };
 
-  exports.JSXOpeningElement = {
+  visitor.JSXOpeningElement = {
     exit(node, parent, scope, file) {
       parent.children = react.buildChildren(parent);
 
@@ -139,7 +141,7 @@ export default function (exports, opts) {
     return attribs;
   };
 
-  exports.JSXElement = {
+  visitor.JSXElement = {
     exit(node) {
       var callExpr = node.openingElement;
 
@@ -173,15 +175,15 @@ export default function (exports, opts) {
     }
   };
 
-  exports.ExportDefaultDeclaration = function (node, parent, scope, file) {
+  visitor.ExportDefaultDeclaration = function (node, parent, scope, file) {
     if (react.isCreateClass(node.declaration)) {
       addDisplayName(file.opts.basename, node.declaration);
     }
   };
 
-  exports.AssignmentExpression =
-  exports.Property =
-  exports.VariableDeclarator = function (node) {
+  visitor.AssignmentExpression =
+  visitor.Property =
+  visitor.VariableDeclarator = function (node) {
     var left, right;
 
     if (t.isAssignmentExpression(node)) {
@@ -203,4 +205,6 @@ export default function (exports, opts) {
       addDisplayName(left.name, right);
     }
   };
+
+  return visitor;
 }

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

@@ -68,10 +68,10 @@ var visit = function (node, name, scope) {
   // check to see if we have a local binding of the id we're setting inside of
   // the function, this is important as there are caveats associated
 
-  var bindingInfo = scope.getOwnBinding(name);
+  var binding = scope.getOwnBinding(name);
 
-  if (bindingInfo) {
-    if (bindingInfo.kind === "param") {
+  if (binding) {
+    if (binding.kind === "param") {
       // safari will blow up in strict mode with code like:
       //
       //   var t = function t(t) {};
@@ -133,8 +133,8 @@ export function bare(node, parent, scope) {
     id = parent.id;
 
     if (t.isIdentifier(id)) {
-      var bindingInfo = scope.parent.getBinding(id.name);
-      if (bindingInfo && bindingInfo.constant && scope.getBinding(id.name) === bindingInfo) {
+      var binding = scope.parent.getBinding(id.name);
+      if (binding && binding.constant && scope.getBinding(id.name) === binding) {
         // always going to reference this method
         node.id = id;
         return;

src/babel/transformation/index.js

@@ -1,4 +1,4 @@
-import Pipeline from "./transformer-pipeline";
+import Pipeline from "./pipeline";
 
 var pipeline = new Pipeline;
 
@@ -8,8 +8,11 @@ import transformers from "./transformers";
 
 for (var key in transformers) {
   var transformer = transformers[key];
+
+  if (typeof transformer === "object") {
     var metadata = transformer.metadata = transformer.metadata || {};
     metadata.group = metadata.group || "builtin-basic";
+  }
 }
 
 pipeline.addTransformers(transformers);

src/babel/transformation/pipeline.js

@@ -1,10 +1,11 @@
-import Transformer from "./transformer";
+import PluginManager from "./file/plugin-manager";
 import normalizeAst from "../helpers/normalize-ast";
+import Plugin from "./plugin";
 import assign from "lodash/object/assign";
 import object from "../helpers/object";
 import File from "./file";
 
-export default class TransformerPipeline {
+export default class Pipeline {
   constructor() {
     this.transformers = object();
     this.namespaces   = object();
@@ -20,7 +21,7 @@ export default class TransformerPipeline {
     return this;
   }
 
-  addTransformer(key, transformer) {
+  addTransformer(key, plugin) {
     if (this.transformers[key]) throw new Error(); // todo: error
 
     var namespace = key.split(".")[0];
@@ -28,7 +29,15 @@ export default class TransformerPipeline {
     this.namespaces[namespace].push(key);
     this.namespaces[key] = namespace;
 
-    this.transformers[key] = new Transformer(key, transformer);
+    if (typeof plugin === "function") {
+      plugin = PluginManager.memoisePluginContainer(plugin);
+      plugin.key = key;
+      plugin.metadata.optional = true;
+    } else {
+      plugin = new Plugin(key, plugin);
+    }
+
+    this.transformers[key] = plugin;
   }
 
   addAliases(names) {
@@ -46,17 +55,24 @@ export default class TransformerPipeline {
     return this;
   }
 
-  canTransform(transformer, fileOpts) {
-    if (transformer.metadata.plugin) return true;
+  canTransform(plugin, fileOpts) {
+    if (plugin.metadata.plugin) {
+      return true;
+    }
 
     for (var filter of (this.filters: Array)) {
-      var result = filter(transformer, fileOpts);
+      var result = filter(plugin, fileOpts);
       if (result != null) return result;
     }
 
     return true;
   }
 
+  analyze(code: string, opts?: Object = {}) {
+    opts.code = false;
+    return this.transform(code, opts);
+  }
+
   pretransform(code: string, opts?: Object) {
     var file = new File(opts, this);
     return file.wrap(code, function () {

src/babel/transformation/plugin-pass.js

@@ -7,14 +7,13 @@ import type File from "./file";
  * AST and running it's parent transformers handlers over it.
  */
 
-export default class TransformerPass {
-  constructor(file: File, transformer: Transformer) {
-    this.transformer = transformer;
-    this.handlers    = transformer.handlers;
+export default class PluginPass {
+  constructor(file: File, plugin: Transformer) {
+    this.plugin = plugin;
     this.file   = file;
-    this.key         = transformer.key;
+    this.key    = plugin.key;
 
-    if (this.canTransform() && transformer.metadata.experimental && !file.opts.experimental) {
+    if (this.canTransform() && plugin.metadata.experimental && !file.opts.experimental) {
       file.log.warn(`THE TRANSFORMER ${this.key} HAS BEEN MARKED AS EXPERIMENTAL AND IS WIP. USE AT YOUR OWN RISK. ` +
                     "THIS WILL HIGHLY LIKELY BREAK YOUR CODE SO USE WITH **EXTREME** CAUTION. ENABLE THE " +
                     "`experimental` OPTION TO IGNORE THIS WARNING.");
@@ -23,13 +22,13 @@ export default class TransformerPass {
 
   canTransform(): boolean {
     return this.file.transformerDependencies[this.key] ||
-           this.file.pipeline.canTransform(this.transformer, this.file.opts);
+           this.file.pipeline.canTransform(this.plugin, this.file.opts);
   }
 
   transform() {
     var file = this.file;
     file.log.debug(`Start transformer ${this.key}`);
-    traverse(file.ast, this.handlers, file.scope, file);
+    traverse(file.ast, this.plugin.visitor, file.scope, file);
     file.log.debug(`Finish transformer ${this.key}`);
   }
 }

src/babel/transformation/plugin.js

@@ -0,0 +1,55 @@
+import PluginPass from "./plugin-pass";
+import * as messages from "../messages";
+import isFunction from "lodash/lang/isFunction";
+import traverse from "../traversal";
+import assign from "lodash/object/assign";
+import clone from "lodash/lang/clone";
+import File from "./file";
+
+export default class Plugin {
+  constructor(key: string, plugin: Object) {
+    plugin = assign({}, plugin);
+
+    var take = function (key) {
+      var val = plugin[key];
+      delete plugin[key];
+      return val;
+    };
+
+    this.manipulateOptions = take("manipulateOptions");
+    this.metadata          = take("metadata") || {};
+    this.dependencies      = this.metadata.dependencies || [];
+    this.post              = take("post");
+    this.pre               = take("pre");
+
+    //
+
+    if (this.metadata.stage != null) {
+      this.metadata.optional = true;
+    }
+
+    //
+
+    this.visitor = this.normalize(clone(take("visitor")) || {});
+    this.key     = key;
+  }
+
+  normalize(visitor: Object): Object {
+    if (isFunction(visitor)) {
+      visitor = { ast: visitor };
+    }
+
+    traverse.explode(visitor);
+
+    return visitor;
+  }
+
+  buildPass(file: File): PluginPass {
+    // validate Transformer instance
+    if (!(file instanceof File)) {
+      throw new TypeError(messages.get("pluginNotFile", this.key));
+    }
+
+    return new PluginPass(file, this);
+  }
+}

src/babel/transformation/transformer.js

@@ -1,82 +1,14 @@
-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";
-import assign from "lodash/object/assign";
-import File from "./file";
-import each from "lodash/collection/each";
-
-/**
- * This is the class responsible for normalising a transformers handlers
- * as well as constructing a `TransformerPass` that is responsible for
- * actually running the transformer over the provided `File`.
- */
+import Plugin from "./plugin";
 
 export default class Transformer {
-  constructor(transformerKey: string, transformer: Object) {
-    transformer = assign({}, transformer);
+  constructor(key, obj) {
+    var plugin = {};
 
-    var take = function (key) {
-      var val = transformer[key];
-      delete transformer[key];
-      return val;
-    };
+    plugin.metadata = obj.metadata;
+    delete obj.metadata;
 
-    this.manipulateOptions = take("manipulateOptions");
-    this.metadata          = take("metadata") || {};
-    this.dependencies      = this.metadata.dependencies || [];
-    this.parser            = take("parser");
-    this.post              = take("post");
-    this.pre               = take("pre");
+    plugin.visitor = obj;
 
-    //
-
-    if (this.metadata.stage != null) {
-      this.metadata.optional = true;
-    }
-
-    //
-
-    this.handlers = this.normalize(transformer);
-    this.key      = transformerKey;
-  }
-
-  normalize(transformer: Object): Object {
-    if (isFunction(transformer)) {
-      transformer = { ast: transformer };
-    }
-
-    traverse.explode(transformer);
-
-    each(transformer, (fns, type) => {
-      // hidden property
-      if (type[0] === "_") {
-        this[type] = fns;
-        return;
-      }
-
-      if (type === "enter" || type === "exit") return;
-
-      if (isFunction(fns)) fns = { enter: fns };
-
-      if (!isObject(fns)) return;
-
-      if (!fns.enter) fns.enter = function () { };
-      if (!fns.exit) fns.exit = function () { };
-
-      transformer[type] = fns;
-    });
-
-    return transformer;
-  }
-
-  buildPass(file: File): TransformerPass {
-    // validate Transformer instance
-    if (!(file instanceof File)) {
-      throw new TypeError(messages.get("transformerNotFile", this.key));
-    }
-
-    return new TransformerPass(file, this);
+    return new Plugin(key, plugin);
   }
 }

src/babel/transformation/transformers/es3/member-expression-literals.js

@@ -4,7 +4,8 @@ export var metadata = {
   group: "builtin-trailing"
 };
 
-export var MemberExpression = {
+export var visitor = {
+  MemberExpression: {
     exit(node) {
       var prop = node.property;
       if (!node.computed && t.isIdentifier(prop) && !t.isValidIdentifier(prop.name)) {
@@ -13,4 +14,5 @@ export var MemberExpression = {
         node.computed = true;
       }
     }
+  }
 };

src/babel/transformation/transformers/es3/property-literals.js

@@ -4,7 +4,8 @@ export var metadata = {
   group: "builtin-trailing"
 };
 
-export var Property = {
+export var visitor = {
+  Property: {
     exit(node) {
       var key = node.key;
       if (!node.computed && t.isIdentifier(key) && !t.isValidIdentifier(key.name)) {
@@ -12,4 +13,5 @@ export var Property = {
         node.key = t.literal(key.name);
       }
     }
+  }
 };

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

@@ -1,7 +1,8 @@
 import * as defineMap from "../../helpers/define-map";
 import * as t from "../../../types";
 
-export function ObjectExpression(node, parent, scope, file) {
+export var visitor = {
+  ObjectExpression(node, parent, scope, file) {
     var hasAny = false;
     for (var prop of (node.properties: Array)) {
       if (prop.kind === "get" || prop.kind === "set") {
@@ -26,4 +27,5 @@ export function ObjectExpression(node, parent, scope, file) {
       t.memberExpression(t.identifier("Object"), t.identifier("defineProperties")),
       [node, defineMap.toDefineObject(mutatorMap)]
     );
-}
+  }
+};

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

@@ -1,9 +1,11 @@
 import * as t from "../../../types";
 
-export function ArrowFunctionExpression(node) {
+export var visitor = {
+  ArrowFunctionExpression(node) {
     t.ensureBlock(node);
 
     node.expression = false;
     node.type = "FunctionExpression";
     node.shadow = true;
-}
+  }
+};

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

@@ -44,7 +44,8 @@ export var metadata = {
   group: "builtin-advanced"
 };
 
-export function VariableDeclaration(node, parent, scope, file) {
+export var visitor = {
+  VariableDeclaration(node, parent, scope, file) {
     if (!isLet(node, parent)) return;
 
     if (isLetInitable(node) && file.transformers["es6.spec.blockScoping"].canTransform()) {
@@ -64,9 +65,9 @@ export function VariableDeclaration(node, parent, scope, file) {
 
       return nodes;
     }
-}
+  },
 
-export function Loop(node, parent, scope, file) {
+  Loop(node, parent, scope, file) {
     var init = node.left || node.init;
     if (isLet(init, node)) {
       t.ensureBlock(node);
@@ -75,16 +76,15 @@ export function Loop(node, parent, scope, file) {
 
     var blockScoping = new BlockScoping(this, this.get("body"), parent, scope, file);
     return blockScoping.run();
-}
+  },
 
-export function BlockStatement(block, parent, scope, file) {
+  "BlockStatement|Program"(block, parent, scope, file) {
     if (!t.isLoop(parent)) {
       var blockScoping = new BlockScoping(null, this, parent, scope, file);
       blockScoping.run();
     }
-}
-
-export { BlockStatement as Program };
+  }
+};
 
 function replace(node, parent, scope, remaps) {
   var remap = remaps[node.name];

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

@@ -10,15 +10,17 @@ import * as t from "../../../types";
 
 const PROPERTY_COLLISION_METHOD_NAME = "__initializeProperties";
 
-export function ClassDeclaration(node, parent, scope, file) {
+export var visitor = {
+  ClassDeclaration(node) {
     return t.variableDeclaration("let", [
       t.variableDeclarator(node.id, t.toExpression(node))
     ]);
-}
+  },
 
-export function ClassExpression(node, parent, scope, file) {
+  ClassExpression(node, parent, scope, file) {
     return new ClassTransformer(this, file).run();
-}
+  }
+};
 
 var collectPropertyReferencesVisitor = {
   Identifier: {

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

@@ -1,6 +1,7 @@
 import * as messages from "../../../messages";
 
-export function Scope(node, parent, scope) {
+export var visitor = {
+  Scope(node, parent, scope) {
     for (var name in scope.bindings) {
       var binding = scope.bindings[name];
 
@@ -11,8 +12,9 @@ export function Scope(node, parent, scope) {
         throw violation.errorWithNode(messages.get("readOnly", name));
       }
     }
-}
+  },
 
-export function VariableDeclaration(node) {
+  VariableDeclaration(node) {
     if (node.kind === "const") node.kind = "let";
-}
+  }
+};

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

@@ -5,7 +5,8 @@ export var metadata = {
   group: "builtin-advanced"
 };
 
-export function ForOfStatement(node, parent, scope, file) {
+export var visitor = {
+  ForXStatement(node, parent, scope, file) {
     var left = node.left;
 
     if (t.isPattern(left)) {
@@ -51,11 +52,9 @@ export function ForOfStatement(node, parent, scope, file) {
 
     var block = node.body;
     block.body = nodes.concat(block.body);
-}
+  },
 
-export { ForOfStatement as ForInStatement };
-
-export function Func/*tion*/(node, parent, scope, file) {
+  Function(node, parent, scope, file) {
     var hasDestructuring = false;
     for (let pattern of (node.params: Array)) {
       if (t.isPattern(pattern)) {
@@ -89,9 +88,9 @@ export function Func/*tion*/(node, parent, scope, file) {
 
     var block = node.body;
     block.body = nodes.concat(block.body);
-}
+  },
 
-export function CatchClause(node, parent, scope, file) {
+  CatchClause(node, parent, scope, file) {
     var pattern = node.param;
     if (!t.isPattern(pattern)) return;
 
@@ -109,9 +108,9 @@ export function CatchClause(node, parent, scope, file) {
     destructuring.init(pattern, ref);
 
     node.body.body = nodes.concat(node.body.body);
-}
+  },
 
-export function AssignmentExpression(node, parent, scope, file) {
+  AssignmentExpression(node, parent, scope, file) {
     if (!t.isPattern(node.left)) return;
 
     var nodes = [];
@@ -143,18 +142,9 @@ export function AssignmentExpression(node, parent, scope, file) {
     }
 
     return nodes;
-}
+  },
 
-function variableDeclarationHasPattern(node) {
-  for (var i = 0; i < node.declarations.length; i++) {
-    if (t.isPattern(node.declarations[i].id)) {
-      return true;
-    }
-  }
-  return false;
-}
-
-export function VariableDeclaration(node, parent, scope, file) {
+  VariableDeclaration(node, parent, scope, file) {
     if (t.isForXStatement(parent)) return;
     if (!variableDeclarationHasPattern(node)) return;
 
@@ -208,6 +198,16 @@ export function VariableDeclaration(node, parent, scope, file) {
     }
 
     return nodes;
+  }
+};
+
+function variableDeclarationHasPattern(node) {
+  for (var i = 0; i < node.declarations.length; i++) {
+    if (t.isPattern(node.declarations[i].id)) {
+      return true;
+    }
+  }
+  return false;
 }
 
 function hasRest(pattern) {

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

@@ -2,7 +2,8 @@ import * as messages from "../../../messages";
 import * as util from  "../../../util";
 import * as t from "../../../types";
 
-export function ForOfStatement(node, parent, scope, file) {
+export var visitor = {
+  ForOfStatement(node, parent, scope, file) {
     if (this.get("right").isArrayExpression()) {
       return _ForOfStatementArray.call(this, node, scope, file);
     }
@@ -35,7 +36,8 @@ export function ForOfStatement(node, parent, scope, file) {
     } else {
       return build.node;
     }
-}
+  }
+};
 
 export function _ForOfStatementArray(node, scope, file) {
   var nodes = [];

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

@@ -12,7 +12,8 @@ export var metadata = {
   group: "builtin-modules"
 };
 
-export function ImportDeclaration(node, parent, scope, file) {
+export var visitor = {
+  ImportDeclaration(node, parent, scope, file) {
     // flow type
     if (node.isType) return;
 
@@ -32,23 +33,23 @@ export function ImportDeclaration(node, parent, scope, file) {
     }
 
     return nodes;
-}
+  },
 
-export function ExportAllDeclaration(node, parent, scope, file) {
+  ExportAllDeclaration(node, parent, scope, file) {
     var nodes = [];
     file.moduleFormatter.exportAllDeclaration(node, nodes, parent);
     keepBlockHoist(node, nodes);
     return nodes;
-}
+  },
 
-export function ExportDefaultDeclaration(node, parent, scope, file) {
+  ExportDefaultDeclaration(node, parent, scope, file) {
     var nodes = [];
     file.moduleFormatter.exportDeclaration(node, nodes, parent);
     keepBlockHoist(node, nodes);
     return nodes;
-}
+  },
 
-export function ExportNamedDeclaration(node, parent, scope, file) {
+  ExportNamedDeclaration(node, parent, scope, file) {
     // flow type
     if (this.get("declaration").isTypeAlias()) return;
 
@@ -72,4 +73,5 @@ export function ExportNamedDeclaration(node, parent, scope, file) {
     keepBlockHoist(node, nodes);
 
     return nodes;
-}
+  }
+};

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

@@ -17,7 +17,8 @@ function Property(path, node, scope, getObjectRef, file) {
   replaceSupers.replace();
 }
 
-export function ObjectExpression(node, parent, scope, file) {
+export var visitor = {
+  ObjectExpression(node, parent, scope, file) {
     var objectRef;
     var getObjectRef = () => objectRef = objectRef || scope.generateUidIdentifier("obj");
 
@@ -30,4 +31,5 @@ export function ObjectExpression(node, parent, scope, file) {
       scope.push({ id: objectRef });
       return t.assignmentExpression("=", objectRef, node);
     }
-}
+  }
+};

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

@@ -22,7 +22,8 @@ var iifeVisitor = {
   }
 };
 
-export function Func/*tion*/(node, parent, scope, file) {
+export var visitor = {
+  Function(node, parent, scope, file) {
     if (!hasDefaults(node)) return;
 
     // ensure it's a block, useful for arrow functions
@@ -115,4 +116,5 @@ export function Func/*tion*/(node, parent, scope, file) {
     } else {
       node.body.body = body.concat(node.body.body);
     }
-}
+  }
+};

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

@@ -58,11 +58,12 @@ function optimizeMemberExpression(parent, offset) {
   }
 }
 
-var hasRest = function (node) {
+function hasRest(node) {
   return t.isRestElement(node.params[node.params.length - 1]);
-};
+}
 
-export function Func/*tion*/(node, parent, scope, file) {
+export var visitor = {
+  Function(node, parent, scope) {
     if (!hasRest(node)) return;
 
     var restParam = node.params.pop();
@@ -145,4 +146,5 @@ export function Func/*tion*/(node, parent, scope, file) {
     });
     loop._blockHoist = node.params.length + 1;
     node.body.body.unshift(loop);
-}
+  }
+};

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

@@ -63,7 +63,8 @@ function spec(node, body, objId, initProps, file) {
   }
 }
 
-export var ObjectExpression = {
+export var visitor = {
+  ObjectExpression: {
     exit(node, parent, scope, file) {
       var hasComputed = false;
 
@@ -99,4 +100,5 @@ export var ObjectExpression = {
 
       return body;
     }
+  }
 };

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

@@ -1,4 +1,5 @@
-export function Property(node) {
+export var visitor = {
+  Property(node) {
     if (node.method) {
       node.method = false;
     }
@@ -6,4 +7,5 @@ export function Property(node) {
     if (node.shorthand) {
       node.shorthand = false;
     }
-}
+  }
+};

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

@@ -1,10 +1,12 @@
 import * as regex from "../../helpers/regex";
 import * as t from "../../../types";
 
-export function Literal(node) {
+export var visitor = {
+  Literal(node) {
     if (!regex.is(node, "y")) return;
     return t.newExpression(t.identifier("RegExp"), [
       t.literal(node.regex.pattern),
       t.literal(node.regex.flags)
     ]);
-}
+  }
+};

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

@@ -1,8 +1,10 @@
 import rewritePattern from "regexpu/rewrite-pattern";
 import * as regex from "../../helpers/regex";
 
-export function Literal(node) {
+export var visitor = {
+  Literal(node) {
     if (!regex.is(node, "u")) return;
     node.regex.pattern = rewritePattern(node.regex.pattern, node.regex.flags);
     regex.pullFlag(node, "u");
-}
+  }
+};

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

@@ -15,7 +15,7 @@ function references(node, scope, state) {
   return scope.getBindingIdentifier(node.name) === declared;
 }
 
-var visitor = {
+var refVisitor = {
   ReferencedIdentifier(node, parent, scope, state) {
     if (t.isFor(parent) && parent.left === node) return;
 
@@ -62,16 +62,16 @@ export var metadata = {
   group: "builtin-advanced"
 };
 
-export var BlockStatement = {
+export var visitor = {
+  "Program|Loop|BlockStatement": {
     exit(node, parent, scope, file) {
       var letRefs = node._letReferences;
       if (!letRefs) return;
 
-    this.traverse(visitor, {
+      this.traverse(refVisitor, {
         letRefs: letRefs,
         file:    file
       });
     }
+  }
 };
-
-export { BlockStatement as Program, BlockStatement as Loop };

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

@@ -4,7 +4,8 @@ export var metadata = {
   optional: true
 };
 
-export function UnaryExpression(node, parent, scope, file) {
+export var visitor = {
+  UnaryExpression(node, parent, scope, file) {
     if (node._ignoreSpecSymbols) return;
 
     if (node.operator === "typeof") {
@@ -22,16 +23,15 @@ export function UnaryExpression(node, parent, scope, file) {
         return call;
       }
     }
-}
+  },
 
-export function BinaryExpression(node, parent, scope, file) {
+  BinaryExpression(node, parent, scope, file) {
     if (node.operator === "instanceof") {
       return t.callExpression(file.addHelper("instanceof"), [node.left, node.right]);
     }
-}
+  },
 
-export function VariableDeclaration(node) {
+  "VariableDeclaration|FunctionDeclaration"(node) {
     if (node._generated) this.skip();
-}
-
-export { VariableDeclaration as FunctionDeclaration };
+  }
+};

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

@@ -5,10 +5,12 @@ export var metadata = {
   group: "builtin-pre"
 };
 
-export function TemplateLiteral(node, parent, scope, file) {
+export var visitor = {
+  TemplateLiteral(node, parent) {
     if (t.isTaggedTemplateExpression(parent)) return;
 
     for (var i = 0; i < node.expressions.length; i++) {
       node.expressions[i] = t.callExpression(t.identifier("String"), [node.expressions[i]]);
     }
-}
+  }
+};

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

@@ -43,7 +43,8 @@ function build(props, scope) {
   return nodes;
 }
 
-export function ArrayExpression(node, parent, scope) {
+export var visitor = {
+  ArrayExpression(node, parent, scope) {
     var elements = node.elements;
     if (!hasSpread(elements)) return;
 
@@ -56,9 +57,9 @@ export function ArrayExpression(node, parent, scope) {
     }
 
     return t.callExpression(t.memberExpression(first, t.identifier("concat")), nodes);
-}
+  },
 
-export function CallExpression(node, parent, scope) {
+  CallExpression(node, parent, scope) {
     var args = node.arguments;
     if (!hasSpread(args)) return;
 
@@ -96,9 +97,9 @@ export function CallExpression(node, parent, scope) {
     }
 
     node.arguments.unshift(contextLiteral);
-}
+  },
 
-export function NewExpression(node, parent, scope, file) {
+  NewExpression(node, parent, scope, file) {
     var args = node.arguments;
     if (!hasSpread(args)) return;
 
@@ -115,4 +116,5 @@ export function NewExpression(node, parent, scope, file) {
       ),
       []
     );
-}
+  }
+};

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

@@ -9,11 +9,13 @@ export var metadata = {
   group: "builtin-trailing"
 };
 
-export function Func/*tion*/(node, parent, scope, file) {
+export var visitor = {
+  Function(node, parent, scope, file) {
     if (node.generator || node.async) return;
     var tailCall = new TailCallTransformer(this, scope, file);
     tailCall.run();
-}
+  }
+};
 
 function returnBlock(expr) {
   return t.blockStatement([t.returnStatement(expr)]);

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

@@ -6,6 +6,10 @@ export var metadata = {
   group: "builtin-pre"
 };
 
+function isString(node) {
+  return t.isLiteral(node) && typeof node.value === "string";
+}
+
 function buildBinaryExpression(left, right) {
   var node = t.binaryExpression("+", left, right);
   node._templateLiteralProduced = true;
@@ -21,7 +25,8 @@ function crawl(path) {
   }
 }
 
-export function TaggedTemplateExpression(node, parent, scope, file) {
+export var visitor = {
+  TaggedTemplateExpression(node, parent, scope, file) {
     var quasi = node.quasi;
     var args  = [];
 
@@ -43,13 +48,9 @@ export function TaggedTemplateExpression(node, parent, scope, file) {
     args = args.concat(quasi.expressions);
 
     return t.callExpression(node.tag, args);
-}
+  },
 
-function isString(node) {
-  return t.isLiteral(node) && typeof node.value === "string";
-}
-
-export function TemplateLiteral(node, parent, scope, file) {
+  TemplateLiteral(node, parent, scope, file) {
     var nodes = [];
 
     for (let elem of (node.quasis: Array)) {
@@ -84,4 +85,5 @@ export function TemplateLiteral(node, parent, scope, file) {
     } else {
       return nodes[0];
     }
-}
+  }
+};

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

@@ -7,11 +7,13 @@ export var metadata = {
   stage: 0
 };
 
-export function ComprehensionExpression(node, parent, scope, file) {
+export var visitor = {
+  ComprehensionExpression(node, parent, scope) {
     var callback = array;
     if (node.generator) callback = generator;
     return callback(node, parent, scope);
-}
+  }
+};
 
 function generator(node) {
   var body = [];

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

@@ -8,7 +8,8 @@ export var metadata = {
   stage: 1
 };
 
-export function ObjectExpression(node, parent, scope, file) {
+export var visitor = {
+  ObjectExpression(node, parent, scope, file) {
     var hasDecorators = false;
     for (let i = 0; i < node.properties.length; i++) {
       let prop = node.properties[i];
@@ -39,4 +40,5 @@ export function ObjectExpression(node, parent, scope, file) {
     var obj = defineMap.toClassObject(mutatorMap);
     obj = defineMap.toComputedObjectFromClass(obj);
     return t.callExpression(file.addHelper("create-decorated-object"), [obj]);
-}
+  }
+};

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

@@ -5,11 +5,13 @@ export var metadata = {
   stage: 0
 };
 
-export function DoExpression(node) {
+export var visitor = {
+  DoExpression(node) {
     var body = node.body.body;
     if (body.length) {
       return body;
     } else {
       return t.identifier("undefined");
     }
-}
+  }
+};

src/babel/transformation/transformers/es7/exponentiation-operator.js

@@ -9,20 +9,10 @@ export var metadata = {
 
 var MATH_POW = t.memberExpression(t.identifier("Math"), t.identifier("pow"));
 
-var {
-  ExpressionStatement,
-  AssignmentExpression,
-  BinaryExpression
-} = build({
+export var visitor = build({
   operator: "**",
 
   build(left, right) {
     return t.callExpression(MATH_POW, [left, right]);
   }
 });
-
-export {
-  ExpressionStatement,
-  AssignmentExpression,
-  BinaryExpression
-};

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

@@ -26,7 +26,8 @@ function build(node, nodes, scope) {
   build(node, nodes, scope);
 }
 
-export function ExportNamedDeclaration(node, parent, scope) {
+export var visitor = {
+  ExportNamedDeclaration(node, parent, scope) {
     var nodes = [];
     build(node, nodes, scope);
     if (!nodes.length) return;
@@ -36,4 +37,5 @@ export function ExportNamedDeclaration(node, parent, scope) {
     }
 
     return nodes;
-}
+  }
+};

src/babel/transformation/transformers/es7/function-bind.js

@@ -36,16 +36,18 @@ function inferBindContext(bind, scope) {
   return tempId;
 }
 
-export function CallExpression(node, parent, scope, file) {
+export var visitor = {
+  CallExpression(node, parent, scope) {
     var bind = node.callee;
     if (!t.isBindExpression(bind)) return;
 
     var context = inferBindContext(bind, scope);
     node.callee = t.memberExpression(bind.callee, t.identifier("call"));
     node.arguments.unshift(context);
-}
+  },
 
-export function BindExpression(node, parent, scope, file) {
+  BindExpression(node, parent, scope) {
     var context = inferBindContext(node, scope);
     return t.callExpression(t.memberExpression(node.callee, t.identifier("bind")), [context]);
-}
+  }
+};

src/babel/transformation/transformers/es7/object-rest-spread.js

@@ -16,7 +16,8 @@ var hasSpread = function (node) {
   return false;
 };
 
-export function ObjectExpression(node, parent, scope, file) {
+export var visitor = {
+  ObjectExpression(node, parent, scope, file) {
     if (!hasSpread(node)) return;
 
     var args = [];
@@ -45,4 +46,5 @@ export function ObjectExpression(node, parent, scope, file) {
     }
 
     return t.callExpression(file.addHelper("extends"), args);
-}
+  }
+};

src/babel/transformation/transformers/index.js

@@ -53,7 +53,7 @@ export default {
   "es7.doExpressions":                     require("./es7/do-expressions"),
   "es6.spec.symbols":                      require("./es6/spec.symbols"),
   "es7.functionBind":                      require("./es7/function-bind"),
-  "spec.undefinedToVoid":                  require("./spec/undefined-to-void"),
+  "spec.undefinedToVoid":                  require("babel-plugin-undefined-to-void"),
 
   //- builtin-advanced
   "es6.destructuring":                     require("./es6/destructuring"),

src/babel/transformation/transformers/internal/block-hoist.js

@@ -11,7 +11,8 @@ export var metadata = {
 //  - 2 Priority over normal nodes
 //  - 3 We want this to be at the **very** top
 
-export var BlockStatement = {
+export var visitor = {
+  Block: {
     exit(node) {
       var hasChange = false;
       for (var i = 0; i < node.body.length; i++) {
@@ -29,6 +30,5 @@ export var BlockStatement = {
         return -1 * priority;
       });
     }
+  }
 };
-
-export { BlockStatement as Program };

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

@@ -25,9 +25,10 @@ function buildListClone(listKey, bindingKey, refKey) {
   };
 }
 
-export var Property = buildClone("value", "key", function (node) {
+export var visitor = {
+  Property: buildClone("value", "key", function (node) {
     return t.isAssignmentPattern(node.value) && node.value.left === node.key;
-});
-
-export var ExportDeclaration = buildListClone("specifiers", "local", "exported");
-export var ImportDeclaration = buildListClone("specifiers", "local", "imported");
+  }),
+  ExportDeclaration: buildListClone("specifiers", "local", "exported"),
+  ImportDeclaration: buildListClone("specifiers", "local", "imported")
+};

src/babel/transformation/transformers/internal/hoist-directives.js

@@ -4,7 +4,8 @@ export var metadata = {
   group: "builtin-pre"
 };
 
-export var BlockStatement = {
+export var visitor = {
+  Block: {
     exit(node) {
       for (var i = 0; i < node.body.length; i++) {
         var bodyNode = node.body[i];
@@ -15,6 +16,5 @@ export var BlockStatement = {
         }
       }
     }
+  }
 };
-
-export { BlockStatement as Program };

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

@@ -2,7 +2,8 @@ export var metadata = {
   group: "builtin-modules"
 };
 
-export var Program = {
+export var visitor = {
+  Program: {
     exit(program, parent, scope, file) {
       // ensure that these are at the top, just like normal imports
       for (var node of (file.dynamicImports: Array)) {
@@ -17,4 +18,5 @@ export var Program = {
         file.moduleFormatter.transform(program);
       }
     }
+  }
 };

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

@@ -15,11 +15,16 @@ function getDeclar(node) {
   return declar;
 }
 
+function buildExportSpecifier(id) {
+  return t.exportSpecifier(clone(id), clone(id));
+}
+
 export var metadata = {
   group: "builtin-pre"
 };
 
-export function ExportDefaultDeclaration(node, parent, scope) {
+export var visitor = {
+  ExportDefaultDeclaration(node, parent, scope) {
     var declar = node.declaration;
 
     if (t.isClassDeclaration(declar)) {
@@ -45,13 +50,9 @@ export function ExportDefaultDeclaration(node, parent, scope) {
       node.declaration = declar.id;
       return nodes;
     }
-}
+  },
 
-function buildExportSpecifier(id) {
-  return t.exportSpecifier(clone(id), clone(id));
-}
-
-export function ExportNamedDeclaration(node, parent, scope) {
+  ExportNamedDeclaration(node) {
     var declar = node.declaration;
 
     if (t.isClassDeclaration(declar)) {
@@ -78,9 +79,9 @@ export function ExportNamedDeclaration(node, parent, scope) {
       }
       return [declar, t.exportNamedDeclaration(null, specifiers)];
     }
-}
+  },
 
-export var Program = {
+  Program: {
     enter(node) {
       var imports = [];
       var rest    = [];
@@ -104,4 +105,5 @@ export var Program = {
         file.moduleFormatter.setup();
       }
     }
+  }
 };

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

@@ -22,12 +22,14 @@ function remap(path, key, create) {
   return id;
 }
 
-export function ThisExpression() {
+export var visitor = {
+  ThisExpression() {
     return remap(this, "this", () => t.thisExpression());
-}
+  },
 
-export function ReferencedIdentifier(node) {
+  ReferencedIdentifier(node) {
     if (node.name === "arguments" && !node._shadowedFunctionLiteral) {
       return remap(this, "arguments", () => t.identifier("arguments"));
     }
-}
+  }
+};

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

@@ -5,17 +5,16 @@ export var metadata = {
   group: "builtin-pre"
 };
 
-export function ForOfStatement(node, parent, scope, file) {
+export var visitor = {
+  ForXStatement(node, parent, scope, file) {
     var left = node.left;
     if (t.isVariableDeclaration(left)) {
       var declar = left.declarations[0];
       if (declar.init) throw file.errorWithNode(declar, messages.get("noAssignmentsInForHead"));
     }
-}
+  },
 
-export { ForOfStatement as ForInStatement };
-
-export function MethodDefinition(node) {
+  MethodDefinition(node) {
     if (node.kind !== "constructor") {
       // get constructor() {}
       var isConstructor = !node.computed && t.isIdentifier(node.key, { name: "constructor" });
@@ -28,10 +27,10 @@ export function MethodDefinition(node) {
       }
     }
 
-  Property.apply(this, arguments);
-}
+    visitor.Property.apply(this, arguments);
+  },
 
-export function Property(node, parent, scope, file) {
+  Property(node, parent, scope, file) {
     if (node.kind === "set") {
       if (node.value.params.length !== 1) {
         throw file.errorWithNode(node.value, messages.get("settersInvalidParamLength"));
@@ -42,4 +41,5 @@ export function Property(node, parent, scope, file) {
         throw file.errorWithNode(first, messages.get("settersNoRest"));
       }
     }
-}
+  }
+};

src/babel/transformation/transformers/minification/constant-folding.js

@@ -6,7 +6,8 @@ export var metadata = {
   experimental: true
 };
 
-export function AssignmentExpression() {
+export var visitor = {
+  AssignmentExpression() {
     var left = this.get("left");
     if (!left.isIdentifier()) return;
 
@@ -19,9 +20,9 @@ export function AssignmentExpression() {
     } else {
       binding.deoptValue();
     }
-}
+  },
 
-export function IfStatement() {
+  IfStatement() {
     var evaluated = this.get("test").evaluate();
     if (!evaluated.confident) {
       // todo: deopt binding values for constant violations inside
@@ -33,9 +34,9 @@ export function IfStatement() {
     } else {
       this.skipKey("consequent");
     }
-}
+  },
 
-export var Scopable = {
+  Scopable: {
     enter() {
       var funcScope = this.scope.getFunctionParent();
 
@@ -61,11 +62,12 @@ export var Scopable = {
         binding.clearValue();
       }
     }
-};
+  },
 
-export var Expression = {
+  Expression: {
     exit() {
       var res = this.evaluate();
       if (res.confident) return t.valueToNode(res.value);
     }
+  }
 };

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

@@ -23,7 +23,8 @@ export var metadata = {
   experimental: true
 };
 
-export function ReferencedIdentifier(node, parent, scope) {
+export var visitor = {
+  ReferencedIdentifier(node, parent, scope) {
     var binding = scope.getBinding(node.name);
     if (!binding || binding.references > 1 || !binding.constant) return;
     if (binding.kind === "param" || binding.kind === "module") return;
@@ -52,32 +53,30 @@ export function ReferencedIdentifier(node, parent, scope) {
     scope.removeBinding(node.name);
     binding.path.dangerouslyRemove();
     return replacement;
-}
+  },
 
-export function FunctionDeclaration(node, parent, scope) {
-  var bindingInfo = scope.getBinding(node.id.name);
-  if (bindingInfo && !bindingInfo.referenced) {
+  "ClassDeclaration|FunctionDeclaration"(node, parent, scope) {
+    var binding = scope.getBinding(node.id.name);
+    if (binding && !binding.referenced) {
       this.dangerouslyRemove();
     }
-}
+  },
 
-export { FunctionDeclaration as ClassDeclaration };
-
-export function VariableDeclarator(node, parent, scope) {
+  VariableDeclarator(node, parent, scope) {
     if (!t.isIdentifier(node.id) || !scope.isPure(node.init, true)) return;
-  FunctionDeclaration.apply(this, arguments);
-}
+    visitor["ClassDeclaration|FunctionDeclaration"].apply(this, arguments);
+  },
 
-export function ConditionalExpression(node, parent, scope) {
+  ConditionalExpression(node) {
     var evaluateTest = this.get("test").evaluateTruthy();
     if (evaluateTest === true) {
       return node.consequent;
     } else if (evaluateTest === false) {
       return node.alternate;
     }
-}
+  },
 
-export function BlockStatement(node) {
+  BlockStatement() {
     var paths = this.get("body");
 
     var purge = false;
@@ -94,9 +93,9 @@ export function BlockStatement(node) {
         path.dangerouslyRemove();
       }
     }
-}
+  },
 
-export var IfStatement = {
+  IfStatement: {
     exit(node) {
       var consequent = node.consequent;
       var alternate  = node.alternate;
@@ -151,4 +150,5 @@ export var IfStatement = {
         node.test       = t.unaryExpression("!", test, true);
       }
     }
+  }
 };

src/babel/transformation/transformers/minification/member-expression-literals.js

@@ -5,7 +5,8 @@ export var metadata = {
   group: "builtin-trailing"
 };
 
-export var MemberExpression = {
+export var visitor = {
+  MemberExpression: {
     exit(node) {
       var prop = node.property;
       if (node.computed && t.isLiteral(prop) && t.isValidIdentifier(prop.value)) {
@@ -14,4 +15,5 @@ export var MemberExpression = {
         node.computed = false;
       }
     }
+  }
 };

src/babel/transformation/transformers/minification/property-literals.js

@@ -5,7 +5,8 @@ export var metadata = {
   group: "builtin-trailing"
 };
 
-export var Property = {
+export var visitor = {
+  Property: {
     exit(node) {
       var key = node.key;
       if (t.isLiteral(key) && t.isValidIdentifier(key.value)) {
@@ -14,4 +15,5 @@ export var Property = {
         node.computed = false;
       }
     }
+  }
 };

src/babel/transformation/transformers/minification/remove-console.js

@@ -3,8 +3,10 @@ export var metadata = {
   group: "builtin-pre"
 };
 
-export function CallExpression(node, parent) {
+export var visitor = {
+  CallExpression() {
     if (this.get("callee").matchesPattern("console", true)) {
       this.dangerouslyRemove();
     }
-}
+  }
+};

src/babel/transformation/transformers/minification/remove-debugger.js

@@ -3,6 +3,8 @@ export var metadata = {
   group: "builtin-pre"
 };
 
-export function DebuggerStatement(node) {
+export var visitor = {
+  DebuggerStatement() {
     this.dangerouslyRemove();
-}
+  }
+};

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

@@ -4,8 +4,10 @@ export var metadata = {
   optional: true
 };
 
-export function ForOfStatement(node, parent, scope, file) {
+export var visitor = {
+  ForOfStatement(node, parent, scope, file) {
     if (this.get("right").isGenericType("Array")) {
       return _ForOfStatementArray.call(this, node, scope, file);
     }
-}
+  }
+};

src/babel/transformation/transformers/optimisation/react.constant-elements.js

@@ -26,7 +26,8 @@ var immutabilityVisitor = {
   }
 };
 
-export function JSXElement(node, parent, scope, file) {
+export var visitor = {
+  JSXElement(node) {
     if (node._hoisted) return;
 
     var state = { isImmutable: true };
@@ -37,4 +38,5 @@ export function JSXElement(node, parent, scope, file) {
     } else {
       node._hoisted = true;
     }
-}
+  }
+};

src/babel/transformation/transformers/optimisation/react.inline-elements.js

@@ -18,7 +18,8 @@ function isJSXAttributeOfName(attr, name) {
   return t.isJSXAttribute(attr) && t.isJSXIdentifier(attr.name, { name: name });
 }
 
-export function JSXElement(node, parent, scope, file) {
+export var visitor = {
+  JSXElement(node, parent, scope, file) {
     // filter
     var open = node.openingElement;
     if (hasRefOrSpread(open.attributes)) return;
@@ -71,4 +72,5 @@ export function JSXElement(node, parent, scope, file) {
     pushElemProp("key", key);
 
     return obj;
-}
+  }
+};

src/babel/transformation/transformers/other/async-to-generator.js

@@ -7,8 +7,10 @@ export var metadata = {
   dependencies: ["es7.asyncFunctions", "es6.classes"]
 };
 
-export function Func/*tion*/(node, parent, scope, file) {
+export var visitor = {
+  Function(node, parent, scope, file) {
     if (!node.async || node.generator) return;
 
     return remapAsyncToGenerator(this, file.addHelper("async-to-generator"));
-}
+  }
+};

src/babel/transformation/transformers/other/bluebird-coroutines.js

@@ -10,11 +10,13 @@ export var metadata = {
   dependencies: ["es7.asyncFunctions", "es6.classes"]
 };
 
-export function Func/*tion*/(node, parent, scope, file) {
+export var visitor = {
+  Function(node, parent, scope, file) {
     if (!node.async || node.generator) return;
 
     return remapAsyncToGenerator(
       this,
       t.memberExpression(file.addImport("bluebird", null, "absolute"), t.identifier("coroutine"))
     );
-}
+  }
+};

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

@@ -6,7 +6,8 @@ export var metadata = {
   optional: true
 };
 
-export function CallExpression(node) {
+export var visitor = {
+  CallExpression(node) {
     if (this.get("callee").isIdentifier({ name: "eval" }) && node.arguments.length === 1) {
       var evaluate = this.get("arguments")[0].evaluate();
       if (!evaluate.confident) return;
@@ -18,4 +19,5 @@ export function CallExpression(node) {
       traverse.removeProperties(ast);
       return ast.program;
     }
-}
+  }
+};

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

@@ -4,37 +4,39 @@ export var metadata = {
   group: "builtin-trailing"
 };
 
-export function Flow(node) {
+export var visitor = {
+  Flow() {
     this.dangerouslyRemove();
-}
+  },
 
-export function ClassProperty(node) {
+  ClassProperty(node) {
     node.typeAnnotation = null;
     if (!node.value) this.dangerouslyRemove();
-}
+  },
 
-export function Class(node) {
+  Class(node) {
     node.implements = null;
-}
+  },
 
-export function Func/*tion*/(node) {
+  Function(node) {
     for (var i = 0; i < node.params.length; i++) {
       var param = node.params[i];
       param.optional = false;
     }
-}
+  },
 
-export function TypeCastExpression(node) {
+  TypeCastExpression(node) {
     do {
       node = node.expression;
     } while(t.isTypeCastExpression(node));
     return node;
-}
+  },
 
-export function ImportDeclaration(node) {
+  ImportDeclaration(node) {
     if (node.isType) this.dangerouslyRemove();
-}
+  },
 
-export function ExportDeclaration(node) {
+  ExportDeclaration() {
     if (this.get("declaration").isTypeAlias()) this.dangerouslyRemove();
-}
+  }
+};

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

@@ -5,7 +5,8 @@ export var metadata = {
   optional: true
 };
 
-export var FunctionExpression = {
+export var visitor = {
+  FunctionExpression: {
     exit(node) {
       if (!node.id) return;
       node._ignoreUserWhitespace = true;
@@ -18,4 +19,5 @@ export var FunctionExpression = {
         []
       );
     }
+  }
 };

src/babel/transformation/transformers/other/react-compat.js

@@ -10,7 +10,7 @@ export var metadata = {
   group: "builtin-advanced"
 };
 
-require("../../helpers/build-react-transformer")(exports, {
+export var visitor = require("../../helpers/build-react-transformer")({
   pre(state) {
     state.callee = state.tagExpr;
   },

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

@@ -7,7 +7,24 @@ export var metadata = {
   group: "builtin-advanced"
 };
 
-export function Program(node, parent, scope, file) {
+export var visitor = require("../../helpers/build-react-transformer")({
+  pre(state) {
+    var tagName = state.tagName;
+    var args    = state.args;
+    if (react.isCompatTag(tagName)) {
+      args.push(t.literal(tagName));
+    } else {
+      args.push(state.tagExpr);
+    }
+  },
+
+  post(state, file) {
+    state.callee = file.get("jsxIdentifier");
+  }
+});
+
+
+visitor.Program = function (node, parent, scope, file) {
   var id = file.opts.jsxPragma;
 
   for (var i = 0; i < file.ast.comments.length; i++) {
@@ -26,20 +43,4 @@ export function Program(node, parent, scope, file) {
   file.set("jsxIdentifier", id.split(".").map(t.identifier).reduce(function (object, property) {
     return t.memberExpression(object, property);
   }));
-}
-
-require("../../helpers/build-react-transformer")(exports, {
-  pre(state) {
-    var tagName = state.tagName;
-    var args    = state.args;
-    if (react.isCompatTag(tagName)) {
-      args.push(t.literal(tagName));
-    } else {
-      args.push(state.tagExpr);
-    }
-  },
-
-  post(state, file) {
-    state.callee = file.get("jsxIdentifier");
-  }
-});
+};

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

@@ -6,7 +6,8 @@ export var metadata = {
   group: "builtin-advanced"
 };
 
-export var Func/*tion*/ = {
+export var visitor = {
+  Function: {
     exit(node) {
       if (node.async || node.generator) {
         // Although this code transforms only the subtree rooted at the given
@@ -19,6 +20,7 @@ export var Func/*tion*/ = {
         regenerator.transform(convertNodePath(this));
       }
     }
+  }
 };
 
 // Given a Babel NodePath, return an ast-types NodePath that includes full

src/babel/transformation/transformers/other/runtime/index.js

@@ -19,7 +19,8 @@ export function pre(file) {
   });
 }
 
-export function ReferencedIdentifier(node, parent, scope, file) {
+export var visitor = {
+  ReferencedIdentifier(node, parent, scope, file) {
     if (node.name === "regeneratorRuntime") {
       return file.get("regeneratorIdentifier");
     }
@@ -31,9 +32,9 @@ export function ReferencedIdentifier(node, parent, scope, file) {
     // Symbol() -> _core.Symbol(); new Promise -> new _core.Promise
     var modulePath = definitions.builtins[node.name];
     return file.addImport(`${RUNTIME_MODULE_NAME}/core-js/${modulePath}`, node.name, "absoluteDefault");
-}
+  },
 
-export function CallExpression(node, parent, scope, file) {
+  CallExpression(node, parent, scope, file) {
     // arr[Symbol.iterator]() -> _core.$for.getIterator(arr)
 
     if (node.arguments.length) return;
@@ -44,9 +45,9 @@ export function CallExpression(node, parent, scope, file) {
     if (!this.get("callee.property").matchesPattern("Symbol.iterator")) return;
 
     return t.callExpression(file.addImport(`${RUNTIME_MODULE_NAME}/core-js/get-iterator`, "getIterator", "absoluteDefault"), [callee.object]);
-}
+  },
 
-export function BinaryExpression(node, parent, scope, file) {
+  BinaryExpression(node, parent, scope, file) {
     // Symbol.iterator in arr -> core.$for.isIterable(arr)
 
     if (node.operator !== "in") return;
@@ -56,9 +57,9 @@ export function BinaryExpression(node, parent, scope, file) {
       file.addImport(`${RUNTIME_MODULE_NAME}/core-js/is-iterable`, "isIterable", "absoluteDefault"),
       [node.right]
     );
-}
+  },
 
-export var MemberExpression = {
+  MemberExpression: {
     enter(node, parent, scope, file) {
       // Array.from -> _core.Array.from
 
@@ -97,4 +98,5 @@ export var MemberExpression = {
         prop
       );
     }
+  }
 };

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

@@ -6,7 +6,8 @@ export var metadata = {
 
 const THIS_BREAK_KEYS = ["FunctionExpression", "FunctionDeclaration", "ClassExpression", "ClassDeclaration"];
 
-export var Program = {
+export var visitor = {
+  Program: {
     enter(program) {
       var first = program.body[0];
 
@@ -23,10 +24,11 @@ export var Program = {
       }
       directive._blockHoist = Infinity;
     }
-};
+  },
 
-export function ThisExpression() {
+  ThisExpression() {
     if (!this.findParent((path) => !path.is("shadow") && THIS_BREAK_KEYS.indexOf(path.type) >= 0)) {
       return t.identifier("undefined");
     }
-}
+  }
+};

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

@@ -23,14 +23,16 @@ function statementList(key, path) {
   }
 }
 
-export function BlockStatement(node, parent) {
+export var visitor = {
+  BlockStatement(node, parent) {
     if ((t.isFunction(parent) && parent.body === node) || t.isExportDeclaration(parent)) {
       return;
     }
 
     statementList("body", this);
-}
+  },
 
-export function SwitchCase() {
+  SwitchCase() {
     statementList("consequent", this);
-}
+  }
+};

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

@@ -4,8 +4,8 @@ export var metadata = {
   group: "builtin-pre"
 };
 
-export var FunctionExpression = {
+export var visitor = {
+  "ArrowFunctionExpression|FunctionExpression": {
     exit: bare
+  }
 };
-
-export { FunctionExpression as ArrowFunctionExpression };

src/babel/transformation/transformers/spec/proto-to-assign.js

@@ -19,7 +19,8 @@ export var metadata = {
   optional: true
 };
 
-export function AssignmentExpression(node, parent, scope, file) {
+export var visitor = {
+  AssignmentExpression(node, parent, scope, file) {
     if (!isProtoAssignmentExpression(node)) return;
 
     var nodes = [];
@@ -31,18 +32,18 @@ export function AssignmentExpression(node, parent, scope, file) {
     if (temp) nodes.push(temp);
 
     return nodes;
-}
+  },
 
-export function ExpressionStatement(node, parent, scope, file) {
+  ExpressionStatement(node, parent, scope, file) {
     var expr = node.expression;
     if (!t.isAssignmentExpression(expr, { operator: "=" })) return;
 
     if (isProtoAssignmentExpression(expr)) {
       return buildDefaultsCallExpression(expr, expr.left.object, file);
     }
-}
+  },
 
-export function ObjectExpression(node, parent, scope, file) {
+  ObjectExpression(node, parent, scope, file) {
     var proto;
 
     for (var i = 0; i < node.properties.length; i++) {
@@ -59,4 +60,5 @@ export function ObjectExpression(node, parent, scope, file) {
       if (node.properties.length) args.push(node);
       return t.callExpression(file.addHelper("extends"), args);
     }
-}
+  }
+};

src/babel/transformation/transformers/spec/undefined-to-void.js

@@ -1,12 +0,0 @@
-import * as t from "../../../types";
-
-export var metadata = {
-  optional: true,
-  react: true
-};
-
-export function Identifier(node, parent) {
-  if (node.name === "undefined" && this.isReferenced()) {
-    return t.unaryExpression("void", t.literal(0), true);
-  }
-}

src/babel/transformation/transformers/utility/inline-environment-variables.js

@@ -7,11 +7,13 @@ export var metadata = {
 
 var match = t.buildMatchMemberExpression("process.env");
 
-export function MemberExpression(node) {
+export var visitor = {
+  MemberExpression(node) {
     if (match(node.object)) {
       var key = this.toComputedKey();
       if (t.isLiteral(key)) {
         return t.valueToNode(process.env[key.value]);
       }
     }
-}
+  }
+};

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

@@ -13,12 +13,14 @@ function check(source, file) {
   }
 }
 
-export function CallExpression(node, parent, scope, file) {
+export var visitor = {
+  CallExpression(node, parent, scope, file) {
     if (this.get("callee").isIdentifier({ name: "require" }) && node.arguments.length === 1) {
       check(node.arguments[0], file);
     }
-}
+  },
 
-export function ModuleDeclaration(node, parent, scope, file) {
+  ModuleDeclaration(node, parent, scope, file) {
     check(node.source, file);
-}
+  }
+};

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

@@ -5,7 +5,8 @@ export var metadata = {
   optional: true
 };
 
-export function ReferencedIdentifier(node, parent, scope, file) {
+export var visitor = {
+  ReferencedIdentifier(node, parent, scope) {
     var binding = scope.getBinding(node.name);
     if (binding && binding.kind === "type" && !this.parentPath.isFlow()) {
       throw this.errorWithNode(messages.get("undeclaredVariableType", node.name), ReferenceError);
@@ -40,4 +41,5 @@ export function ReferencedIdentifier(node, parent, scope, file) {
     //
 
     throw this.errorWithNode(msg, ReferenceError);
-}
+  }
+};

src/babel/traversal/index.js

@@ -15,7 +15,6 @@ export default function traverse(parent, opts, scope, state, parentPath) {
 
   if (!opts) opts = {};
 
-  visitors.verify(opts);
   visitors.explode(opts);
 
   // array of nodes

src/babel/traversal/path/lib/hoister.js

@@ -8,17 +8,17 @@ var referenceVisitor = {
     }
 
     // direct references that we need to track to hoist this to the highest scope we can
-    var bindingInfo = scope.getBinding(node.name);
-    if (!bindingInfo) return;
+    var binding = scope.getBinding(node.name);
+    if (!binding) return;
 
     // this binding isn't accessible from the parent scope so we can safely ignore it
     // eg. it's in a closure etc
-    if (bindingInfo !== state.scope.getBinding(node.name)) return;
+    if (binding !== state.scope.getBinding(node.name)) return;
 
-    if (bindingInfo.constant) {
-      state.bindings[node.name] = bindingInfo;
+    if (binding.constant) {
+      state.bindings[node.name] = binding;
     } else {
-      for (var violationPath of (bindingInfo.constantViolations: Array)) {
+      for (var violationPath of (binding.constantViolations: Array)) {
         state.breakOnScopePaths.push(violationPath.scope.path);
       }
     }

src/babel/traversal/scope/index.js

@@ -31,9 +31,9 @@ var collectorVisitor = {
   },
 
   ReferencedIdentifier(node) {
-    var bindingInfo = this.scope.getBinding(node.name);
-    if (bindingInfo) {
-      bindingInfo.reference();
+    var binding = this.scope.getBinding(node.name);
+    if (binding) {
+      binding.reference(this);
     } else {
       this.scope.getProgramParent().addGlobal(node);
     }

src/babel/traversal/visitors.js

@@ -8,6 +8,24 @@ export function explode(visitor) {
   if (visitor._exploded) return visitor;
   visitor._exploded = true;
 
+  // normalise pipes
+  for (let nodeType in visitor) {
+    if (shouldIgnoreKey(nodeType)) continue;
+
+    let parts = nodeType.split("|");
+    if (parts.length === 1) continue;
+
+    let fns = visitor[nodeType];
+    delete visitor[nodeType];
+
+    for (let part of (parts: Array)) {
+      visitor[part] = fns;
+    }
+  }
+
+  // verify data structure
+  verify(visitor);
+
   // make sure there's no __esModule type since this is because we're using loose mode
   // and it sets __esModule to be enumerable on all modules :(
   delete visitor.__esModule;
@@ -21,6 +39,7 @@ export function explode(visitor) {
   // ensure visitors are objects
   ensureEntranceObjects(visitor);
 
+  // ensure enter/exit callbacks are arrays
   ensureCallbackArrays(visitor);
 
   // add type wrappers

src/babel/types/index.js

@@ -312,7 +312,6 @@ export function inherits(child: Object, parent: Object): Object {
 toFastProperties(t);
 toFastProperties(t.VISITOR_KEYS);
 
-exports.__esModule = true;
 assign(t, require("./retrievers"));
 assign(t, require("./validators"));
 assign(t, require("./converters"));

test/core/path.js

@@ -1,5 +1,5 @@
-var Transformer = require("../../lib/babel/transformation/transformer");
 var transform = require("../../lib/babel/transformation");
+var Plugin    = require("../../lib/babel/transformation/plugin");
 var babel     = require("../../lib/babel/api/node");
 var chai      = require("chai");
 
@@ -9,7 +9,7 @@ suite("traversal path", function () {
 
     var actualCode = transform(expectCode, {
       blacklist: "strict",
-      plugins: [new Transformer("foobar", {
+      plugins: [new Plugin("foobar", {
         FunctionDeclaration: function () {
           return "console.whatever()";
         }