v5.3.1

Add failing tests that document ES 6 generators bug

.gitmodules

@@ -1,6 +1,3 @@
 [submodule "vendor/traceur"]
 	path = vendor/traceur
 	url = https://github.com/google/traceur-compiler
-[submodule "vendor/compat-table"]
-	path = vendor/compat-table
-	url = https://github.com/kangax/compat-table

CHANGELOG.md

@@ -13,6 +13,41 @@ _Note: Gaps between patch versions are faulty/broken releases._
 
 See [CHANGELOG - 6to5](CHANGELOG-6to5.md) for the pre-4.0.0 version changelog.
 
+## 5.3.1
+
+ * **Bug Fix**
+  * Fix unique export specifiers not being cloned when exploding class and function exports,
+ * **Polish**
+  * Turn import remaps to sequence expressions to remove their context and improve performance.
+
+## 5.3.0
+
+**Speeeeeeed**
+
+![gifs lol](https://31.media.tumblr.com/568205a0e37ae15eca510fa639589a59/tumblr_n8kw8kpcSb1sg6cg8o1_500.gif)
+
+ * **Spec Compliancy**
+  * Allow trailing param commas for methods when using the `es7.trailingCommas` transformer.
+ * **Bug Fix**
+  * Fix `es6.blockScoping` transformer not properly ignoring `break` in `SwitchCase`.
+  * Fix lookahead context saving to avoid weird tokenizer state.
+  * Explode duplicate identifiers in export/import specifiers and property shorthand to create unique objects.
+  * Skip loose mode for class methods when they have decorators.
+  * When removing nodes, share their comments with their siblings.
+  * Properly hoist temp param declarations when doing TCO.
+ * **Internal**
+  * Add `--harmony_generators` flag to `$ babel-node`.
+ * **Polish**
+  * Move many `utility` transformers to `minification`.
+
+## 5.2.17
+
+ * **Bug Fix**
+  * Fix auxiliary comments not properly being attached to function declaration helpers.
+  * Add `Super` node type to `ast-types` patch.
+  * Ignore parameter bindings when attempting to inline them in the `minification.deadCodeElimination` transformer.
+  * Correct `extensions` arguments when using the Babel CLI.
+
 ## 5.2.16
 
  * **Bug Fix**

Makefile

@@ -122,5 +122,4 @@ bootstrap:
 	npm link
 	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

@@ -1,9 +1,10 @@
 {
   "name": "babel-core",
   "description": "Turn ES6 code into readable vanilla ES5 with source maps",
-  "version": "5.2.16",
+  "version": "5.3.1",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
+  "license": "MIT",
   "repository": "babel/babel",
   "main": "lib/babel/api/node.js",
   "browser": {
@@ -63,7 +64,7 @@
     "user-home": "^1.1.1"
   },
   "devDependencies": {
-    "babel": "5.1.13",
+    "babel": "5.3.0",
     "browserify": "^9.0.8",
     "chai": "^2.2.0",
     "eslint": "^0.18.0",

packages/babel-cli/bin/babel-node

@@ -56,6 +56,7 @@ babelArgs.forEach(function(arg){
     case "--harmony_object_literals":
     case "--harmony_templates":
     case "--harmony_rest_parameters":
+    case "--harmony_generators":
     case "--compiled_keyed_generic_loads":
     case "--pretenuring_call_new":
     case "--allocation_site_pretenuring":

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

@@ -30,7 +30,7 @@ module.exports = function (commander, filenames, opts) {
   var handleFile = function (src, filename) {
     if (util.shouldIgnore(src)) return;
 
-    if (util.canCompile(filename, opts.extensions)) {
+    if (util.canCompile(filename, commander.extensions)) {
       write(src, filename);
     } else if (commander.copyFiles) {
       outputFileSync(path.join(commander.outDir, filename), fs.readFileSync(src));

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

@@ -70,6 +70,12 @@ commander.parse(process.argv);
 
 //
 
+if (commander.extensions) {
+  commander.extensions = util.arrayify(commander.extensions);
+}
+
+//
+
 var errors = [];
 
 var filenames = commander.args.reduce(function (globbed, input) {

packages/babel-cli/package.json

@@ -1,13 +1,13 @@
 {
   "name": "babel",
   "description": "Turn ES6 code into readable vanilla ES5 with source maps",
-  "version": "5.2.15",
+  "version": "5.3.0",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
   "repository": "babel/babel",
   "preferGlobal": true,
   "dependencies": {
-    "babel-core": "^5.2.15",
+    "babel-core": "^5.3.0",
     "chokidar": "^1.0.0",
     "commander": "^2.6.0",
     "convert-source-map": "^1.1.0",

packages/babel-runtime/package.json

@@ -1,7 +1,7 @@
 {
   "name": "babel-runtime",
   "description": "babel selfContained runtime",
-  "version": "5.2.15",
+  "version": "5.3.0",
   "repository": "babel/babel",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "dependencies": {

src/acorn/plugins/flow.js

@@ -153,10 +153,15 @@ pp.flow_parseTypeAlias = function (node) {
     node.typeParameters = null
   }
 
+  var oldInType = this.inType;
+  this.inType = true;
+
   this.expect(tt.eq)
 
   node.right = this.flow_parseType()
 
+  this.inType = oldInType;
+
   this.semicolon()
 
   return this.finishNode(node, "TypeAlias")

src/acorn/src/expression.js

@@ -474,7 +474,10 @@ pp.parseNew = function() {
   }
   let start = this.markPosition()
   node.callee = this.parseSubscripts(this.parseExprAtom(), start, true)
-  if (this.eat(tt.parenL)) node.arguments = this.parseExprList(tt.parenR, false)
+  if (this.eat(tt.parenL)) node.arguments = this.parseExprList(
+    tt.parenR,
+    this.options.features["es7.trailingFunctionCommas"]
+  )
   else node.arguments = empty
   return this.finishNode(node, "NewExpression")
 }
@@ -632,7 +635,7 @@ pp.parseMethod = function(isGenerator, isAsync) {
   let node = this.startNode()
   this.initFunction(node, isAsync)
   this.expect(tt.parenL)
-  node.params = this.parseBindingList(tt.parenR, false, false)
+  node.params = this.parseBindingList(tt.parenR, false, this.options.features["es7.trailingFunctionCommas"])
   if (this.options.ecmaVersion >= 6) {
     node.generator = isGenerator
   }

src/acorn/src/lookahead.js

@@ -14,7 +14,11 @@ var STATE_KEYS = [
   "pos",
   "end",
   "type",
-  "value"
+  "value",
+  "exprAllowed",
+  "potentialArrowAt",
+  "currLine",
+  "input"
 ];
 
 pp.getState = function () {
@@ -23,6 +27,7 @@ pp.getState = function () {
     var key = STATE_KEYS[i]
     state[key] = this[key]
   }
+  state.context = this.context.slice()
   return state
 };
 

src/acorn/src/tokenize.js

@@ -283,7 +283,7 @@ pp.readToken_lt_gt = function(code) { // '<>'
   }
   if (next == 33 && code == 60 && this.input.charCodeAt(this.pos + 2) == 45 &&
       this.input.charCodeAt(this.pos + 3) == 45) {
-    if (this.inModule) unexpected()
+    if (this.inModule) this.unexpected()
     // `<!--`, an XML-style comment that should be interpreted as a line comment
     this.skipLineComment(4)
     this.skipSpace()

src/babel/generation/generators/jsx.js

@@ -43,13 +43,13 @@ export function JSXElement(node, print) {
   if (open.selfClosing) return;
 
   this.indent();
-  each(node.children, (child) => {
+  for (var child of (node.children: Array)) {
     if (t.isLiteral(child)) {
       this.push(child.value, true);
     } else {
       print(child);
     }
-  });
+  }
   this.dedent();
 
   print(node.closingElement);

src/babel/generation/generators/modules.js

@@ -3,7 +3,7 @@ import * as t from "../../types";
 
 export function ImportSpecifier(node, print) {
   print(node.imported);
-  if (node.local && node.local !== node.imported) {
+  if (node.local && node.local.name !== node.imported.name) {
     this.push(" as ");
     print(node.local);
   }
@@ -19,7 +19,7 @@ export function ExportDefaultSpecifier(node, print) {
 
 export function ExportSpecifier(node, print) {
   print(node.local);
-  if (node.exported && node.local !== node.exported) {
+  if (node.exported && node.local.name !== node.exported.name) {
     this.push(" as ");
     print(node.exported);
   }

src/babel/generation/generators/statements.js

@@ -182,8 +182,8 @@ export function VariableDeclaration(node, print, parent) {
   var hasInits = false;
   // don't add whitespace to loop heads
   if (!t.isFor(parent)) {
-    for (var i = 0; i < node.declarations.length; i++) {
-      if (node.declarations[i].init) {
+    for (var declar of (node.declarations: Array)) {
+      if (declar.init) {
         // has an init so let's split it up over multiple lines
         hasInits = true;
       }
@@ -191,7 +191,7 @@ export function VariableDeclaration(node, print, parent) {
   }
 
   var sep = ",";
-  if (!this.format.compact && hasInits && !this.format.retainLines) {
+  if (!this.format.compact && !this.format.concise && hasInits && !this.format.retainLines) {
     sep += `\n${repeating(" ", node.kind.length + 1)}`;
   } else {
     sep += " ";

src/babel/generation/generators/template-literals.js

@@ -15,15 +15,15 @@ export function TemplateLiteral(node, print) {
   var quasis = node.quasis;
   var len    = quasis.length;
 
-  each(quasis, (quasi, i) => {
-    print(quasi);
+  for (var i = 0; i < len; i++) {
+    print(quasis[i]);
 
     if (i + 1 < len) {
       this.push("${ ");
       print(node.expressions[i]);
       this.push(" }");
     }
-  });
+  }
 
   this._push("`");
 }

src/babel/generation/generators/types.js

@@ -1,4 +1,5 @@
 import each from "lodash/collection/each";
+import * as t from "../../types";
 
 export function Identifier(node) {
   this.push(node.name);
@@ -39,7 +40,14 @@ export function Property(node, print) {
       this.push("]");
     } else {
       print(node.key);
-      if (node.shorthand) return;
+
+      // shorthand!
+      if (node.shorthand &&
+        (t.isIdentifier(node.key) &&
+         t.isIdentifier(node.value) &&
+         node.key.name === node.value.name)) {
+        return;
+      }
     }
 
     this.push(":");
@@ -54,7 +62,8 @@ export function ArrayExpression(node, print) {
 
   this.push("[");
 
-  each(elems, (elem, i) => {
+  for (var i = 0; i < elems.length; i++) {
+    var elem = elems[i];
     if (!elem) {
       // If the array expression ends with a hole, that hole
       // will be ignored by the interpreter, but if it ends with
@@ -67,7 +76,7 @@ export function ArrayExpression(node, print) {
       print(elem);
       if (i < len - 1) this.push(",");
     }
-  });
+  }
 
   this.push("]");
 }

src/babel/generation/index.js

@@ -105,11 +105,13 @@ class CodeGenerator {
 
     this.print(ast);
 
-    var comments = [];
-    each(ast.comments, function (comment) {
-      if (!comment._displayed) comments.push(comment);
-    });
-    this._printComments(comments);
+    if (ast.comments) {
+      var comments = [];
+      for (var comment of (ast.comments: Array)) {
+        if (!comment._displayed) comments.push(comment);
+      }
+      this._printComments(comments);
+    }
 
     return {
       map:  this.map.get(),
@@ -249,7 +251,8 @@ class CodeGenerator {
 
     if (opts.indent) this.indent();
 
-    each(nodes, (node, i) => {
+    for (var i = 0; i < nodes.length; i++) {
+      var node = nodes[i];
       print(node, {
         statement: opts.statement,
         addNewlines: opts.addNewlines,
@@ -263,7 +266,7 @@ class CodeGenerator {
           }
         }
       });
-    });
+    }
 
     if (opts.indent) this.dedent();
   }
@@ -314,9 +317,9 @@ class CodeGenerator {
       nodes.push(node.argument);
     }
 
-    each(nodes, (node) => {
+    for (var node of (nodes: Array)) {
       comments = comments.concat(this._getComments(key, node));
-    });
+    }
 
     return comments;
   }
@@ -331,19 +334,21 @@ class CodeGenerator {
     if (!this.format.comments) return;
     if (!comments || !comments.length) return;
 
-    each(comments, (comment) => {
+    for (var comment of (comments: Array)) {
       var skip = false;
 
-      // find the original comment in the ast and set it as displayed
-      each(this.ast.comments, function (origComment) {
-        if (origComment.start === comment.start) {
-          // comment has already been output
-          if (origComment._displayed) skip = true;
+      if (this.ast.comments) {
+        // find the original comment in the ast and set it as displayed
+        for (var origComment of (this.ast.comments: Array)) {
+          if (origComment.start === comment.start) {
+            // comment has already been output
+            if (origComment._displayed) skip = true;
 
-          origComment._displayed = true;
-          return false;
+            origComment._displayed = true;
+            break;
+          }
         }
-      });
+      }
 
       if (skip) return;
 
@@ -387,7 +392,7 @@ class CodeGenerator {
 
       // whitespace after
       this.newline(this.whitespace.getNewlinesAfter(comment));
-    });
+    }
   }
 }
 

src/babel/messages.js

@@ -18,7 +18,6 @@ export const MESSAGES = {
   modulesIllegalExportName: "Illegal export $1",
   unknownForHead: "Unknown node type $1 in ForStatement",
   didYouMean: "Did you mean $1?",
-  evalInStrictMode: "eval is not allowed in strict mode",
   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",
@@ -26,7 +25,6 @@ export const MESSAGES = {
 
   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: "You passed \`traverse()\` a visitor object with the key $1 that's a `Function` instead of `{ enter: Function }`. You need to normalise your visitor with `traverse.explode(visitor)`.",
   traverseVerifyVisitorProperty: "You passed `traverse()` a visitor object with the property $1 that has the invalid property $2",
   traverseVerifyNodeType: "You gave us a visitor for the node type $1 but it's not a valid type",
 

src/babel/patch.js

@@ -33,6 +33,9 @@ def("DoExpression")
   .build("body")
   .field("body", [def("Statement")]);
 
+def("Super")
+  .bases("Expression");
+
 def("ExportDefaultDeclaration")
   .bases("Declaration")
   .build("declaration")

src/babel/transformation/file/index.js

@@ -4,6 +4,7 @@ import moduleFormatters from "../modules";
 import PluginManager from "./plugin-manager";
 import shebangRegex from "shebang-regex";
 import TraversalPath from "../../traversal/path";
+import Transformer from "../transformer";
 import isFunction from "lodash/lang/isFunction";
 import isAbsolute from "path-is-absolute";
 import resolveRc from "../../tools/resolve-rc";
@@ -23,24 +24,12 @@ 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 = {
-  exit(node, parent, scope, state) {
-    checkPath(state.stack, this);
-  }
-};
-
-function checkPath(stack, path) {
-  each(stack, function (pass) {
-    if (pass.shouldRun || pass.ran) return;
-    pass.checkPath(path);
-  });
-}
-
 export default class File {
   constructor(opts = {}, pipeline) {
+    this.transformerDependencies = {};
+
     this.dynamicImportTypes = {};
     this.dynamicImportIds   = {};
     this.dynamicImports     = [];
@@ -49,7 +38,6 @@ export default class File {
     this.usedHelpers  = {};
     this.dynamicData  = {};
     this.data         = {};
-    this.uids         = {};
 
     this.pipeline = pipeline;
     this.log      = new Logger(this, opts.filename || "unknown");
@@ -96,10 +84,7 @@ export default class File {
     "interop-require",
   ];
 
-  static soloHelpers = [
-    "ludicrous-proxy-create",
-    "ludicrous-proxy-directory"
-  ];
+  static soloHelpers = [];
 
   static options = require("./options");
 
@@ -203,7 +188,8 @@ export default class File {
     var stack = [];
 
     // build internal transformers
-    each(this.pipeline.transformers, function (transformer, key) {
+    for (var key in this.pipeline.transformers) {
+      var transformer = this.pipeline.transformers[key];
       var pass = transformers[key] = transformer.buildPass(file);
 
       if (pass.canTransform()) {
@@ -217,7 +203,7 @@ export default class File {
           transformer.manipulateOptions(file.opts, file);
         }
       }
-    });
+    }
 
     // init plugins!
     var beforePlugins = [];
@@ -233,8 +219,55 @@ export default class File {
     }
     stack = beforePlugins.concat(stack, afterPlugins);
 
-    // register
-    this.transformerStack = stack.concat(secondaryStack);
+    // build transformer stack
+    this.uncollapsedTransformerStack = stack = stack.concat(secondaryStack);
+
+    // build dependency graph
+    for (var pass of (stack: Array)) {
+      for (var dep of (pass.transformer.dependencies: Array)) {
+        this.transformerDependencies[dep] = pass.key;
+      }
+    }
+
+    // collapse stack categories
+    this.transformerStack = this.collapseStack(stack);
+  }
+
+  collapseStack(_stack) {
+    var stack  = [];
+    var ignore = [];
+
+    for (let pass of (_stack: Array)) {
+      // been merged
+      if (ignore.indexOf(pass) >= 0) continue;
+
+      var group = pass.transformer.metadata.group;
+
+      // can't merge
+      if (!pass.canTransform() || !group) {
+        stack.push(pass);
+        continue;
+      }
+
+      var mergeStack = [];
+      for (let pass of (_stack: Array)) {
+        if (pass.transformer.metadata.group === group) {
+          mergeStack.push(pass);
+          ignore.push(pass);
+        }
+      }
+
+      var visitors = [];
+      for (let pass of (mergeStack: Array)) {
+        visitors.push(pass.handlers);
+      }
+      var visitor = traverse.visitors.merge(visitors);
+      var mergeTransformer = new Transformer(group, visitor);
+      //console.log(mergeTransformer);
+      stack.push(mergeTransformer.buildPass(this));
+    }
+
+    return stack;
   }
 
   set(key: string, val): any {
@@ -337,6 +370,7 @@ export default class File {
       ref._generated = true;
       ref.id = uid;
       ref.type = "FunctionDeclaration";
+      this.attachAuxiliaryComment(ref);
       this.path.unshiftContainer("body", ref);
     } else {
       ref._compact = true;
@@ -357,23 +391,6 @@ export default class File {
     return err;
   }
 
-  checkPath(path) {
-    if (Array.isArray(path)) {
-      for (var i = 0; i < path.length; i++) {
-        this.checkPath(path[i]);
-      }
-      return;
-    }
-
-    var stack = this.transformerStack;
-
-    checkPath(stack, path);
-
-    path.traverse(checkTransformerVisitor, {
-      stack: stack
-    });
-  }
-
   mergeSourceMap(map: Object) {
     var opts = this.opts;
 
@@ -461,10 +478,6 @@ export default class File {
     this._addAst(ast);
     this.log.debug("End set AST");
 
-    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()) {
@@ -473,9 +486,9 @@ export default class File {
     this.log.debug("End module formatter init");
 
     this.call("pre");
-    each(this.transformerStack, function (pass) {
+    for (var pass of (this.transformerStack: Array)) {
       pass.transform();
-    });
+    }
     this.call("post");
   }
 
@@ -540,10 +553,8 @@ export default class File {
   }
 
   call(key: string) {
-    var stack = this.transformerStack;
-    for (var i = 0; i < stack.length; i++) {
-      var transformer = stack[i].transformer;
-      var fn = transformer[key];
+    for (var pass of (this.uncollapsedTransformerStack: Array)) {
+      var fn = pass.transformer[key];
       if (fn) fn(this);
     }
   }

src/babel/transformation/file/logger.js

@@ -1,4 +1,7 @@
-import * as util from  "../../util";
+import buildDebug from "debug/node";
+
+var verboseDebug = buildDebug("babel:verbose");
+var generalDebug = buildDebug("babel");
 
 export default class Logger {
   constructor(file: File, filename: string) {
@@ -22,11 +25,15 @@ export default class Logger {
     }
   }
 
+  verbose(msg: string) {
+    if (verboseDebug.enabled) verboseDebug(this._buildMessage(msg));
+  }
+
   debug(msg: string) {
-    util.debug(this._buildMessage(msg));
+    if (generalDebug.enabled) generalDebug(this._buildMessage(msg));
   }
 
   deopt(node: Object, msg: string) {
-    util.debug(this._buildMessage(msg));
+    this.debug(msg);
   }
 }

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

@@ -68,7 +68,7 @@ export default class PluginManager {
 
     if (name) {
       if (typeof name === "object" && name.transformer) {
-        ({ plugin: name, position } = name);
+        ({ transformer: plugin, 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

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

@@ -1,7 +1,9 @@
 import explode from "./explode-assignable-expression";
 import * as t from "../../types";
 
-export default function (exports, opts) {
+export default function (opts) {
+  var exports = {};
+
   var isAssignment = function (node) {
     return node.operator === opts.operator + "=";
   };
@@ -10,10 +12,6 @@ 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 (this.isCompletionRecord()) return;
@@ -44,4 +42,6 @@ export default function (exports, opts) {
     if (node.operator !== opts.operator) return;
     return opts.build(node.left, node.right);
   };
+
+  return exports;
 };

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

@@ -10,12 +10,6 @@ import * as react from "./react";
 import * as t from "../../types";
 
 export default function (exports, opts) {
-  exports.shouldVisit = function (node) {
-    if (t.isJSX(node)) return true;
-    if (react.isCreateClass(node)) return true;
-    return false;
-  };
-
   exports.JSXIdentifier = function (node, parent) {
     if (node.name === "this" && this.isReferenced()) {
       return t.thisExpression();

src/babel/transformation/index.js

@@ -5,6 +5,13 @@ var pipeline = new Pipeline;
 //
 
 import transformers from "./transformers";
+
+for (var key in transformers) {
+  var transformer = transformers[key];
+  var metadata = transformer.metadata = transformer.metadata || {};
+  metadata.group = metadata.group || "builtin-basic";
+}
+
 pipeline.addTransformers(transformers);
 
 //

src/babel/transformation/modules/_default.js

@@ -5,19 +5,23 @@ import object from "../../helpers/object";
 import * as util from  "../../util";
 import * as t from "../../types";
 
-var remapVisitor = traverse.explode({
+var remapVisitor = {
   enter(node, parent, scope, formatter) {
     if (node._skipModulesRemap) {
       return this.skip();
     }
   },
 
-  Identifier(node, parent, scope, formatter) {
+  ReferencedIdentifier(node, parent, scope, formatter) {
     var remap = formatter.internalRemap[node.name];
 
-    if (this.isReferencedIdentifier() && remap && node !== remap) {
+    if (remap && node !== remap) {
       if (!scope.hasBinding(node.name) || scope.bindingIdentifierEquals(node.name, formatter.localImports[node.name])) {
-        return remap;
+        if (this.key === "callee" && this.parentPath.isCallExpression()) {
+          return t.sequenceExpression([t.literal(0), remap]);
+        } else {
+          return remap;
+        }
       }
     }
   },
@@ -63,7 +67,7 @@ var remapVisitor = traverse.explode({
 
     return t.sequenceExpression(nodes);
   }
-});
+};
 
 var importsVisitor = {
   ImportDeclaration: {
@@ -74,7 +78,7 @@ var importsVisitor = {
   }
 };
 
-var exportsVisitor = traverse.explode({
+var exportsVisitor = {
   ExportDeclaration: {
     enter(node, parent, scope, formatter) {
       formatter.hasLocalExports = true;
@@ -106,7 +110,7 @@ var exportsVisitor = traverse.explode({
       }
     }
   }
-});
+};
 
 export default class DefaultFormatter {
   constructor(file) {

src/babel/transformation/modules/system.js

@@ -1,5 +1,6 @@
 import DefaultFormatter from "./_default";
 import AMDFormatter from "./amd";
+import object from  "../../helpers/object";
 import * as util from  "../../util";
 import last from "lodash/array/last";
 import each from "lodash/collection/each";
@@ -60,12 +61,12 @@ var runnerSettersVisitor = {
   enter(node, parent, scope, state) {
     if (node._importSource === state.source) {
       if (t.isVariableDeclaration(node)) {
-        each(node.declarations, function (declar) {
+        for (var declar of (node.declarations: Array)) {
           state.hoistDeclarators.push(t.variableDeclarator(declar.id));
           state.nodes.push(t.expressionStatement(
             t.assignmentExpression("=", declar.id, declar.init)
           ));
-        });
+        }
       } else {
         state.nodes.push(node);
       }
@@ -143,7 +144,7 @@ export default class SystemFormatter extends AMDFormatter {
       ]));
     }
 
-    this.internalRemap = {};
+    this.internalRemap = object();
 
     this._addImportSource(last(nodes), node);
   }

src/babel/transformation/templates/helper-ludicrous-in.js

@@ -1 +0,0 @@
-Object(RIGHT)[LEFT] !== undefined;

src/babel/transformation/templates/helper-ludicrous-proxy-create.js

@@ -1,4 +0,0 @@
-(function (proxy, directory) {
-  directory.push(proxy);
-  return proxy;
-})

src/babel/transformation/templates/helper-ludicrous-proxy-directory.js

@@ -1 +0,0 @@
-[];

src/babel/transformation/transformer-pass.js

@@ -8,34 +8,26 @@ import traverse from "../traversal";
 
 export default class TransformerPass {
   constructor(file: File, transformer: Transformer) {
-    this.shouldTransform = !transformer.shouldVisit;
-    this.transformer     = transformer;
-    this.handlers        = transformer.handlers;
-    this.skipKey         = transformer.skipKey;
-    this.file            = file;
-    this.ran             = false;
+    this.transformer = transformer;
+    this.handlers    = transformer.handlers;
+    this.file        = file;
+    this.ran         = false;
+    this.key         = transformer.key;
   }
 
   canTransform(): boolean {
-    return this.file.pipeline.canTransform(this.transformer, this.file.opts);
-  }
-
-  checkPath(path: TraversalPath): boolean {
-    if (this.shouldTransform || this.ran) return;
-
-    this.shouldTransform = this.transformer.shouldVisit(path.node);
+    return this.file.transformerDependencies[this.key] ||
+           this.file.pipeline.canTransform(this.transformer, this.file.opts);
   }
 
   transform() {
-    if (!this.shouldTransform) return;
-
     var file = this.file;
 
-    file.log.debug(`Start transformer ${this.transformer.key}`);
+    file.log.debug(`Start transformer ${this.key}`);
 
     traverse(file.ast, this.handlers, file.scope, file);
 
-    file.log.debug(`Finish transformer ${this.transformer.key}`);
+    file.log.debug(`Finish transformer ${this.key}`);
 
     this.ran = true;
   }

src/babel/transformation/transformer.js

@@ -25,8 +25,8 @@ export default class Transformer {
     };
 
     this.manipulateOptions = take("manipulateOptions");
-    this.shouldVisit       = take("shouldVisit");
     this.metadata          = take("metadata") || {};
+    this.dependencies      = this.metadata.dependencies || [];
     this.parser            = take("parser");
     this.post              = take("post");
     this.pre               = take("pre");
@@ -41,18 +41,6 @@ export default class Transformer {
 
     this.handlers = this.normalize(transformer);
     this.key      = transformerKey;
-
-    //
-
-    if (!this.shouldVisit && !this.handlers.enter && !this.handlers.exit) {
-      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 {

src/babel/transformation/transformers/deprecated.json

@@ -5,7 +5,8 @@
   "es6.symbols": "es6.spec.symbols",
   "es6.blockScopingTDZ": "es6.spec.blockScoping",
 
+  "utility.inlineExpressions": "minification.inlineExpressions",
   "utility.deadCodeElimination": "minification.deadCodeElimination",
-  "minification.removeConsoleCalls": "utility.removeConsole",
-  "minification.removeDebugger": "utility.removeDebugger"
+  "utility.removeConsoleCalls": "minification.removeConsole",
+  "utility.removeDebugger": "minification.removeDebugger"
 }

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

@@ -1,10 +1,16 @@
 import * as t from "../../../types";
 
-export function MemberExpression(node) {
-  var prop = node.property;
-  if (!node.computed && t.isIdentifier(prop) && !t.isValidIdentifier(prop.name)) {
-    // foo.default -> foo["default"]
-    node.property = t.literal(prop.name);
-    node.computed = true;
+export var metadata = {
+  group: "builtin-trailing"
+};
+
+export var MemberExpression = {
+  exit(node) {
+    var prop = node.property;
+    if (!node.computed && t.isIdentifier(prop) && !t.isValidIdentifier(prop.name)) {
+      // foo.default -> foo["default"]
+      node.property = t.literal(prop.name);
+      node.computed = true;
+    }
   }
-}
+};

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

@@ -1,9 +1,15 @@
 import * as t from "../../../types";
 
-export function Property(node) {
-  var key = node.key;
-  if (!node.computed && t.isIdentifier(key) && !t.isValidIdentifier(key.name)) {
-    // default: "bar" -> "default": "bar"
-    node.key = t.literal(key.name);
+export var metadata = {
+  group: "builtin-trailing"
+};
+
+export var Property = {
+  exit(node) {
+    var key = node.key;
+    if (!node.computed && t.isIdentifier(key) && !t.isValidIdentifier(key.name)) {
+      // default: "bar" -> "default": "bar"
+      node.key = t.literal(key.name);
+    }
   }
-}
+};

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

@@ -1,10 +1,6 @@
 import * as defineMap from "../../helpers/define-map";
 import * as t from "../../../types";
 
-export function shouldVisit(node) {
-  return t.isProperty(node) && (node.kind === "get" || node.kind === "set");
-}
-
 export function ObjectExpression(node, parent, scope, file) {
   var mutatorMap = {};
   var hasAny = false;

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

@@ -1,7 +1,5 @@
 import * as t from "../../../types";
 
-export var shouldVisit = t.isArrowFunctionExpression;
-
 export function ArrowFunctionExpression(node) {
   t.ensureBlock(node);
 

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

@@ -32,14 +32,14 @@ function isVar(node, parent) {
 }
 
 function standardizeLets(declars) {
-  for (var i = 0; i < declars.length; i++) {
-    delete declars[i]._let;
+  for (var declar of (declars: Array)) {
+    delete declar._let;
   }
 }
 
-export function shouldVisit(node) {
-  return t.isVariableDeclaration(node) && (node.kind === "let" || node.kind === "const");
-}
+export var metadata = {
+  group: "builtin-advanced"
+};
 
 export function VariableDeclaration(node, parent, scope, file) {
   if (!isLet(node, parent)) return;
@@ -109,19 +109,14 @@ function traverseReplace(node, parent, scope, remaps) {
 }
 
 var letReferenceBlockVisitor = {
-  enter(node, parent, scope, state) {
-    if (this.isFunction()) {
-      this.traverse(letReferenceFunctionVisitor, state);
-      return this.skip();
-    }
+  Function(node, parent, scope, state) {
+    this.traverse(letReferenceFunctionVisitor, state);
+    return this.skip();
   }
 };
 
 var letReferenceFunctionVisitor = {
-  enter(node, parent, scope, state) {
-    // not a direct reference
-    if (!this.isReferencedIdentifier()) return;
-
+  ReferencedIdentifier(node, parent, scope, state) {
     var ref = state.letReferences[node.name];
 
     // not a part of our scope
@@ -159,10 +154,8 @@ var hoistVarDeclarationsVisitor = {
 };
 
 var loopLabelVisitor = {
-  enter(node, parent, scope, state) {
-    if (this.isLabeledStatement()) {
-      state.innerLabels.push(node.label.name);
-    }
+  LabeledStatement(node, parent, scope, state) {
+    state.innerLabels.push(node.label.name);
   }
 };
 
@@ -187,19 +180,28 @@ var loopNodeTo = function (node) {
 };
 
 var loopVisitor = {
+  Loop(node, parent, scope, state) {
+    var oldIgnoreLabeless = state.ignoreLabeless;
+    state.ignoreLabeless = true;
+    this.traverse(loopVisitor, state);
+    state.ignoreLabeless = oldIgnoreLabeless;
+    this.skip();
+  },
+
+  Function() {
+    this.skip();
+  },
+
+  SwitchCase(node, parent, scope, state) {
+    var oldInSwitchCase = state.inSwitchCase;
+    state.inSwitchCase = true;
+    this.traverse(loopVisitor, state);
+    state.inSwitchCase = oldInSwitchCase;
+    this.skip();
+  },
+
   enter(node, parent, scope, state) {
     var replace;
-
-    if (this.isLoop()) {
-      state.ignoreLabeless = true;
-      this.traverse(loopVisitor, state);
-      state.ignoreLabeless = false;
-    }
-
-    if (this.isFunction() || this.isLoop()) {
-      return this.skip();
-    }
-
     var loopText = loopNodeTo(node);
 
     if (loopText) {
@@ -215,6 +217,9 @@ var loopVisitor = {
         // they don't refer to the actual loop we're scopifying
         if (state.ignoreLabeless) return;
 
+        //
+        if (state.inSwitchCase) return;
+
         // break statements mean something different in this context
         if (t.isBreakStatement(node) && t.isSwitchCase(parent)) return;
       }
@@ -233,6 +238,7 @@ var loopVisitor = {
 
     if (replace) {
       replace = t.returnStatement(replace);
+      this.skip();
       return t.inherits(replace, node);
     }
   }
@@ -467,18 +473,17 @@ class BlockScoping {
     var block = this.block;
 
     var declarators = block._letDeclarators || [];
-    var declar;
 
     //
     for (let i = 0; i < declarators.length; i++) {
-      declar = declarators[i];
+      let declar = declarators[i];
       extend(this.outsideLetReferences, t.getBindingIdentifiers(declar));
     }
 
     //
     if (block.body) {
       for (let i = 0; i < block.body.length; i++) {
-        declar = block.body[i];
+        let declar = block.body[i];
         if (isLet(declar, block)) {
           declarators = declarators.concat(declar.declarations);
         }
@@ -487,7 +492,7 @@ class BlockScoping {
 
     //
     for (let i = 0; i < declarators.length; i++) {
-      declar = declarators[i];
+      let declar = declarators[i];
       var keys = t.getBindingIdentifiers(declar);
       extend(this.letReferences, keys);
       this.hasLetReferences = true;
@@ -524,6 +529,7 @@ class BlockScoping {
     var state = {
       hasBreakContinue: false,
       ignoreLabeless:   false,
+      inSwitchCase:     false,
       innerLabels:      [],
       hasReturn:        false,
       isLoop:           !!this.loop,

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

@@ -11,8 +11,6 @@ import * as t from "../../../types";
 
 const PROPERTY_COLLISION_METHOD_NAME = "__initializeProperties";
 
-export var shouldVisit = t.isClass;
-
 export function ClassDeclaration(node, parent, scope, file) {
   return t.variableDeclaration("let", [
     t.variableDeclarator(node.id, t.toExpression(node))
@@ -37,7 +35,7 @@ var collectPropertyReferencesVisitor = {
   }
 };
 
-var constructorVisitor = traverse.explode({
+var constructorVisitor = {
   ThisExpression: {
     enter(node, parent, scope, ref) {
       return ref;
@@ -51,9 +49,9 @@ var constructorVisitor = traverse.explode({
       }
     }
   }
-});
+};
 
-var verifyConstructorVisitor = traverse.explode({
+var verifyConstructorVisitor = {
   MethodDefinition: {
     enter() {
       this.skip();
@@ -98,7 +96,7 @@ var verifyConstructorVisitor = traverse.explode({
       }
     }
   }
-});
+};
 
 class ClassTransformer {
 
@@ -481,7 +479,7 @@ class ClassTransformer {
     if (node.kind === "method") {
       nameMethod.property(node, this.file, path ? path.get("value").scope : this.scope);
 
-      if (this.isLoose) {
+      if (this.isLoose && !node.decorators) {
         // use assignments instead of define properties for loose classes
 
         var classRef = this.classRef;

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

@@ -1,48 +1,31 @@
 import * as messages from "../../../messages";
 import * as t from "../../../types";
 
-export function shouldVisit(node) {
-  return t.isVariableDeclaration(node, { kind: "const" }) || t.isImportDeclaration(node);
-}
+export function AssignmentExpression(node, parent, scope, file) {
+  var ids = this.getBindingIdentifiers();
 
-var visitor = {
-  enter(node, parent, scope, state) {
-    if (this.isAssignmentExpression() || this.isUpdateExpression()) {
-      var ids = this.getBindingIdentifiers();
+  for (var name in ids) {
+    var id = ids[name];
 
-      for (var name in ids) {
-        var id = ids[name];
+    var binding = scope.getBinding(name);
 
-        var constant = state.constants[name];
+    // no binding exists
+    if (!binding) continue;
 
-        // no constant exists
-        if (!constant) continue;
+    // not a constant
+    if (binding.kind !== "const" && binding.kind !== "module") continue;
 
-        var constantIdentifier = constant.identifier;
+    // check if the assignment id matches the constant declaration id
+    // if it does then it was the id used to initially declare the
+    // constant so we can just ignore it
+    if (binding.identifier === id) continue;
 
-        // check if the assignment id matches the constant declaration id
-        // if it does then it was the id used to initially declare the
-        // constant so we can just ignore it
-        if (id === constantIdentifier) continue;
-
-        // check if there's been a local binding that shadows this constant
-        if (!scope.bindingIdentifierEquals(name, constantIdentifier)) continue;
-
-        throw state.file.errorWithNode(id, messages.get("readOnly", name));
-      }
-    } else if (this.isScope()) {
-      this.skip();
-    }
+    throw file.errorWithNode(id, messages.get("readOnly", name));
   }
-};
-
-export function Scopable(node, parent, scope, file) {
-  this.traverse(visitor, {
-    constants: scope.getAllBindingsOfKind("const", "module"),
-    file:      file
-  });
 }
 
+export { AssignmentExpression as UpdateExpression };
+
 export function VariableDeclaration(node) {
   if (node.kind === "const") node.kind = "let";
 }

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

@@ -1,7 +1,9 @@
 import * as messages from "../../../messages";
 import * as t from "../../../types";
 
-export var shouldVisit = t.isPattern;
+export var metadata = {
+  group: "builtin-advanced"
+};
 
 export function ForOfStatement(node, parent, scope, file) {
   var left = node.left;
@@ -53,7 +55,7 @@ export function ForOfStatement(node, parent, scope, file) {
 
 export { ForOfStatement as ForInStatement };
 
-exports.Function = function (node, parent, scope, file) {
+export function Func(node, parent, scope, file) {
   var nodes = [];
 
   var hasDestructuring = false;
@@ -83,8 +85,7 @@ exports.Function = function (node, parent, scope, file) {
 
   var block = node.body;
   block.body = nodes.concat(block.body);
-  this.checkSelf();
-};
+}
 
 export function CatchClause(node, parent, scope, file) {
   var pattern = node.param;
@@ -104,8 +105,6 @@ export function CatchClause(node, parent, scope, file) {
   destructuring.init(pattern, ref);
 
   node.body.body = nodes.concat(node.body.body);
-
-  this.checkSelf();
 }
 
 export function ExpressionStatement(node, parent, scope, file) {

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

@@ -2,8 +2,6 @@ import * as messages from "../../../messages";
 import * as util from  "../../../util";
 import * as t from "../../../types";
 
-export var shouldVisit = t.isForOfStatement;
-
 export function ForOfStatement(node, parent, scope, file) {
   if (this.get("right").isArrayExpression()) {
     return _ForOfStatementArray.call(this, node, scope, file);

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

@@ -1,7 +1,5 @@
 import * as t from "../../../types";
 
-export { shouldVisit } from "../internal/modules";
-
 function keepBlockHoist(node, nodes) {
   if (node._blockHoist) {
     for (let i = 0; i < nodes.length; i++) {
@@ -10,6 +8,10 @@ function keepBlockHoist(node, nodes) {
   }
 }
 
+export var metadata = {
+  group: "builtin-modules"
+};
+
 export function ImportDeclaration(node, parent, scope, file) {
   // flow type
   if (node.isType) return;

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

@@ -1,33 +1,20 @@
 import ReplaceSupers from "../../helpers/replace-supers";
 import * as t from "../../../types";
 
-export var shouldVisit = t.isSuper;
-
 function Property(path, node, scope, getObjectRef, file) {
-  if (!node.method) return;
-
-  var value = node.value;
-  var thisExpr = scope.generateUidIdentifier("this");
+  if (!node.method && node.kind === "init") return;
+  if (!t.isFunction(node.value)) return;
 
   var replaceSupers = new ReplaceSupers({
-    topLevelThisReference: thisExpr,
-    getObjectRef:          getObjectRef,
-    methodNode:            node,
-    methodPath:            path,
-    isStatic:              true,
-    scope:                 scope,
-    file:                  file
+    getObjectRef: getObjectRef,
+    methodNode:   node,
+    methodPath:   path,
+    isStatic:     true,
+    scope:        scope,
+    file:         file
   });
 
   replaceSupers.replace();
-
-  if (replaceSupers.hasSuper) {
-    value.body.body.unshift(
-      t.variableDeclaration("var", [
-        t.variableDeclarator(thisExpr, t.thisExpression())
-      ])
-    );
-  }
 }
 
 export function ObjectExpression(node, parent, scope, file) {

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

@@ -3,10 +3,6 @@ import * as util from  "../../../util";
 import traverse from  "../../../traversal";
 import * as t from "../../../types";
 
-export function shouldVisit(node) {
-  return t.isFunction(node) && hasDefaults(node);
-}
-
 var hasDefaults = function (node) {
   for (var i = 0; i < node.params.length; i++) {
     if (!t.isIdentifier(node.params[i])) return true;
@@ -14,17 +10,19 @@ var hasDefaults = function (node) {
   return false;
 };
 
-var iifeVisitor = traverse.explode({
+var iifeVisitor = {
   ReferencedIdentifier(node, parent, scope, state) {
-    if (!state.scope.hasOwnBinding(node.name)) return;
-    if (state.scope.bindingIdentifierEquals(node.name, node)) return;
+    if (node.name !== "eval") {
+      if (!state.scope.hasOwnBinding(node.name)) return;
+      if (state.scope.bindingIdentifierEquals(node.name, node)) return;
+    }
 
     state.iife = true;
     this.stop();
   }
-});
+};
 
-exports.Function = function (node, parent, scope, file) {
+export function Func(node, parent, scope, file) {
   if (!hasDefaults(node)) return;
 
   t.ensureBlock(node);
@@ -96,6 +94,4 @@ exports.Function = function (node, parent, scope, file) {
   } else {
     node.body.body = body.concat(node.body.body);
   }
-
-  this.checkSelf();
-};
+}

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

@@ -2,8 +2,6 @@ import isNumber from "lodash/lang/isNumber";
 import * as util from  "../../../util";
 import * as t from "../../../types";
 
-export var shouldVisit = t.isRestElement;
-
 var memberExpressionOptimisationVisitor = {
   enter(node, parent, scope, state) {
     // check if this scope has a local binding that will shadow the rest parameter
@@ -55,7 +53,7 @@ var hasRest = function (node) {
   return t.isRestElement(node.params[node.params.length - 1]);
 };
 
-exports.Function = function (node, parent, scope, file) {
+export function Func(node, parent, scope, file) {
   if (!hasRest(node)) return;
 
   var rest = node.params.pop().argument;
@@ -96,7 +94,6 @@ exports.Function = function (node, parent, scope, file) {
       candidate.replaceWith(argsId);
       optimizeMemberExpression(candidate.parent, node.params.length);
     }
-    this.checkSelf();
     return;
   }
 
@@ -138,5 +135,4 @@ exports.Function = function (node, parent, scope, file) {
   });
   loop._blockHoist = node.params.length + 1;
   node.body.body.unshift(loop);
-  this.checkSelf();
-};
+}

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

@@ -63,42 +63,40 @@ function spec(node, body, objId, initProps, file) {
   }
 }
 
-export function shouldVisit(node) {
-  return t.isProperty(node) && node.computed;
-}
+export var ObjectExpression = {
+  exit(node, parent, scope, file) {
+    var hasComputed = false;
 
-export function ObjectExpression(node, parent, scope, file) {
-  var hasComputed = false;
+    for (var prop of (node.properties: Array)) {
+      hasComputed = t.isProperty(prop, { computed: true, kind: "init" });
+      if (hasComputed) break;
+    }
 
-  for (var i = 0; i < node.properties.length; i++) {
-    hasComputed = t.isProperty(node.properties[i], { computed: true, kind: "init" });
-    if (hasComputed) break;
+    if (!hasComputed) return;
+
+    var initProps = [];
+    var objId = scope.generateUidBasedOnNode(parent);
+
+    //
+
+    var body = [];
+
+    //
+
+    var callback = spec;
+    if (file.isLoose("es6.properties.computed")) callback = loose;
+
+    var result = callback(node, body, objId, initProps, file);
+    if (result) return result;
+
+    //
+
+    body.unshift(t.variableDeclaration("var", [
+      t.variableDeclarator(objId, t.objectExpression(initProps))
+    ]));
+
+    body.push(t.expressionStatement(objId));
+
+    return body;
   }
-
-  if (!hasComputed) return;
-
-  var initProps = [];
-  var objId = scope.generateUidBasedOnNode(parent);
-
-  //
-
-  var body = [];
-
-  //
-
-  var callback = spec;
-  if (file.isLoose("es6.properties.computed")) callback = loose;
-
-  var result = callback(node, body, objId, initProps, file);
-  if (result) return result;
-
-  //
-
-  body.unshift(t.variableDeclaration("var", [
-    t.variableDeclarator(objId, t.objectExpression(initProps))
-  ]));
-
-  body.push(t.expressionStatement(objId));
-
-  return body;
-}
+};

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

@@ -1,9 +1,3 @@
-import * as t from "../../../types";
-
-export function shouldVisit(node) {
-  return t.isProperty(node) && (node.method || node.shorthand);
-}
-
 export function Property(node) {
   if (node.method) {
     node.method = false;
@@ -11,6 +5,5 @@ export function Property(node) {
 
   if (node.shorthand) {
     node.shorthand = false;
-    node.key = t.removeComments(t.clone(node.key));
   }
 }

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

@@ -1,10 +1,6 @@
 import * as regex from "../../helpers/regex";
 import * as t from "../../../types";
 
-export function shouldVisit(node) {
-  return regex.is(node, "y");
-}
-
 export function Literal(node) {
   if (!regex.is(node, "y")) return;
   return t.newExpression(t.identifier("RegExp"), [

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

@@ -1,10 +1,6 @@
 import rewritePattern from "regexpu/rewrite-pattern";
 import * as regex from "../../helpers/regex";
 
-export function shouldVisit(node) {
-  return regex.is(node, "u");
-}
-
 export function Literal(node) {
   if (!regex.is(node, "u")) return;
   node.regex.pattern = rewritePattern(node.regex.pattern, node.regex.flags);

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

@@ -1,7 +1,7 @@
 import traverse from "../../../traversal";
 import * as t from "../../../types";
 
-var visitor = traverse.explode({
+var visitor = {
   ReferencedIdentifier(node, parent, scope, state) {
     if (t.isFor(parent) && parent.left === node) return;
 
@@ -25,20 +25,23 @@ var visitor = traverse.explode({
       return t.logicalExpression("&&", assert, node);
     }
   }
-});
-
-export var metadata = {
-  optional: true
 };
 
-export function BlockStatement(node, parent, scope, file) {
-  var letRefs = node._letReferences;
-  if (!letRefs) return;
+export var metadata = {
+  optional: true,
+  group: "builtin-advanced"
+};
 
-  this.traverse(visitor, {
-    letRefs: letRefs,
-    file:    file
-  });
-}
+export var BlockStatement = {
+  exit(node, parent, scope, file) {
+    var letRefs = node._letReferences;
+    if (!letRefs) return;
+
+    this.traverse(visitor, {
+      letRefs: letRefs,
+      file:    file
+    });
+  }
+};
 
 export { BlockStatement as Program, BlockStatement as Loop };

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

@@ -44,8 +44,6 @@ function build(props, scope) {
   return nodes;
 }
 
-export var shouldVisit = t.isSpreadElement;
-
 export function ArrayExpression(node, parent, scope) {
   var elements = node.elements;
   if (!hasSpread(elements)) return;

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

@@ -6,18 +6,21 @@ import * as util from  "../../../util";
 import map from "lodash/collection/map";
 import * as t from "../../../types";
 
-exports.Function = function (node, parent, scope, file) {
+export var metadata = {
+  group: "builtin-trailing"
+};
+
+export function Func(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)]);
 }
 
-// looks for and replaces tail recursion calls
-var firstPass = traverse.explode({
+var visitor = {
   enter(node, parent, scope, state) {
     if (t.isTryStatement(parent)) {
       if (node === parent.block) {
@@ -29,7 +32,6 @@ var firstPass = traverse.explode({
   },
 
   ReturnStatement(node, parent, scope, state) {
-    this.skip();
     return state.subTransform(node.argument);
   },
 
@@ -38,61 +40,35 @@ var firstPass = traverse.explode({
   },
 
   VariableDeclaration(node, parent, scope, state) {
-    this.skip();
     state.vars.push(node);
-  }
-});
+  },
 
-// hoists up function declarations, replaces `this` and `arguments` and marks
-// them as needed
-var secondPass = traverse.explode({
   ThisExpression(node, parent, scope, state) {
     state.needsThis = true;
-    return state.getThisId();
+    state.thisPaths.push(this);
   },
 
   ReferencedIdentifier(node, parent, scope, state) {
-    if (node.name !== "arguments") return;
-    state.needsArguments = true;
-    return state.getArgumentsId();
-  },
-
-  Function(node, parent, scope, state) {
-    this.skip();
-    if (this.isFunctionDeclaration()) {
-      node = t.variableDeclaration("var", [
-        t.variableDeclarator(node.id, t.toExpression(node))
-      ]);
-      node._blockHoist = 2;
-      return node;
+    if (node.name === "arguments") {
+      state.needsArguments = true;
+      state.argumentsPaths.push(this);
     }
   }
-});
-
-// optimizes recursion by removing `this` and `arguments` if they aren't used
-var thirdPass = traverse.explode({
-  ExpressionStatement(node, parent, scope, state) {
-    var expr = node.expression;
-    if (!t.isAssignmentExpression(expr)) return;
-
-    if (!state.needsThis && expr.left === state.getThisId()) {
-      this.remove();
-    } else if (!state.needsArguments && expr.left === state.getArgumentsId() && t.isArrayExpression(expr.right)) {
-      return map(expr.right.elements, function (elem) {
-        return t.expressionStatement(elem);
-      });
-    }
-  }
-});
+};
 
 class TailCallTransformer {
   constructor(path, scope, file) {
     this.hasTailRecursion = false;
-    this.needsArguments   = false;
-    this.setsArguments    = false;
-    this.needsThis        = false;
-    this.ownerId          = path.node.id;
-    this.vars             = [];
+
+    this.needsArguments = false;
+    this.argumentsPaths = [];
+    this.setsArguments  = false;
+
+    this.needsThis = false;
+    this.thisPaths = [];
+
+    this.ownerId = path.node.id;
+    this.vars    = [];
 
     this.scope = scope;
     this.path  = path;
@@ -158,10 +134,12 @@ class TailCallTransformer {
     if (!ownerId) return;
 
     // traverse the function and look for tail recursion
-    this.path.traverse(firstPass, this);
+    this.path.traverse(visitor, this);
 
+    // has no tail call recursion
     if (!this.hasTailRecursion) return;
 
+    // the function binding isn't constant so we can't be sure that it's the same function :(
     if (this.hasDeopt()) {
       this.file.log.deopt(node, messages.get("tailCallReassignmentDeopt"));
       return;
@@ -169,21 +147,27 @@ class TailCallTransformer {
 
     //
 
-    this.path.traverse(secondPass, this);
-
-    if (!this.needsThis || !this.needsArguments) {
-      this.path.traverse(thirdPass, this);
-    }
-
     var body = t.ensureBlock(node).body;
 
+    for (var i = 0; i < body.length; i++) {
+      var bodyNode = body[i];
+      if (!t.isFunctionDeclaration(bodyNode)) continue;
+
+      bodyNode = body[i] = t.variableDeclaration("var", [
+        t.variableDeclarator(bodyNode.id, t.toExpression(bodyNode))
+      ]);
+      bodyNode._blockHoist = 2;
+    }
+
     if (this.vars.length > 0) {
       var declarations = flatten(map(this.vars, function (decl) {
         return decl.declarations;
       }));
+
       var assignment = reduceRight(declarations, function (expr, decl) {
         return t.assignmentExpression("=", decl.id, expr);
       }, t.identifier("undefined"));
+
       var statement = t.expressionStatement(assignment);
       statement._blockHoist = Infinity;
       body.unshift(statement);
@@ -191,7 +175,9 @@ class TailCallTransformer {
 
     var paramDecls = this.paramDecls;
     if (paramDecls.length > 0) {
-      body.unshift(t.variableDeclaration("var", paramDecls));
+      var paramDecl = t.variableDeclaration("var", paramDecls);
+      paramDecl._blockHoist = Infinity;
+      body.unshift(paramDecl);
     }
 
     body.unshift(t.expressionStatement(
@@ -199,22 +185,28 @@ class TailCallTransformer {
     );
 
     node.body = util.template("tail-call-body", {
-      AGAIN_ID:      this.getAgainId(),
-      THIS_ID:       this.thisId,
-      ARGUMENTS_ID:  this.argumentsId,
-      FUNCTION_ID:   this.getFunctionId(),
-      BLOCK:         node.body
+      FUNCTION_ID: this.getFunctionId(),
+      AGAIN_ID:    this.getAgainId(),
+      BLOCK:       node.body
     });
 
     var topVars = [];
 
     if (this.needsThis) {
+      for (var path of (this.thisPaths: Array)) {
+        path.replaceWith(this.getThisId());
+      }
+
       topVars.push(t.variableDeclarator(this.getThisId(), t.thisExpression()));
     }
 
     if (this.needsArguments || this.setsArguments) {
-      var decl = t.variableDeclarator(this.getArgumentsId());
-      if (this.needsArguments) {
+      for (var path of (this.argumentsPaths: Array)) {
+        path.replaceWith(this.argumentsId);
+      }
+
+      var decl = t.variableDeclarator(this.argumentsId);
+      if (this.argumentsId) {
         decl.init = t.identifier("arguments");
       }
       topVars.push(decl);
@@ -327,7 +319,7 @@ class TailCallTransformer {
 
     var body = [];
 
-    if (!t.isThisExpression(thisBinding)) {
+    if (this.needsThis && !t.isThisExpression(thisBinding)) {
       body.push(t.expressionStatement(t.assignmentExpression(
         "=",
         this.getThisId(),
@@ -340,29 +332,35 @@ class TailCallTransformer {
     }
 
     var argumentsId = this.getArgumentsId();
-    var params = this.getParams();
+    var params      = this.getParams();
 
-    body.push(t.expressionStatement(t.assignmentExpression(
-      "=",
-      argumentsId,
-      args
-    )));
-
-    var i, param;
+    if (this.needsArguments) {
+      body.push(t.expressionStatement(t.assignmentExpression(
+        "=",
+        argumentsId,
+        args
+      )));
+    }
 
     if (t.isArrayExpression(args)) {
       var elems = args.elements;
-      for (i = 0; i < elems.length && i < params.length; i++) {
-        param = params[i];
+      for (let i = 0; i < elems.length && i < params.length; i++) {
+        let param = params[i];
         var elem = elems[i] || (elems[i] = t.identifier("undefined"));
         if (!param._isDefaultPlaceholder) {
           elems[i] = t.assignmentExpression("=", param, elem);
         }
       }
+
+      if (!this.needsArguments) {
+        for (var elem of (elems: Array)) {
+          body.push(t.expressionStatement(elem));
+        }
+      }
     } else {
       this.setsArguments = true;
-      for (i = 0; i < params.length; i++) {
-        param = params[i];
+      for (let i = 0; i < params.length; i++) {
+        let param = params[i];
         if (!param._isDefaultPlaceholder) {
           body.push(t.expressionStatement(t.assignmentExpression(
             "=",
@@ -376,6 +374,7 @@ class TailCallTransformer {
     body.push(t.expressionStatement(
       t.assignmentExpression("=", this.getAgainId(), t.literal(true))
     ));
+
     body.push(t.continueStatement(this.getFunctionId()));
 
     return body;

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

@@ -4,10 +4,6 @@ var buildBinaryExpression = function (left, right) {
   return t.binaryExpression("+", left, right);
 };
 
-export function shouldVisit(node) {
-  return t.isTemplateLiteral(node) || t.isTaggedTemplateExpression(node);
-}
-
 export function TaggedTemplateExpression(node, parent, scope, file) {
   var quasi = node.quasi;
   var args  = [];

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

@@ -1,7 +1,3 @@
 export var metadata = {
   stage: 1
 };
-
-export function shouldVisit() {
-  return false;
-}

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

@@ -1,7 +1,4 @@
 export var metadata = {
-  stage: 0
+  stage: 0,
+  dependencies: ["es6.classes"]
 };
-
-export function shouldVisit() {
-  return false;
-}

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

@@ -3,14 +3,11 @@ import * as defineMap from "../../helpers/define-map";
 import * as t from "../../../types";
 
 export var metadata = {
+  dependencies: ["es6.classes"],
   optional: true,
   stage: 1
 };
 
-export function shouldVisit(node) {
-  return !!node.decorators;
-}
-
 export function ObjectExpression(node, parent, scope, file) {
   var hasDecorators = false;
   for (var i = 0; i < node.properties.length; i++) {

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

@@ -5,8 +5,6 @@ export var metadata = {
   stage: 0
 };
 
-export var shouldVisit = t.isDoExpression;
-
 export function DoExpression(node) {
   var body = node.body.body;
   if (body.length) {

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

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

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

@@ -6,10 +6,6 @@ export var metadata = {
   stage: 1
 };
 
-export function shouldVisit(node) {
-  return t.isExportDefaultSpecifier(node) || t.isExportNamespaceSpecifier(node);
-}
-
 function build(node, nodes, scope) {
   var first = node.specifiers[0];
   if (!t.isExportNamespaceSpecifier(first) && !t.isExportDefaultSpecifier(first)) return;

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

@@ -3,13 +3,10 @@
 import * as t from "../../../types";
 
 export var metadata = {
-  stage: 1
+  stage: 1,
+  dependencies: ["es6.destructuring"]
 };
 
-export function manipulateOptions(opts) {
-  if (opts.whitelist) opts.whitelist.push("es6.destructuring");
-}
-
 var hasSpread = function (node) {
   for (var i = 0; i < node.properties.length; i++) {
     if (t.isSpreadProperty(node.properties[i])) {

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

@@ -1,7 +1,3 @@
 export var metadata = {
   stage: 1
 };
-
-export function shouldVisit() {
-  return false;
-}

src/babel/transformation/transformers/index.js

@@ -1,124 +1,85 @@
 export default {
-  "utility.removeDebugger":                require("./utility/remove-debugger"),
-  "utility.removeConsole":                 require("./utility/remove-console"),
-
+  //- builtin-setup
+  _explode:                                require("./internal/explode"),
+  _validation:                             require("./internal/validation"),
+  _hoistDirectives:                        require("./internal/hoist-directives"),
+  "minification.removeDebugger":           require("./minification/remove-debugger"),
+  "minification.removeConsole":            require("./minification/remove-console"),
   "utility.inlineEnvironmentVariables":    require("./utility/inline-environment-variables"),
-  "utility.inlineExpressions":             require("./utility/inline-expressions"),
-
+  "minification.inlineExpressions":        require("./minification/inline-expressions"),
   "minification.deadCodeElimination":      require("./minification/dead-code-elimination"),
-
   _modules:                                require("./internal/modules"),
+  "spec.functionName":                     require("./spec/function-name"),
 
+  //- builtin-basic
+  // this is where the bulk of the ES6 transformations take place, none of them require traversal state
+  // so they can all be concatenated together for performance
   "es7.classProperties":                   require("./es7/class-properties"),
   "es7.trailingFunctionCommas":            require("./es7/trailing-function-commas"),
   "es7.asyncFunctions":                    require("./es7/async-functions"),
   "es7.decorators":                        require("./es7/decorators"),
-
   strict:                                  require("./other/strict"),
-
-  _validation:                             require("./internal/validation"),
-
   "validation.undeclaredVariableCheck":    require("./validation/undeclared-variable-check"),
   "validation.react":                      require("./validation/react"),
-
-  // this goes at the start so we only transform the original user code
-  "spec.functionName":                     require("./spec/function-name"),
-
-  // needs to be before `_shadowFunctions`
   "es6.arrowFunctions":                    require("./es6/arrow-functions"),
-
   "spec.blockScopedFunctions":             require("./spec/block-scoped-functions"),
-
   "optimisation.react.constantElements":   require("./optimisation/react.constant-elements"),
   "optimisation.react.inlineElements":     require("./optimisation/react.inline-elements"),
   reactCompat:                             require("./other/react-compat"),
   react:                                   require("./other/react"),
-
-  // needs to be before `regenerator` due to generator comprehensions
-  // needs to be before `_shadowFunctions`
   "es7.comprehensions":                    require("./es7/comprehensions"),
-
   "es6.classes":                           require("./es6/classes"),
-
   asyncToGenerator:                        require("./other/async-to-generator"),
   bluebirdCoroutines:                      require("./other/bluebird-coroutines"),
-
   "es6.objectSuper":                       require("./es6/object-super"),
   "es7.objectRestSpread":                  require("./es7/object-rest-spread"),
   "es7.exponentiationOperator":            require("./es7/exponentiation-operator"),
-
   "es6.spec.templateLiterals":             require("./es6/spec.template-literals"),
   "es6.templateLiterals":                  require("./es6/template-literals"),
-
   "es5.properties.mutators":               require("./es5/properties.mutators"),
   "es6.properties.shorthand":              require("./es6/properties.shorthand"),
-
-  // needs to be before `_shadowFunctions` due to define property closure
   "es6.properties.computed":               require("./es6/properties.computed"),
-
   "optimisation.flow.forOf":               require("./optimisation/flow.for-of"),
   "es6.forOf":                             require("./es6/for-of"),
-
   "es6.regex.sticky":                      require("./es6/regex.sticky"),
   "es6.regex.unicode":                     require("./es6/regex.unicode"),
-
   "es6.constants":                         require("./es6/constants"),
-
-  // needs to be before `es6.parameters.default` as default parameters will destroy the rest param
   "es6.parameters.rest":                   require("./es6/parameters.rest"),
-
-  // needs to be after `es6.parameters.rest` as we use `toArray` and avoid turning an already known array into one
   "es6.spread":                            require("./es6/spread"),
-
-  // needs to be before `es6.blockScoping` as default parameters have a TDZ
   "es6.parameters.default":                require("./es6/parameters.default"),
+  "es7.exportExtensions":                  require("./es7/export-extensions"),
+  "spec.protoToAssign":                    require("./spec/proto-to-assign"),
+  "es7.doExpressions":                     require("./es7/do-expressions"),
+  "es6.spec.symbols":                      require("./es6/spec.symbols"),
+  "spec.undefinedToVoid":                  require("./spec/undefined-to-void"),
+  jscript:                                 require("./other/jscript"),
+  flow:                                    require("./other/flow"),
 
-  // needs to be before `es6.blockScoping` as let variables may be produced
+  //- builtin-advanced
   "es6.destructuring":                     require("./es6/destructuring"),
-
-  // needs to be before `_shadowFunctions` due to block scopes sometimes being wrapped in a
-  // closure
   "es6.blockScoping":                      require("./es6/block-scoping"),
-
-  // needs to be after `es6.blockScoping` due to needing `letReferences` set on blocks
   "es6.spec.blockScoping":                 require("./es6/spec.block-scoping"),
 
-  // needs to be after `es6.parameters.*` and `es6.blockScoping` due to needing pure
-  // identifiers in parameters and variable declarators
-  "es6.tailCall":                          require("./es6/tail-call"),
+  // es6 syntax transformation is **forbidden** past this point since regenerator will chuck a massive
+  // hissy fit
 
+  //- regenerator
   regenerator:                             require("./other/regenerator"),
 
-  // needs to be after `regenerator` due to needing `regeneratorRuntime` references
-  // needs to be after `es6.forOf` due to needing `Symbol.iterator` references
-  // needs to be before `es6.modules` due to dynamic imports
-  runtime:                                require("./other/runtime"),
-
-  // needs to be before `_blockHoist` due to function hoisting etc
-  "es7.exportExtensions":                  require("./es7/export-extensions"),
+  //- builtin-modules
+  runtime:                                 require("./other/runtime"),
   "es6.modules":                           require("./es6/modules"),
-
-  _blockHoist:                             require("./internal/block-hoist"),
-
-  "spec.protoToAssign":                    require("./spec/proto-to-assign"),
-
-  _shadowFunctions:                        require("./internal/shadow-functions"),
-
-  "es7.doExpressions":                     require("./es7/do-expressions"),
-
-  "es6.spec.symbols":                      require("./es6/spec.symbols"),
-  ludicrous:                               require("./other/ludicrous"),
-  "spec.undefinedToVoid":                  require("./spec/undefined-to-void"),
-
-  _strict:                                 require("./internal/strict"),
   _moduleFormatter:                        require("./internal/module-formatter"),
 
+  //- builtin-trailing
+  // these clean up the output and do finishing up transformations, it's important to note that by this
+  // stage you can't import any new modules or insert new ES6 as all those transformers have already
+  // been ran
+  "es6.tailCall":                          require("./es6/tail-call"),
+  _shadowFunctions:                        require("./internal/shadow-functions"),
   "es3.propertyLiterals":                  require("./es3/property-literals"),
   "es3.memberExpressionLiterals":          require("./es3/member-expression-literals"),
-
   "minification.memberExpressionLiterals": require("./minification/member-expression-literals"),
   "minification.propertyLiterals":         require("./minification/property-literals"),
-
-  jscript:                                 require("./other/jscript"),
-  flow:                                    require("./other/flow")
+  _blockHoist:                             require("./internal/block-hoist"),
 };

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

@@ -1,5 +1,9 @@
 import sortBy from "lodash/collection/sortBy";
 
+export var metadata = {
+  group: "builtin-trailing"
+};
+
 // Priority:
 //
 //  - 0 We want this to be at the **very** bottom

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

@@ -0,0 +1,30 @@
+import clone from "lodash/lang/clone";
+import * as t from "../../../types";
+
+export var metadata = {
+  group: "builtin-setup"
+};
+
+function buildClone(bindingKey, refKey) {
+  return function (node) {
+    if (node[bindingKey] === node[refKey]) {
+      node[refKey] = t.removeComments(clone(node[refKey]));
+    }
+  };
+}
+
+function buildListClone(listKey, bindingKey, refKey) {
+  var clone = buildClone(bindingKey, refKey);
+
+  return function (node) {
+    if (!node[listKey]) return;
+
+    for (var subNode of (node[listKey]: Array)) {
+      clone(subNode);
+    }
+  };
+}
+
+export var Property = buildClone("value", "key");
+export var ExportDeclaration = buildListClone("specifiers", "local", "exported");
+export var ImportDeclaration = buildListClone("specifiers", "local", "imported");

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

@@ -0,0 +1,20 @@
+import * as t from "../../../types";
+
+export var metadata = {
+  group: "builtin-setup"
+};
+
+export var BlockStatement = {
+  exit(node) {
+    for (var i = 0; i < node.body.length; i++) {
+      var bodyNode = node.body[i];
+      if (t.isExpressionStatement(bodyNode) && t.isLiteral(bodyNode.expression)) {
+        bodyNode._blockHoist = Infinity;
+      } else {
+        return;
+      }
+    }
+  }
+};
+
+export { BlockStatement as Program };

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

@@ -1,15 +1,24 @@
 import * as strict from "../../helpers/strict";
 
-export function Program(program, parent, scope, file) {
-  this.stop();
+export var metadata = {
+  group: "builtin-modules"
+};
 
-  strict.wrap(program, function () {
-    program.body = file.dynamicImports.concat(program.body);
-  });
+export var Program = {
+  exit(program, parent, scope, file) {
+    strict.wrap(program, function () {
+      // ensure that these are at the top, just like normal imports
+      for (var node of (file.dynamicImports: Array)) {
+        node._blockHoist = 3;
+      }
 
-  if (!file.transformers["es6.modules"].canTransform()) return;
+      program.body = file.dynamicImports.concat(program.body);
+    });
 
-  if (file.moduleFormatter.transform) {
-    file.moduleFormatter.transform(program);
+    if (!file.transformers["es6.modules"].canTransform()) return;
+
+    if (file.moduleFormatter.transform) {
+      file.moduleFormatter.transform(program);
+    }
   }
-}
+};

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

@@ -4,11 +4,12 @@
 // a generator function as a default then regenerator will destroy the export
 // declaration and leave a variable declaration in it's place... yeah, handy.
 
+import clone from "lodash/lang/clone";
 import * as t from "../../../types";
 
-export function shouldVisit(node) {
-  return t.isImportDeclaration(node) || t.isExportDeclaration(node);
-}
+export var metadata = {
+  group: "builtin-setup"
+};
 
 export function ImportDeclaration(node, parent, scope, file) {
   if (node.source) {
@@ -48,6 +49,10 @@ export function ExportDefaultDeclaration(node, parent, scope) {
   }
 }
 
+function buildExportSpecifier(id) {
+  return t.exportSpecifier(clone(id), clone(id));
+}
+
 export function ExportNamedDeclaration(node, parent, scope) {
   ImportDeclaration.apply(this, arguments);
 
@@ -60,12 +65,12 @@ export function ExportNamedDeclaration(node, parent, scope) {
 
   if (t.isClassDeclaration(declar)) {
     // export class Foo {}
-    node.specifiers  = [t.exportSpecifier(declar.id, declar.id)];
+    node.specifiers  = [buildExportSpecifier(declar.id)];
     node.declaration = null;
     return [getDeclar(), node];
   } else if (t.isFunctionDeclaration(declar)) {
     // export function Foo() {}
-    node.specifiers  = [t.exportSpecifier(declar.id, declar.id)];
+    node.specifiers  = [buildExportSpecifier(declar.id)];
     node.declaration = null;
     node._blockHoist = 2;
     return [getDeclar(), node];
@@ -74,8 +79,7 @@ export function ExportNamedDeclaration(node, parent, scope) {
     var specifiers = [];
     var bindings = this.get("declaration").getBindingIdentifiers();
     for (var key in bindings) {
-      var id = bindings[key];
-      specifiers.push(t.exportSpecifier(id, id));
+      specifiers.push(buildExportSpecifier(bindings[key]));
     }
     return [declar, t.exportNamedDeclaration(null, specifiers)];
   }

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

@@ -1,102 +1,33 @@
 import * as t from "../../../types";
 
-var functionChildrenVisitor = {
-  enter(node, parent, scope, state) {
-    if (this.isClass(node)) {
-      return this.skip();
-    }
-
-    if (this.isFunction() && !node.shadow) {
-      return this.skip();
-    }
-
-    if (node._shadowedFunctionLiteral) return this.skip();
-
-    var getId;
-
-    if (this.isIdentifier() && node.name === "arguments") {
-      getId = state.getArgumentsId;
-    } else if (this.isThisExpression()) {
-      getId = state.getThisId;
-    } else {
-      return;
-    }
-
-    if (this.isReferenced()) return getId();
-  }
+export var metadata = {
+  group: "builtin-trailing"
 };
 
-var functionVisitor = {
-  enter(node, parent, scope, state) {
-   if (!node.shadow) {
-      if (this.isFunction()) {
-        // stop traversal of this node as it'll be hit again by this transformer
-        return this.skip();
-      } else {
-        return;
-      }
-    }
+function remap(path, key, create) {
+  // ensure that we're shadowed
+  if (!path.inShadow()) return;
 
-    // traverse all child nodes of this function and find `arguments` and `this`
-    this.traverse(functionChildrenVisitor, state);
+  var fnPath = path.findParent((node, path) => !node.shadow && (path.isFunction() || path.isProgram()));
 
-    node.shadow = false;
+  var cached = fnPath.getData(key);
+  if (cached) return cached;
 
-    return this.skip();
-  }
-};
+  var init = create();
+  var id   = path.scope.generateUidIdentifier(key);
 
-function aliasFunction(getBody, path, scope) {
-  var argumentsId;
-  var thisId;
+  fnPath.setData(key, id);
+  fnPath.scope.push({ id, init });
 
-  var state = {
-    getArgumentsId() {
-      return argumentsId = argumentsId || scope.generateUidIdentifier("arguments");
-    },
-
-    getThisId() {
-      return thisId = thisId || scope.generateUidIdentifier("this");
-    }
-  };
-
-  // traverse the function and find all alias functions so we can alias
-  // `arguments` and `this` if necessary
-  path.traverse(functionVisitor, state);
-
-  var body;
-
-  var pushDeclaration = function (id, init) {
-    body = body || getBody();
-    body.unshift(t.variableDeclaration("var", [
-      t.variableDeclarator(id, init)
-    ]));
-  };
-
-  if (argumentsId) {
-    pushDeclaration(argumentsId, t.identifier("arguments"));
-  }
-
-  if (thisId) {
-    pushDeclaration(thisId, t.thisExpression());
-  }
-};
-
-export function shouldVisit(node) {
-  return true;
+  return id;
 }
 
-export function Program(node, parent, scope) {
-  aliasFunction(function () {
-    return node.body;
-  }, this, scope);
-};
-
-export function FunctionDeclaration(node, parent, scope) {
-  aliasFunction(function () {
-    t.ensureBlock(node);
-    return node.body.body;
-  }, this, scope);
+export function ThisExpression() {
+  return remap(this, "this", () => t.thisExpression());
 }
 
-export { FunctionDeclaration as FunctionExpression };
+export function ReferencedIdentifier(node) {
+  if (node.name === "arguments" && !node._shadowedFunctionLiteral) {
+    return remap(this, "arguments", () => t.identifier("arguments"));
+  }
+}

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

@@ -1,18 +0,0 @@
-import * as t from "../../../types";
-
-export function Program(program, parent, scope, file) {
-  if (file.transformers.strict.canTransform()) {
-    var directive = file.get("existingStrictDirective");
-
-    if (!directive) {
-      directive = t.expressionStatement(t.literal("use strict"));
-      var first = program.body[0];
-      if (first) {
-        directive.leadingComments = first.leadingComments;
-        first.leadingComments = [];
-      }
-    }
-
-    this.unshiftContainer("body", [directive]);
-  }
-}

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

@@ -2,7 +2,7 @@ import * as messages from "../../../messages";
 import * as t from "../../../types";
 
 export var metadata = {
-  readOnly: true
+  group: "builtin-setup"
 };
 
 export function ForOfStatement(node, parent, scope, file) {
@@ -43,16 +43,3 @@ export function Property(node, parent, scope, file) {
     }
   }
 }
-
-export function BlockStatement(node) {
-  for (var i = 0; i < node.body.length; i++) {
-    var bodyNode = node.body[i];
-    if (t.isExpressionStatement(bodyNode) && t.isLiteral(bodyNode.expression)) {
-      bodyNode._blockHoist = Infinity;
-    } else {
-      return;
-    }
-  }
-}
-
-export { BlockStatement as Program };

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

@@ -18,7 +18,8 @@ function toStatements(node) {
 }
 
 export var metadata = {
-  optional: true
+  optional: true,
+  group: "builtin-setup"
 };
 
 export function Identifier(node, parent, scope) {
@@ -26,6 +27,7 @@ export function Identifier(node, parent, scope) {
 
   var binding = scope.getBinding(node.name);
   if (!binding || binding.references > 1 || !binding.constant) return;
+  if (binding.kind === "param") return;
 
   var replacement = binding.path.node;
   if (t.isVariableDeclarator(replacement)) {

src/babel/transformation/transformers/minification/inline-expressions.js

@@ -1,7 +1,8 @@
 import * as t from "../../../types";
 
 export var metadata = {
-  optional: true
+  optional: true,
+  group: "builtin-setup"
 };
 
 export function Expression(node, parent, scope) {

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

@@ -1,14 +1,17 @@
 import * as t from "../../../types";
 
 export var metadata = {
-  optional: true
+  optional: true,
+  group: "builtin-trailing"
 };
 
-export function MemberExpression(node) {
-  var prop = node.property;
-  if (node.computed && t.isLiteral(prop) && t.isValidIdentifier(prop.value)) {
-    // foo["bar"] => foo.bar
-    node.property = t.identifier(prop.value);
-    node.computed = false;
+export var MemberExpression = {
+  exit(node) {
+    var prop = node.property;
+    if (node.computed && t.isLiteral(prop) && t.isValidIdentifier(prop.value)) {
+      // foo["bar"] => foo.bar
+      node.property = t.identifier(prop.value);
+      node.computed = false;
+    }
   }
-}
+};

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

@@ -1,14 +1,17 @@
 import * as t from "../../../types";
 
 export var metadata = {
-  optional: true
+  optional: true,
+  group: "builtin-trailing"
 };
 
-export function Property(node) {
-  var key = node.key;
-  if (t.isLiteral(key) && t.isValidIdentifier(key.value)) {
-    // "foo": "bar" -> foo: "bar"
-    node.key = t.identifier(key.value);
-    node.computed = false;
+export var Property = {
+  exit(node) {
+    var key = node.key;
+    if (t.isLiteral(key) && t.isValidIdentifier(key.value)) {
+      // "foo": "bar" -> foo: "bar"
+      node.key = t.identifier(key.value);
+      node.computed = false;
+    }
   }
-}
+};

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

@@ -1,7 +1,8 @@
 import * as t from "../../../types";
 
 export var metadata = {
-  optional: true
+  optional: true,
+  group: "builtin-setup"
 };
 
 export function CallExpression(node, parent) {

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

@@ -1,7 +1,8 @@
 import * as t from "../../../types";
 
 export var metadata = {
-  optional: true
+  optional: true,
+  group: "builtin-setup"
 };
 
 export function ExpressionStatement(node) {

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

@@ -1,7 +1,6 @@
 import { _ForOfStatementArray } from "../es6/for-of";
 import * as t from "../../../types";
 
-export var shouldVisit = t.isForOfStatement;
 export var metadata = {
   optional: true
 };

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

@@ -3,11 +3,12 @@ import remapAsyncToGenerator from "../../helpers/remap-async-to-generator";
 export { manipulateOptions } from "./bluebird-coroutines";
 
 export var metadata = {
-  optional: true
+  optional: true,
+  dependencies: ["es7.asyncFunctions", "es6.classes"]
 };
 
-exports.Function = function (node, parent, scope, file) {
+export function Func(node, parent, scope, file) {
   if (!node.async || node.generator) return;
 
   return remapAsyncToGenerator(node, file.addHelper("async-to-generator"), scope);
-};
+}

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

@@ -2,15 +2,15 @@ import remapAsyncToGenerator from "../../helpers/remap-async-to-generator";
 import * as t from "../../../types";
 
 export function manipulateOptions(opts) {
-  opts.optional.push("es7.asyncFunctions");
   opts.blacklist.push("regenerator");
 }
 
 export var metadata = {
-  optional: true
+  optional: true,
+  dependencies: ["es7.asyncFunctions", "es6.classes"]
 };
 
-exports.Function = function (node, parent, scope, file) {
+export function Func(node, parent, scope, file) {
   if (!node.async || node.generator) return;
 
   return remapAsyncToGenerator(
@@ -18,4 +18,4 @@ exports.Function = function (node, parent, scope, file) {
     t.memberExpression(file.addImport("bluebird", null, "absolute"), t.identifier("coroutine")),
     scope
   );
-};
+}

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

@@ -1,28 +1,23 @@
 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();
 }
 
 export function ClassProperty(node) {
   node.typeAnnotation = null;
-  if (!node.value) this.remove();
 }
 
 export function Class(node) {
   node.implements = null;
 }
 
-exports.Function = function (node) {
+export function Func(node) {
   for (var i = 0; i < node.params.length; i++) {
     var param = node.params[i];
     param.optional = false;
   }
-};
+}
 
 export function TypeCastExpression(node) {
   return node.expression;

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

@@ -1,66 +0,0 @@
-import * as t from "../../../types";
-import * as util from "../../../util";
-
-export var metadata = {
-  optional: true
-};
-
-// foo in bar
-export function BinaryExpression(node) {
-  if (node.operator === "in") {
-    return util.template("ludicrous-in", {
-      LEFT: node.left,
-      RIGHT: node.right
-    });
-  }
-}
-
-// { 1: "foo" }
-export function Property(node) {
-  var key = node.key;
-  if (t.isLiteral(key) && typeof key.value === "number") {
-    key.value = "" + key.value;
-  }
-}
-
-// /foobar/g
-export function Literal(node) {
-  if (node.regex) {
-    node.regex.pattern = "foobar";
-    node.regex.flags = "";
-  }
-}
-
-// foo.bar
-export function MemberExpression(node) {
-
-}
-
-// Object.setPrototypeOf
-// Object.preventExtensions
-// Object.keys
-// Object.isExtensible
-// Object.getOwnPropertyDescriptor
-// Object.defineProperty
-export function CallExpression(node) {
-
-}
-
-// delete foo.bar
-export function UnaryExpression(node) {
-
-}
-
-// foo.bar = bar;
-export function AssignmentExpression(node) {
-
-}
-
-// new Proxy
-export function NewExpression(node, parent, scope, file) {
-  if (this.get("callee").isIdentifier({ name: "Proxy" })) {
-    return t.callExpression(file.addHelper("proxy-create"), [node.arguments[0], file.addHelper("proxy-directory")]);
-  } else {
-    // possible proxy constructor
-  }
-}

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

@@ -1,14 +1,10 @@
 import regenerator from "regenerator";
 import * as t from "../../../types";
 
-export function shouldVisit(node) {
-  return t.isFunction(node) && (node.async || node.generator);
-}
-
-export var Program = {
-  enter(ast) {
-    regenerator.transform(ast);
-    this.stop();
-    this.checkSelf();
-  }
+export var metadata = {
+  group: "regenerator"
 };
+
+export function Program(ast) {
+  regenerator.transform(ast);
+}

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

@@ -9,98 +9,12 @@ var isSymbolIterator = t.buildMatchMemberExpression("Symbol.iterator");
 
 const RUNTIME_MODULE_NAME = "babel-runtime";
 
-var astVisitor = traverse.explode({
-  Identifier(node, parent, scope, file) {
-    if (!this.isReferenced()) return;
-    if (t.isMemberExpression(parent)) return;
-    if (!has(definitions.builtins, node.name)) return;
-    if (scope.getBindingIdentifier(node.name)) return;
-
-    // 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");
-  },
-
-  CallExpression(node, parent, scope, file) {
-    // arr[Symbol.iterator]() -> _core.$for.getIterator(arr)
-
-    var callee = node.callee;
-    if (node.arguments.length) return;
-
-    if (!t.isMemberExpression(callee)) return;
-    if (!callee.computed) return;
-
-    var prop = callee.property;
-    if (!isSymbolIterator(prop)) return;
-
-    return t.callExpression(file.addImport(`${RUNTIME_MODULE_NAME}/core-js/get-iterator`, "getIterator", "absoluteDefault"), [callee.object]);
-  },
-
-  BinaryExpression(node, parent, scope, file) {
-    // Symbol.iterator in arr -> core.$for.isIterable(arr)
-
-    if (node.operator !== "in") return;
-
-    var left = node.left;
-    if (!isSymbolIterator(left)) return;
-
-    return t.callExpression(
-      file.addImport(`${RUNTIME_MODULE_NAME}/core-js/is-iterable`, "isIterable", "absoluteDefault"),
-      [node.right]
-    );
-  },
-
-  MemberExpression: {
-    enter(node, parent, scope, file) {
-      // Array.from -> _core.Array.from
-
-      if (!this.isReferenced()) return;
-
-      var obj = node.object;
-      var prop = node.property;
-
-      if (!t.isReferenced(obj, node)) return;
-
-      if (node.computed) return;
-
-      if (!has(definitions.methods, obj.name)) return;
-
-      var methods = definitions.methods[obj.name];
-      if (!has(methods, prop.name)) return;
-
-      if (scope.getBindingIdentifier(obj.name)) return;
-
-      var modulePath = methods[prop.name];
-      return file.addImport(`${RUNTIME_MODULE_NAME}/core-js/${modulePath}`, `${obj.name}$${prop.name}`, "absoluteDefault");
-    },
-
-    exit(node, parent, scope, file) {
-      if (!this.isReferenced()) return;
-
-      var prop = node.property;
-      var obj  = node.object;
-
-      if (!has(definitions.builtins, obj.name)) return;
-      if (scope.getBindingIdentifier(obj.name)) return;
-
-      var modulePath = definitions.builtins[obj.name];
-      return t.memberExpression(
-        file.addImport(`${RUNTIME_MODULE_NAME}/core-js/${modulePath}`, `${obj.name}`, "absoluteDefault"),
-        prop
-      );
-    }
-  }
-});
-
-exports.metadata = {
-  optional: true
+export var metadata = {
+  optional: true,
+  group: "builtin-post-modules"
 };
 
-exports.Program = function (node, parent, scope, file) {
-  this.traverse(astVisitor, file);
-};
-
-exports.pre = function (file) {
+export function pre(file) {
   file.set("helperGenerator", function (name) {
     return file.addImport(`${RUNTIME_MODULE_NAME}/helpers/${name}`, name, "absoluteDefault");
   });
@@ -108,10 +22,84 @@ exports.pre = function (file) {
   file.setDynamic("regeneratorIdentifier", function () {
     return file.addImport(`${RUNTIME_MODULE_NAME}/regenerator`, "regeneratorRuntime", "absoluteDefault");
   });
-};
+}
 
-exports.Identifier = function (node, parent, scope, file) {
-  if (this.isReferencedIdentifier({ name: "regeneratorRuntime" })) {
+export function ReferencedIdentifier(node, parent, scope, file) {
+  if (node.name === "regeneratorRuntime") {
     return file.get("regeneratorIdentifier");
   }
+
+  if (t.isMemberExpression(parent)) return;
+  if (!has(definitions.builtins, node.name)) return;
+  if (scope.getBindingIdentifier(node.name)) return;
+
+  // 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) {
+  // arr[Symbol.iterator]() -> _core.$for.getIterator(arr)
+
+  if (node.arguments.length) return;
+
+  var callee = node.callee;
+  if (!t.isMemberExpression(callee)) return;
+  if (!callee.computed) return;
+  if (!this.get("callee.property").matchesPattern("Symbol.iterator")) return;
+
+  return t.callExpression(file.addImport(`${RUNTIME_MODULE_NAME}/core-js/get-iterator`, "getIterator", "absoluteDefault"), [callee.object]);
+}
+
+export function BinaryExpression(node, parent, scope, file) {
+  // Symbol.iterator in arr -> core.$for.isIterable(arr)
+
+  if (node.operator !== "in") return;
+  if (!this.get("left").matchesPattern("Symbol.iterator")) return;
+
+  return t.callExpression(
+    file.addImport(`${RUNTIME_MODULE_NAME}/core-js/is-iterable`, "isIterable", "absoluteDefault"),
+    [node.right]
+  );
+}
+
+export var MemberExpression = {
+  enter(node, parent, scope, file) {
+    // Array.from -> _core.Array.from
+
+    if (!this.isReferenced()) return;
+
+    var obj = node.object;
+    var prop = node.property;
+
+    if (!t.isReferenced(obj, node)) return;
+
+    if (node.computed) return;
+
+    if (!has(definitions.methods, obj.name)) return;
+
+    var methods = definitions.methods[obj.name];
+    if (!has(methods, prop.name)) return;
+
+    if (scope.getBindingIdentifier(obj.name)) return;
+
+    var modulePath = methods[prop.name];
+    return file.addImport(`${RUNTIME_MODULE_NAME}/core-js/${modulePath}`, `${obj.name}$${prop.name}`, "absoluteDefault");
+  },
+
+  exit(node, parent, scope, file) {
+    if (!this.isReferenced()) return;
+
+    var prop = node.property;
+    var obj  = node.object;
+
+    if (!has(definitions.builtins, obj.name)) return;
+    if (scope.getBindingIdentifier(obj.name)) return;
+
+    var modulePath = definitions.builtins[obj.name];
+    return t.memberExpression(
+      file.addImport(`${RUNTIME_MODULE_NAME}/core-js/${modulePath}`, `${obj.name}`, "absoluteDefault"),
+      prop
+    );
+  }
 };

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

@@ -1,26 +1,29 @@
 import * as messages from "../../../messages";
 import * as t from "../../../types";
 
-export function Program(program, parent, scope, file) {
-  var first = program.body[0];
-  if (t.isExpressionStatement(first) && t.isLiteral(first.expression, { value: "use strict" })) {
-    file.set("existingStrictDirective", program.body.shift());
+const THIS_BREAK_KEYS = ["FunctionExpression", "FunctionDeclaration", "ClassExpression", "ClassDeclaration"];
+
+export var Program = {
+  enter(program, parent, scope, file) {
+    var first = program.body[0];
+
+    var directive;
+    if (t.isExpressionStatement(first) && t.isLiteral(first.expression, { value: "use strict" })) {
+      directive = first;
+    } else {
+      directive = t.expressionStatement(t.literal("use strict"));
+      this.unshiftContainer("body", directive);
+      if (first) {
+        directive.leadingComments = first.leadingComments;
+        first.leadingComments = [];
+      }
+    }
+    directive._blockHoist = Infinity;
   }
 }
 
-export function FunctionExpression() {
-  this.skip();
-}
-
-export { FunctionExpression as FunctionDeclaration };
-export { FunctionExpression as Class };
-
 export function ThisExpression() {
-  return t.identifier("undefined");
-}
-
-export function CallExpression(node, parent, scope, file) {
-  if (t.isIdentifier(node.callee, { name: "eval" })) {
-    throw file.errorWithNode(node, messages.get("evalInStrictMode"));
+  if (!this.findParent((node) => !node.shadow && THIS_BREAK_KEYS.indexOf(node.type) >= 0)) {
+    return t.identifier("undefined");
   }
 }

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

@@ -23,21 +23,6 @@ function statementList(key, path, file) {
   }
 }
 
-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;

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

@@ -1 +1,11 @@
-export { bare as FunctionExpression, bare as ArrowFunctionExpression } from "../../helpers/name-method";
+import { bare } from "../../helpers/name-method";
+
+export var metadata = {
+  group: "builtin-setup"
+};
+
+export var FunctionExpression = {
+  exit: bare
+};
+
+export { FunctionExpression as ArrowFunctionExpression };

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

@@ -1,7 +1,8 @@
 import * as t from "../../../types";
 
 export var metadata = {
-  optional: true
+  optional: true,
+  group: "builtin-setup"
 };
 
 var match = t.buildMatchMemberExpression("process.env");

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

@@ -1,14 +1,6 @@
 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

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

src/babel/traversal/context.js

@@ -10,6 +10,11 @@ export default class TraversalContext {
     this.opts       = opts;
   }
 
+  shouldVisit(node) {
+    var keys = t.VISITOR_KEYS[node.type];
+    return !!(this.opts.enter || this.opts.exit || this.opts[node.type] || (keys && keys.length));
+  }
+
   create(node, obj, key) {
     return TraversalPath.get(this.parentPath, this, node, obj, key);
   }
@@ -25,7 +30,10 @@ export default class TraversalContext {
 
     // build up initial queue
     for (let i = 0; i < nodes.length; i++) {
-      if (nodes[i]) queue.push(this.create(node, nodes, i));
+      var self = nodes[i];
+      if (self && this.shouldVisit(self)) {
+        queue.push(this.create(node, nodes, i));
+      }
     }
 
     // visit the queue
@@ -42,16 +50,13 @@ export default class TraversalContext {
       }
     }
 
-    // clear context from queued paths
-    for (let i = 0; i < queue.length; i++) {
-      //queue[i].clearContext();
-    }
-
     return stop;
   }
 
   visitSingle(node, key) {
-    return this.create(node, node, key).visit();
+    if (this.shouldVisit(node[key])) {
+      return this.create(node, node, key).visit();
+    }
   }
 
   visit(node, key) {

src/babel/traversal/index.js

@@ -1,5 +1,5 @@
 import TraversalContext from "./context";
-import { explode, verify } from "./visitors";
+import * as visitors from "./visitors";
 import * as messages from "../messages";
 import includes from "lodash/collection/includes";
 import * as t from "../types";
@@ -14,7 +14,9 @@ export default function traverse(parent, opts, scope, state, parentPath) {
   }
 
   if (!opts) opts = {};
-  verify(opts);
+
+  visitors.verify(opts);
+  visitors.explode(opts);
 
   // array of nodes
   if (Array.isArray(parent)) {
@@ -26,8 +28,9 @@ export default function traverse(parent, opts, scope, state, parentPath) {
   }
 }
 
-traverse.verify = verify;
-traverse.explode = explode;
+traverse.visitors = visitors;
+traverse.verify = visitors.verify;
+traverse.explode = visitors.explode;
 
 traverse.node = function (node, opts, scope, state, parentPath) {
   var keys = t.VISITOR_KEYS[node.type];

src/babel/traversal/path/index.js

@@ -22,14 +22,14 @@ var hoistVariablesVisitor = explode({
   VariableDeclaration(node, parent, scope) {
     if (node.kind !== "var") return;
 
-      var bindings = this.getBindingIdentifiers();
+    var bindings = this.getBindingIdentifiers();
     for (var key in bindings) {
       scope.push({ id: bindings[key] });
     }
 
     var exprs = [];
 
-    for (var i = 0; i < node.declarations.length; i++) {
+    for (var declar of (node.declarations: Array)) {
       var declar = node.declarations[i];
       if (declar.init) {
         exprs.push(t.expressionStatement(
@@ -107,12 +107,78 @@ export default class TraversalPath {
     return ancestry;
   }
 
+  /**
+   * Description
+   */
+
+  inType(types) {
+    if (!Array.isArray(types)) types = [types];
+
+    var path = this;
+    while (path) {
+      for (var type of (types: Array)) {
+        if (path.node.type === type) return true;
+      }
+      path = path.parentPath;
+    }
+
+    return false;
+  }
+
+  /**
+   * Description
+   */
+
+  inShadow() {
+    var path = this;
+    while (path) {
+      if (path.isFunction()) {
+        if (path.node.shadow) {
+          return path;
+        } else {
+          return null;
+        }
+      }
+      path = path.parentPath;
+    }
+    return null;
+  }
+
+  /**
+   * Check whether this node was a part of the original AST.
+   */
+
+  isUser() {
+    return this.node && !!this.node.loc;
+  }
+
+  /**
+   * Check whether this node was generated by us and not a part of the original AST.
+   */
+
+  isGenerated() {
+    return !this.isUser();
+  }
+
+  /**
+   * Description
+   */
+
+  findParent(callback) {
+    var path = this;
+    while (path) {
+      if (callback(path.node, path)) return path;
+      path = path.parentPath;
+    }
+    return null;
+  }
+
   /**
    * Description
    */
 
   queueNode(path) {
-    if (this.context) {
+    if (this.context && this.context.queue) {
       this.context.queue.push(path);
     }
   }
@@ -136,7 +202,6 @@ export default class TraversalPath {
       } else if (this.isStatementOrBlock()) {
         if (this.node) nodes.push(this.node);
         this.container[this.key] = t.blockStatement(nodes);
-        this.checkSelf();
       } else {
         throw new Error("We don't know what to do with this node type. We were previously a Statement but we can't fit in here?");
       }
@@ -163,8 +228,6 @@ export default class TraversalPath {
         paths.push(TraversalPath.get(this, null, node, this.container, to));
       }
     }
-
-    this.checkPaths(paths);
   }
 
   _containerInsertBefore(nodes) {
@@ -234,7 +297,6 @@ export default class TraversalPath {
       } else if (this.isStatementOrBlock()) {
         if (this.node) nodes.unshift(this.node);
         this.container[this.key] = t.blockStatement(nodes);
-        this.checkSelf();
       } else {
         throw new Error("We don't know what to do with this node type. We were previously a Statement but we can't fit in here?");
       }
@@ -318,12 +380,44 @@ export default class TraversalPath {
     if (log) file.log.debug("End scope building");
   }
 
-  _remove() {
-    if (Array.isArray(this.container)) {
-      this.container.splice(this.key, 1);
-      this.updateSiblingKeys(this.key, -1);
+  /**
+   * Share comments amongst siblings.
+   */
+
+  shareCommentsWithSiblings() {
+    var node = this.node;
+    if (!node) return;
+
+    var trailing = node.trailingComments;
+    var leading  = node.leadingComments;
+    if (!trailing && !leading) return;
+
+    var prev = this.getSibling(this.key - 1);
+    var next = this.getSibling(this.key + 1);
+
+    if (!prev.node) prev = next;
+    if (!next.node) next = prev;
+
+    prev.giveComments("trailing", leading);
+    next.giveComments("leading", trailing);
+  }
+
+  /**
+   * Give node `comments` of the specified `type`.
+   */
+
+  giveComments(type: string, comments: Array) {
+    if (!comments) return;
+
+    var node = this.node;
+    if (!node) return;
+
+    var key = `${type}Comments`;
+
+    if (node[key]) {
+      node[key] = node[key].concat(comments);
     } else {
-      this.container[this.key] = null;
+      node[key] = comments;
     }
   }
 
@@ -332,6 +426,7 @@ export default class TraversalPath {
    */
 
   remove() {
+    this.shareCommentsWithSiblings();
     this._remove();
     this.removed = true;
 
@@ -366,6 +461,15 @@ export default class TraversalPath {
     }
   }
 
+  _remove() {
+    if (Array.isArray(this.container)) {
+      this.container.splice(this.key, 1);
+      this.updateSiblingKeys(this.key, -1);
+    } else {
+      this.container[this.key] = null;
+    }
+  }
+
   /**
    * Description
    */
@@ -528,7 +632,7 @@ export default class TraversalPath {
     }
 
     if (this.node === replacement) {
-      return this.checkSelf();
+      return;
     }
 
     // normalise inserting an entire AST
@@ -572,26 +676,6 @@ export default class TraversalPath {
 
     // potentially create new scope
     this.setScope();
-
-    this.checkSelf();
-  }
-
-  /**
-   * Description
-   */
-
-  checkSelf() {
-    this.checkPaths(this);
-  }
-
-  /**
-   * Description
-   */
-
-  checkPaths(paths) {
-    var scope = this.scope;
-    var file  = scope && scope.file;
-    if (file) file.checkPath(paths);
   }
 
   /**
@@ -680,20 +764,31 @@ export default class TraversalPath {
     if (!node) return;
 
     var opts = this.opts;
-    var fns  = [].concat(opts[key]);
+    if (!opts[key] && !opts[node.type]) return;
 
-    if (opts[node.type]) {
-      fns = fns.concat(opts[node.type][key]);
-    }
+    var fns = [].concat(opts[key]);
+    if (opts[node.type]) fns = fns.concat(opts[node.type][key]);
 
     for (var fn of (fns: Array)) {
       if (!fn) continue;
 
+      var node = this.node;
+      if (!node) return;
+
       // call the function with the params (node, parent, scope, state)
       var replacement = fn.call(this, node, this.parent, this.scope, this.state);
-      if (replacement) this.replaceWith(replacement, true);
+      var previousType = this.type;
 
-      if (this.shouldStop) break;
+      if (replacement) {
+        this.replaceWith(replacement, true);
+      }
+
+      if (this.shouldStop || this.shouldSkip || this.removed) return;
+
+      if (replacement && previousType !== this.type) {
+        this.queueNode(this);
+        return;
+      }
     }
   }
 
@@ -712,7 +807,7 @@ export default class TraversalPath {
 
   visit(): boolean {
     if (this.isBlacklisted()) return false;
-    if (this.opts.shouldSkip(this)) return false;
+    if (this.opts.shouldSkip && this.opts.shouldSkip(this)) return false;
 
     this.call("enter");
 
@@ -784,8 +879,7 @@ export default class TraversalPath {
 
   _getPattern(parts) {
     var path = this;
-    for (var i = 0; i > parts.length; i++) {
-      var part = parts[i];
+    for (var part of (parts: Array)) {
       if (part === ".") {
         path = path.parentPath;
       } else {
@@ -828,6 +922,14 @@ export default class TraversalPath {
     return !this.has(key);
   }
 
+  /**
+   * Description
+   */
+
+  equals(key, value): boolean {
+    return this.node[key] === value;
+  }
+
   /**
    * Description
    */
@@ -973,7 +1075,7 @@ export default class TraversalPath {
     var type     = typeInfo.annotation;
     if (!type) return false;
 
-    if (type.inferred && opts.inference === false) {
+    if (typeInfo.inferred && opts.inference === false) {
       return false;
     }
 

src/babel/traversal/scope.js

@@ -14,10 +14,10 @@ import * as t from "../types";
 var functionVariableVisitor = {
   enter(node, parent, scope, state) {
     if (t.isFor(node)) {
-      each(t.FOR_INIT_KEYS, (key) => {
+      for (var key of (t.FOR_INIT_KEYS: Array)) {
         var declar = this.get(key);
         if (declar.isVar()) state.scope.registerBinding("var", declar);
-      });
+      }
     }
 
     // this block is a function so we'll stop since none of the variables
@@ -48,13 +48,24 @@ var programReferenceVisitor = explode({
     }
   },
 
-  ExportDeclaration(node, parent, scope, state) {
-    var declar = node.declaration;
-    if (t.isClassDeclaration(declar) || t.isFunctionDeclaration(declar)) {
-      scope.getBinding(declar.id.name).reference();
-    } else if (t.isVariableDeclaration(declar)) {
-      for (var decl of (declar.declarations: Array)) {
-        scope.getBinding(decl.id.name).reference();
+  Scopable(node, parent, scope, state) {
+    for (var name in scope.bindings) {
+      state.references[name] = true;
+    }
+  },
+
+  ExportDeclaration: {
+    exit(node, parent, scope, state) {
+      var declar = node.declaration;
+      if (t.isClassDeclaration(declar) || t.isFunctionDeclaration(declar)) {
+        scope.getBinding(declar.id.name).reference();
+      } else if (t.isVariableDeclaration(declar)) {
+        for (var decl of (declar.declarations: Array)) {
+          var ids = t.getBindingIdentifiers(decl);
+          for (var name in ids) {
+            scope.getBinding(name).reference();
+          }
+        }
       }
     }
   },
@@ -90,50 +101,13 @@ var blockVariableVisitor = explode({
 
 var renameVisitor = explode({
   ReferencedIdentifier(node, parent, scope, state) {
-    if (node.name !== state.oldName) return;
-
-    if (this.parentPath.isProperty() && this.key === "key" && parent.shorthand) {
-      var value = t.identifier(state.newName);;
-
-      if (parent.value === state.binding) {
-        state.info.identifier = state.binding = value;
-      }
-
-      parent.shorthand = false;
-      parent.value = value;
-      parent.key = t.identifier(state.oldName);
-    } else {
+    if (node.name === state.oldName) {
       node.name = state.newName;
     }
   },
 
   Declaration(node, parent, scope, state) {
-    var ids = {};
-
-    var matchesLocal = (node, key) => {
-      return node.local === node[key] && (node.local.name === state.oldName || node.local.name === state.newName);
-    };
-
-    if (this.isExportDeclaration() && this.has("specifiers")) {
-      var specifiers = this.get("specifiers");
-      for (var specifier of (specifiers: Array)) {
-        if (specifier.isExportSpecifier() && matchesLocal(specifier.node, "exported")) {
-          specifier.get("exported").replaceWith(t.identifier(state.oldName));
-        }
-      }
-    } else if (this.isImportDeclaration() && this.has("specifiers")) {
-      var specifiers = this.get("specifiers");
-      for (var specifier of (specifiers: Array)) {
-        if (specifier.isImportSpecifier() && matchesLocal(specifier.node, "imported")) {
-          state.binding = state.info.identifier = t.identifier(state.newName);
-          specifier.get("local").replaceWith(state.binding);
-        } else {
-          extend(ids, specifier.getBindingIdentifiers());
-        }
-      }
-    } else {
-      ids = this.getBindingIdentifiers();
-    }
+    var ids = this.getBindingIdentifiers();;
 
     for (var name in ids) {
       if (name === state.oldName) ids[name].name = state.newName;
@@ -219,8 +193,13 @@ export default class Scope {
     do {
       uid = this._generateUid(name, i);
       i++;
-    } while (this.hasBinding(uid) || this.hasGlobal(uid) || this.hasUid(uid));
-    this.file.uids[uid] = true;
+    } while (this.hasBinding(uid) || this.hasGlobal(uid) || this.hasReference(uid));
+
+
+    var program = this.getProgramParent();
+    program.references[uid] = true;
+    program.uids[uid] = true;
+
     return uid;
   }
 
@@ -230,19 +209,6 @@ export default class Scope {
     return `_${id}`;
   }
 
-  /**
-   * Description
-   */
-
-  hasUid(name): boolean {
-    var scope = this;
-    do {
-      if (scope.file.uids[name]) return true;
-      scope = scope.parent;
-    } while (scope);
-    return false;
-  }
-
   /*
    * Description
    */
@@ -265,8 +231,8 @@ export default class Scope {
         if (node.source) {
           add(node.source);
         } else if (node.specifiers && node.specifiers.length) {
-          for (var i = 0; i < node.specifiers.length; i++) {
-            add(node.specifiers[i]);
+          for (var specifier of (node.specifiers: Array)) {
+            add(specifier);
           }
         } else if (node.declaration) {
           add(node.declaration);
@@ -283,8 +249,7 @@ export default class Scope {
       } else if (t.isCallExpression(node)) {
         add(node.callee);
       } else if (t.isObjectExpression(node) || t.isObjectPattern(node)) {
-        for (var i = 0; i < node.properties.length; i++) {
-          var prop = node.properties[i];
+        for (var prop of (node.properties: Array)) {
           add(prop.key || prop.argument);
         }
       }
@@ -398,7 +363,7 @@ export default class Scope {
 
     if (t.isIdentifier(node)) {
       var binding = this.getBinding(node.name);
-      if (binding && binding.isTypeGeneric("Array", { inference: false })) return node;
+      if (binding && binding.constant && binding.isTypeGeneric("Array")) return node;
     }
 
     if (t.isArrayExpression(node)) {
@@ -431,8 +396,8 @@ export default class Scope {
       this.registerBinding("hoisted", path);
     } else if (t.isVariableDeclaration(node)) {
       var declarations = path.get("declarations");
-      for (var i = 0; i < declarations.length; i++) {
-        this.registerBinding(node.kind, declarations[i]);
+      for (var declar of (declarations: Array)) {
+        this.registerBinding(node.kind, declar);
       }
     } else if (t.isClassDeclaration(node)) {
       this.registerBinding("let", path);
@@ -491,6 +456,20 @@ export default class Scope {
     this.globals[node.name] = node;
   }
 
+  /**
+   * Description
+   */
+
+  hasUid(name): boolean {
+    var scope = this;
+
+    do {
+      if (scope.uids[name]) return true;
+    } while (scope = scope.parent);
+
+    return false;
+  }
+
   /**
    * Description
    */
@@ -505,6 +484,20 @@ export default class Scope {
     return false;
   }
 
+  /**
+   * Description
+   */
+
+  hasReference(name: string): boolean {
+    var scope = this;
+
+    do {
+      if (scope.references[name]) return true;
+    } while (scope = scope.parent);
+
+    return false;
+  }
+
   /**
    * Description
    */
@@ -540,8 +533,10 @@ export default class Scope {
     if (info) return extend(this, info);
 
     info = this.block._scopeInfo = {
-      bindings: object(),
-      globals:  object()
+      references: object(),
+      bindings:   object(),
+      globals:    object(),
+      uids:       object(),
     };
 
     extend(this, info);
@@ -549,8 +544,8 @@ export default class Scope {
     // ForStatement - left, init
 
     if (path.isLoop()) {
-      for (let i = 0; i < t.FOR_INIT_KEYS.length; i++) {
-        var node = path.get(t.FOR_INIT_KEYS[i]);
+      for (let key of (t.FOR_INIT_KEYS: Array)) {
+        var node = path.get(key);
         if (node.isBlockScoped()) this.registerBinding(node.node.kind, node);
       }
     }
@@ -573,8 +568,8 @@ export default class Scope {
 
     if (path.isFunction()) {
       var params = path.get("params");
-      for (let i = 0; i < params.length; i++) {
-        this.registerBinding("param", params[i]);
+      for (let param of (params: Array)) {
+        this.registerBinding("param", param);
       }
       this.traverse(path.get("body").node, blockVariableVisitor, this);
     }
@@ -649,6 +644,18 @@ export default class Scope {
     declar.declarations.push(t.variableDeclarator(opts.id, opts.init));
   }
 
+  /**
+   * Walk up to the top of the scope tree and get the `Program`.
+   */
+
+  getProgramParent() {
+    var scope = this;
+    while (scope.parent) {
+      scope = scope.parent;
+    }
+    return scope;
+  }
+
   /**
    * Walk up the scope tree until we hit either a Function or reach the
    * very top and hit Program.
@@ -698,8 +705,7 @@ export default class Scope {
   getAllBindingsOfKind(): Object {
     var ids = object();
 
-    for (let i = 0; i < arguments.length; i++) {
-      var kind = arguments[i];
+    for (let kind of (arguments: Array)) {
       var scope = this;
       do {
         for (var name in scope.bindings) {
@@ -776,7 +782,7 @@ export default class Scope {
     if (!name) return false;
     if (this.hasOwnBinding(name)) return true;
     if (this.parentHasBinding(name)) return true;
-    if (this.file.uids[name]) return true;
+    if (this.hasUid(name)) return true;
     if (includes(Scope.globals, name)) return true;
     if (includes(Scope.contextVariables, name)) return true;
     return false;
@@ -790,6 +796,19 @@ export default class Scope {
     return this.parent && this.parent.hasBinding(name);
   }
 
+  /**
+   * Move a binding of `name` to another `scope`.
+   */
+
+  moveBindingTo(name, scope) {
+    var info = this.getBinding(name);
+    if (info) {
+      info.scope.removeOwnBinding(name);
+      info.scope = scope;
+      scope.bindings[name] = info;
+    }
+  }
+
   /**
    * Description
    */

src/babel/traversal/visitors.js

@@ -4,6 +4,9 @@ import * as t from "../types";
 import esquery from "esquery";
 
 export function explode(visitor, mergeConflicts) {
+  if (visitor._exploded) return visitor;
+  visitor._exploded = true;
+
   // 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;
@@ -36,12 +39,12 @@ export function explode(visitor, mergeConflicts) {
     if (wrapper.type) {
       // merge the visitor if necessary or just put it back in
       if (visitor[wrapper.type]) {
-        merge(visitor[wrapper.type], fns);
+        mergePair(visitor[wrapper.type], fns);
       } else {
         visitor[wrapper.type] = fns;
       }
     } else {
-      merge(visitor, fns);
+      mergePair(visitor, fns);
     }
   }
 
@@ -61,7 +64,7 @@ export function explode(visitor, mergeConflicts) {
       var existing = visitor[alias];
       if (existing) {
         if (mergeConflicts) {
-          merge(existing, fns);
+          mergePair(existing, fns);
         }
       } else {
         visitor[alias] = fns;
@@ -79,22 +82,15 @@ export function verify(visitor) {
     throw new Error(messages.get("traverseVerifyRootFunction"));
   }
 
-  if (!visitor.enter) visitor.enter = function () { };
-  if (!visitor.exit) visitor.exit = function () { };
-  if (!visitor.shouldSkip) visitor.shouldSkip = function () { return false; };
-
   for (var nodeType in visitor) {
     if (shouldIgnoreKey(nodeType)) continue;
 
-    if (t.TYPES.indexOf(nodeType) < 0) {
+    if (t.TYPES.indexOf(nodeType) < 0 && !virtualTypes[nodeType]) {
       throw new Error(messages.get("traverseVerifyNodeType", nodeType));
     }
 
     var visitors = visitor[nodeType];
-
-    if (typeof visitors === "function") {
-      throw new Error(messages.get("traverseVerifyVisitorFunction", nodeType));
-    } else if (typeof visitors === "object") {
+    if (typeof visitors === "object") {
       for (var visitorKey in visitors) {
         if (visitorKey === "enter" || visitorKey === "exit") continue;
         throw new Error(messages.get("traverseVerifyVisitorProperty", nodeType, visitorKey));
@@ -105,6 +101,19 @@ export function verify(visitor) {
   visitor._verified = true;
 }
 
+export function merge(visitors) {
+  var rootVisitor = {};
+
+  for (var visitor of (visitors: Array)) {
+    for (var type in visitor) {
+      var nodeVisitor = rootVisitor[type] = rootVisitor[type] || {};
+      mergePair(nodeVisitor, visitor[type]);
+    }
+  }
+
+  return rootVisitor;
+}
+
 function ensureEntranceObjects(obj) {
   for (let key in obj) {
     if (shouldIgnoreKey(key)) continue;
@@ -135,7 +144,7 @@ function addSelector(visitor, selector, fns) {
     };
   }
 
-  merge(visitor, fns);
+  mergePair(visitor, fns);
 }
 
 function wrapCheck(wrapper, fn) {
@@ -159,7 +168,7 @@ function shouldIgnoreKey(key) {
   return false;
 }
 
-function merge(dest, src) {
+function mergePair(dest, src) {
   for (var key in src) {
     dest[key] = (dest[key] || []).concat(src[key]);
   }

src/babel/types/alias-keys.json

@@ -26,9 +26,9 @@
   "ExportNamedDeclaration":     ["Statement", "Declaration", "ModuleDeclaration", "ExportDeclaration"],
   "ImportDeclaration":          ["Statement", "Declaration", "ModuleDeclaration"],
 
-  "ArrowFunctionExpression": ["Scopable", "Function", "Expression", "Pure"],
-  "FunctionDeclaration":     ["Scopable", "Function", "Statement", "Pure", "Declaration"],
-  "FunctionExpression":      ["Scopable", "Function", "Expression", "Pure"],
+  "ArrowFunctionExpression": ["Scopable", "Function", "Func", "Expression", "Pure"],
+  "FunctionDeclaration":     ["Scopable", "Function", "Func", "Statement", "Pure", "Declaration"],
+  "FunctionExpression":      ["Scopable", "Function", "Func", "Expression", "Pure"],
 
   "BlockStatement": ["Scopable", "Statement"],
   "Program":        ["Scopable"],

src/babel/types/converters.js

@@ -51,7 +51,7 @@ export function toSequenceExpression(nodes: Array<Object>, scope: Scope): Object
       } else if (t.isVariableDeclaration(node)) {
         if (node.kind !== "var") return bailed = true; // bailed
 
-        each(node.declarations, function (declar) {
+        for (var declar of (node.declarations: Array)) {
           var bindings = t.getBindingIdentifiers(declar);
           for (var key in bindings) {
             declars.push({
@@ -63,7 +63,7 @@ export function toSequenceExpression(nodes: Array<Object>, scope: Scope): Object
           if (declar.init) {
             exprs.push(t.assignmentExpression("=", declar.id, declar.init));
           }
-        });
+        }
 
         ensureLastUndefined = true;
         continue;

src/babel/types/index.js

@@ -79,6 +79,8 @@ export function isType(nodeType, targetType) {
 
   var aliases = t.FLIPPED_ALIAS_KEYS[targetType];
   if (aliases) {
+    if (aliases[0] === nodeType) return true;
+
     for (var alias of (aliases: Array)) {
       if (nodeType === alias) return true;
     }
@@ -258,9 +260,9 @@ export function buildMatchMemberExpression(match:string, allowPartial?: boolean)
  */
 
 export function removeComments(child: Object): Object {
-  each(COMMENT_KEYS, function (key) {
+  for (var key of (COMMENT_KEYS: Array)) {
     delete child[key];
-  });
+  }
   return child;
 }
 
@@ -270,9 +272,9 @@ export function removeComments(child: Object): Object {
 
 export function inheritsComments(child: Object, parent: Object): Object {
   if (child && parent) {
-    each(COMMENT_KEYS, function (key) {
+    for (var key of (COMMENT_KEYS: Array)) {
       child[key]  = uniq(compact([].concat(child[key], parent[key])));
-    });
+    }
   }
   return child;
 }