From 6f664ca64e9e76683fa52c97e0148d8e857933ae Mon Sep 17 00:00:00 2001
From: Sebastian McKenzie <sebmck@gmail.com>
Date: Thu, 7 May 2015 15:53:22 +0100
Subject: [PATCH] merge internal transformers into single traversal pass

---
 src/babel/transformation/file/index.js        | 76 ++++++++++---------
 ...-binary-assignment-operator-transformer.js |  4 -
 .../helpers/build-react-transformer.js        |  6 --
 src/babel/transformation/index.js             |  7 ++
 src/babel/transformation/transformer-pass.js  | 19 ++---
 src/babel/transformation/transformer.js       | 13 ----
 .../transformers/es5/properties.mutators.js   | 42 +++++-----
 .../transformers/es6/arrow-functions.js       |  2 -
 .../transformers/es6/block-scoping.js         |  4 -
 .../transformers/es6/classes.js               | 10 +--
 .../transformers/es6/constants.js             |  4 -
 .../transformers/es6/destructuring.js         |  5 --
 .../transformation/transformers/es6/for-of.js |  2 -
 .../transformers/es6/modules.js               |  2 -
 .../transformers/es6/object-super.js          |  2 -
 .../transformers/es6/parameters.default.js    |  6 --
 .../transformers/es6/parameters.rest.js       |  4 -
 .../transformers/es6/properties.computed.js   | 70 +++++++++--------
 .../transformers/es6/properties.shorthand.js  |  4 -
 .../transformers/es6/regex.sticky.js          |  4 -
 .../transformers/es6/regex.unicode.js         |  4 -
 .../transformation/transformers/es6/spread.js |  2 -
 .../transformers/es6/template-literals.js     |  4 -
 .../transformers/es7/async-functions.js       |  4 -
 .../transformers/es7/class-properties.js      |  4 -
 .../transformers/es7/decorators.js            |  4 -
 .../transformers/es7/do-expressions.js        |  2 -
 .../transformers/es7/export-extensions.js     |  4 -
 .../es7/trailing-function-commas.js           |  4 -
 .../transformation/transformers/index.js      | 66 +---------------
 .../transformers/internal/hoist-directives.js | 16 ++++
 .../transformers/internal/module-formatter.js |  2 -
 .../transformers/internal/modules.js          |  4 -
 .../transformers/internal/shadow-functions.js | 29 +++----
 .../transformers/internal/strict.js           | 19 -----
 .../transformers/internal/validation.js       | 17 -----
 .../transformers/optimisation/flow.for-of.js  |  1 -
 .../transformation/transformers/other/flow.js |  4 -
 .../transformers/other/regenerator.js         |  8 +-
 .../transformers/other/strict.js              | 35 ++++++---
 .../spec/block-scoped-functions.js            | 15 ----
 .../transformers/validation/react.js          |  8 --
 .../validation/undeclared-variable-check.js   |  3 +-
 src/babel/traversal/index.js                  |  9 ++-
 src/babel/traversal/path/index.js             | 67 +++++++++-------
 src/babel/traversal/visitors.js               | 23 ++++--
 .../es6.arrow-functions/arguments/expected.js | 10 +--
 .../assignment-expression/expected.js         |  6 +-
 48 files changed, 243 insertions(+), 417 deletions(-)
 create mode 100644 src/babel/transformation/transformers/internal/hoist-directives.js
 delete mode 100644 src/babel/transformation/transformers/internal/strict.js

diff --git a/src/babel/transformation/file/index.js b/src/babel/transformation/file/index.js
index bec58c718a..bb2d3697db 100644
--- a/src/babel/transformation/file/index.js
+++ b/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";
@@ -26,19 +27,6 @@ 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.dynamicImportTypes = {};
@@ -234,7 +222,46 @@ export default class File {
     stack = beforePlugins.concat(stack, afterPlugins);
 
     // register
-    this.transformerStack = stack.concat(secondaryStack);
+    this.transformerStack = this.mergeStack(stack.concat(secondaryStack));
+
+
+  }
+
+  mergeStack(_stack) {
+    var stack  = [];
+    var ignore = [];
+
+    for (let pass of (_stack: Array)) {
+      // been merged
+      if (ignore.indexOf(pass) >= 0) continue;
+
+      var category = pass.transformer.metadata.category;
+
+      // can't merge
+      if (!pass.canTransform() || !category) {
+        stack.push(pass);
+        continue;
+      }
+
+      var mergeStack = [];
+      for (let pass of (_stack: Array)) {
+        if (pass.transformer.metadata.category === category) {
+          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(category, visitor);
+      //console.log(mergeTransformer);
+      stack.push(mergeTransformer.buildPass(this));
+    }
+
+    return stack;
   }
 
   set(key: string, val): any {
@@ -357,23 +384,6 @@ 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 +471,6 @@ 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()) {
diff --git a/src/babel/transformation/helpers/build-binary-assignment-operator-transformer.js b/src/babel/transformation/helpers/build-binary-assignment-operator-transformer.js
index 45a6d812c5..04ffc4c1b3 100644
--- a/src/babel/transformation/helpers/build-binary-assignment-operator-transformer.js
+++ b/src/babel/transformation/helpers/build-binary-assignment-operator-transformer.js
@@ -10,10 +10,6 @@ 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;
diff --git a/src/babel/transformation/helpers/build-react-transformer.js b/src/babel/transformation/helpers/build-react-transformer.js
index 46a9bdfef7..c63bd60882 100644
--- a/src/babel/transformation/helpers/build-react-transformer.js
+++ b/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();
diff --git a/src/babel/transformation/index.js b/src/babel/transformation/index.js
index 442ed37849..3f71068bc2 100644
--- a/src/babel/transformation/index.js
+++ b/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.category = metadata.category || "builtin";
+}
+
 pipeline.addTransformers(transformers);
 
 //
diff --git a/src/babel/transformation/transformer-pass.js b/src/babel/transformation/transformer-pass.js
index 38c3e8ef8c..715ba6de2e 100644
--- a/src/babel/transformation/transformer-pass.js
+++ b/src/babel/transformation/transformer-pass.js
@@ -8,27 +8,18 @@ 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.skipKey     = transformer.skipKey;
+    this.file        = file;
+    this.ran         = false;
   }
 
   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);
-  }
-
   transform() {
-    if (!this.shouldTransform) return;
-
     var file = this.file;
 
     file.log.debug(`Start transformer ${this.transformer.key}`);
diff --git a/src/babel/transformation/transformer.js b/src/babel/transformation/transformer.js
index 3e12abcf1d..a5fac03bf9 100644
--- a/src/babel/transformation/transformer.js
+++ b/src/babel/transformation/transformer.js
@@ -25,7 +25,6 @@ export default class Transformer {
     };
 
     this.manipulateOptions = take("manipulateOptions");
-    this.shouldVisit       = take("shouldVisit");
     this.metadata          = take("metadata") || {};
     this.parser            = take("parser");
     this.post              = take("post");
@@ -41,18 +40,6 @@ 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 {
diff --git a/src/babel/transformation/transformers/es5/properties.mutators.js b/src/babel/transformation/transformers/es5/properties.mutators.js
index 9b1deb2870..7fe77c7f41 100644
--- a/src/babel/transformation/transformers/es5/properties.mutators.js
+++ b/src/babel/transformation/transformers/es5/properties.mutators.js
@@ -1,28 +1,26 @@
 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 var ObjectExpression = {
+  exit(node, parent, scope, file) {
+    var mutatorMap = {};
+    var hasAny = false;
 
-export function ObjectExpression(node, parent, scope, file) {
-  var mutatorMap = {};
-  var hasAny = false;
+    node.properties = node.properties.filter(function (prop) {
+      if (prop.kind === "get" || prop.kind === "set") {
+        hasAny = true;
+        defineMap.push(mutatorMap, prop, prop.kind, file);
+        return false;
+      } else {
+        return true;
+      }
+    });
 
-  node.properties = node.properties.filter(function (prop) {
-    if (prop.kind === "get" || prop.kind === "set") {
-      hasAny = true;
-      defineMap.push(mutatorMap, prop, prop.kind, file);
-      return false;
-    } else {
-      return true;
-    }
-  });
+    if (!hasAny) return;
 
-  if (!hasAny) return;
-
-  return t.callExpression(
-    t.memberExpression(t.identifier("Object"), t.identifier("defineProperties")),
-    [node, defineMap.toDefineObject(mutatorMap)]
-  );
-}
+    return t.callExpression(
+      t.memberExpression(t.identifier("Object"), t.identifier("defineProperties")),
+      [node, defineMap.toDefineObject(mutatorMap)]
+    );
+  }
+};
diff --git a/src/babel/transformation/transformers/es6/arrow-functions.js b/src/babel/transformation/transformers/es6/arrow-functions.js
index d40d436727..39d93f829a 100644
--- a/src/babel/transformation/transformers/es6/arrow-functions.js
+++ b/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);
 
diff --git a/src/babel/transformation/transformers/es6/block-scoping.js b/src/babel/transformation/transformers/es6/block-scoping.js
index 1b81d95232..850dca35f0 100644
--- a/src/babel/transformation/transformers/es6/block-scoping.js
+++ b/src/babel/transformation/transformers/es6/block-scoping.js
@@ -37,10 +37,6 @@ function standardizeLets(declars) {
   }
 }
 
-export function shouldVisit(node) {
-  return t.isVariableDeclaration(node) && (node.kind === "let" || node.kind === "const");
-}
-
 export function VariableDeclaration(node, parent, scope, file) {
   if (!isLet(node, parent)) return;
 
diff --git a/src/babel/transformation/transformers/es6/classes.js b/src/babel/transformation/transformers/es6/classes.js
index 670a18b5fb..e1bb106659 100644
--- a/src/babel/transformation/transformers/es6/classes.js
+++ b/src/babel/transformation/transformers/es6/classes.js
@@ -11,17 +11,17 @@ 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))
   ]);
 }
 
-export function ClassExpression(node, parent, scope, file) {
-  return new ClassTransformer(this, file).run();
-}
+export var ClassExpression = {
+  exit(node, parent, scope, file) {
+    return new ClassTransformer(this, file).run();
+  }
+};
 
 var collectPropertyReferencesVisitor = {
   Identifier: {
diff --git a/src/babel/transformation/transformers/es6/constants.js b/src/babel/transformation/transformers/es6/constants.js
index b8df344bfb..4125b68d10 100644
--- a/src/babel/transformation/transformers/es6/constants.js
+++ b/src/babel/transformation/transformers/es6/constants.js
@@ -1,10 +1,6 @@
 import * as messages from "../../../messages";
 import * as t from "../../../types";
 
-export function shouldVisit(node) {
-  return t.isVariableDeclaration(node, { kind: "const" }) || t.isImportDeclaration(node);
-}
-
 var visitor = {
   enter(node, parent, scope, state) {
     if (this.isAssignmentExpression() || this.isUpdateExpression()) {
diff --git a/src/babel/transformation/transformers/es6/destructuring.js b/src/babel/transformation/transformers/es6/destructuring.js
index 5dd84da762..5fb2df518b 100644
--- a/src/babel/transformation/transformers/es6/destructuring.js
+++ b/src/babel/transformation/transformers/es6/destructuring.js
@@ -1,8 +1,6 @@
 import * as messages from "../../../messages";
 import * as t from "../../../types";
 
-export var shouldVisit = t.isPattern;
-
 export function ForOfStatement(node, parent, scope, file) {
   var left = node.left;
 
@@ -83,7 +81,6 @@ 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) {
@@ -104,8 +101,6 @@ 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) {
diff --git a/src/babel/transformation/transformers/es6/for-of.js b/src/babel/transformation/transformers/es6/for-of.js
index 7d007d6465..b986492da9 100644
--- a/src/babel/transformation/transformers/es6/for-of.js
+++ b/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);
diff --git a/src/babel/transformation/transformers/es6/modules.js b/src/babel/transformation/transformers/es6/modules.js
index 5abf2b1af4..6141ab9217 100644
--- a/src/babel/transformation/transformers/es6/modules.js
+++ b/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++) {
diff --git a/src/babel/transformation/transformers/es6/object-super.js b/src/babel/transformation/transformers/es6/object-super.js
index b261520da2..10d01e09f8 100644
--- a/src/babel/transformation/transformers/es6/object-super.js
+++ b/src/babel/transformation/transformers/es6/object-super.js
@@ -1,8 +1,6 @@
 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;
 
diff --git a/src/babel/transformation/transformers/es6/parameters.default.js b/src/babel/transformation/transformers/es6/parameters.default.js
index 56345ee839..165c177844 100644
--- a/src/babel/transformation/transformers/es6/parameters.default.js
+++ b/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;
@@ -96,6 +92,4 @@ exports.Function = function (node, parent, scope, file) {
   } else {
     node.body.body = body.concat(node.body.body);
   }
-
-  this.checkSelf();
 };
diff --git a/src/babel/transformation/transformers/es6/parameters.rest.js b/src/babel/transformation/transformers/es6/parameters.rest.js
index 631701a766..6b57c156a3 100644
--- a/src/babel/transformation/transformers/es6/parameters.rest.js
+++ b/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
@@ -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();
 };
diff --git a/src/babel/transformation/transformers/es6/properties.computed.js b/src/babel/transformation/transformers/es6/properties.computed.js
index e846e4d2a6..d944844ca0 100644
--- a/src/babel/transformation/transformers/es6/properties.computed.js
+++ b/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 i = 0; i < node.properties.length; i++) {
+      hasComputed = t.isProperty(node.properties[i], { 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;
-}
+};
diff --git a/src/babel/transformation/transformers/es6/properties.shorthand.js b/src/babel/transformation/transformers/es6/properties.shorthand.js
index 5f6830cfb7..b5140ac364 100644
--- a/src/babel/transformation/transformers/es6/properties.shorthand.js
+++ b/src/babel/transformation/transformers/es6/properties.shorthand.js
@@ -1,9 +1,5 @@
 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;
diff --git a/src/babel/transformation/transformers/es6/regex.sticky.js b/src/babel/transformation/transformers/es6/regex.sticky.js
index 3227c59635..e298e0501b 100644
--- a/src/babel/transformation/transformers/es6/regex.sticky.js
+++ b/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"), [
diff --git a/src/babel/transformation/transformers/es6/regex.unicode.js b/src/babel/transformation/transformers/es6/regex.unicode.js
index 58471da84a..a914f2b529 100644
--- a/src/babel/transformation/transformers/es6/regex.unicode.js
+++ b/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);
diff --git a/src/babel/transformation/transformers/es6/spread.js b/src/babel/transformation/transformers/es6/spread.js
index a856453ed0..e7c403588a 100644
--- a/src/babel/transformation/transformers/es6/spread.js
+++ b/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;
diff --git a/src/babel/transformation/transformers/es6/template-literals.js b/src/babel/transformation/transformers/es6/template-literals.js
index 10128abaf7..912fcdbbdf 100644
--- a/src/babel/transformation/transformers/es6/template-literals.js
+++ b/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  = [];
diff --git a/src/babel/transformation/transformers/es7/async-functions.js b/src/babel/transformation/transformers/es7/async-functions.js
index df6bc46bd4..5059fdd666 100644
--- a/src/babel/transformation/transformers/es7/async-functions.js
+++ b/src/babel/transformation/transformers/es7/async-functions.js
@@ -1,7 +1,3 @@
 export var metadata = {
   stage: 1
 };
-
-export function shouldVisit() {
-  return false;
-}
diff --git a/src/babel/transformation/transformers/es7/class-properties.js b/src/babel/transformation/transformers/es7/class-properties.js
index 9c08f42ae1..871398b386 100644
--- a/src/babel/transformation/transformers/es7/class-properties.js
+++ b/src/babel/transformation/transformers/es7/class-properties.js
@@ -1,7 +1,3 @@
 export var metadata = {
   stage: 0
 };
-
-export function shouldVisit() {
-  return false;
-}
diff --git a/src/babel/transformation/transformers/es7/decorators.js b/src/babel/transformation/transformers/es7/decorators.js
index a67843cf3d..af98294cf8 100644
--- a/src/babel/transformation/transformers/es7/decorators.js
+++ b/src/babel/transformation/transformers/es7/decorators.js
@@ -7,10 +7,6 @@ export var metadata = {
   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++) {
diff --git a/src/babel/transformation/transformers/es7/do-expressions.js b/src/babel/transformation/transformers/es7/do-expressions.js
index 8f1e18875f..efefe06ba2 100644
--- a/src/babel/transformation/transformers/es7/do-expressions.js
+++ b/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) {
diff --git a/src/babel/transformation/transformers/es7/export-extensions.js b/src/babel/transformation/transformers/es7/export-extensions.js
index 80a11c34ab..77880f3a10 100644
--- a/src/babel/transformation/transformers/es7/export-extensions.js
+++ b/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;
diff --git a/src/babel/transformation/transformers/es7/trailing-function-commas.js b/src/babel/transformation/transformers/es7/trailing-function-commas.js
index df6bc46bd4..5059fdd666 100644
--- a/src/babel/transformation/transformers/es7/trailing-function-commas.js
+++ b/src/babel/transformation/transformers/es7/trailing-function-commas.js
@@ -1,7 +1,3 @@
 export var metadata = {
   stage: 1
 };
-
-export function shouldVisit() {
-  return false;
-}
diff --git a/src/babel/transformation/transformers/index.js b/src/babel/transformation/transformers/index.js
index 05f7c47c41..0c3ea89b1d 100644
--- a/src/babel/transformation/transformers/index.js
+++ b/src/babel/transformation/transformers/index.js
@@ -1,124 +1,66 @@
 export default {
   "utility.removeDebugger":                require("./utility/remove-debugger"),
   "utility.removeConsole":                 require("./utility/remove-console"),
-
   "utility.inlineEnvironmentVariables":    require("./utility/inline-environment-variables"),
   "utility.inlineExpressions":             require("./utility/inline-expressions"),
-
   "minification.deadCodeElimination":      require("./minification/dead-code-elimination"),
-
   _modules:                                require("./internal/modules"),
-
   "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"),
-
-  // needs to be before `es6.blockScoping` as let variables may be produced
   "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"),
-
   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
+  runtime:                                 require("./other/runtime"),
   "es7.exportExtensions":                  require("./es7/export-extensions"),
   "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"),
-
   "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")
+  flow:                                    require("./other/flow"),
+  _hoistDirectives:                        require("./internal/hoist-directives"),
+  _blockHoist:                             require("./internal/block-hoist")
 };
diff --git a/src/babel/transformation/transformers/internal/hoist-directives.js b/src/babel/transformation/transformers/internal/hoist-directives.js
new file mode 100644
index 0000000000..8c0c1280cf
--- /dev/null
+++ b/src/babel/transformation/transformers/internal/hoist-directives.js
@@ -0,0 +1,16 @@
+import * as t from "../../../types";
+
+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 };
diff --git a/src/babel/transformation/transformers/internal/module-formatter.js b/src/babel/transformation/transformers/internal/module-formatter.js
index 92ef7baab2..400f27e28a 100644
--- a/src/babel/transformation/transformers/internal/module-formatter.js
+++ b/src/babel/transformation/transformers/internal/module-formatter.js
@@ -1,8 +1,6 @@
 import * as strict from "../../helpers/strict";
 
 export function Program(program, parent, scope, file) {
-  this.stop();
-
   strict.wrap(program, function () {
     program.body = file.dynamicImports.concat(program.body);
   });
diff --git a/src/babel/transformation/transformers/internal/modules.js b/src/babel/transformation/transformers/internal/modules.js
index 5953072c27..6d3dfe83c8 100644
--- a/src/babel/transformation/transformers/internal/modules.js
+++ b/src/babel/transformation/transformers/internal/modules.js
@@ -6,10 +6,6 @@
 
 import * as t from "../../../types";
 
-export function shouldVisit(node) {
-  return t.isImportDeclaration(node) || t.isExportDeclaration(node);
-}
-
 export function ImportDeclaration(node, parent, scope, file) {
   if (node.source) {
     node.source.value = file.resolveModuleSource(node.source.value);
diff --git a/src/babel/transformation/transformers/internal/shadow-functions.js b/src/babel/transformation/transformers/internal/shadow-functions.js
index 4eb4e5e375..30925d8a8f 100644
--- a/src/babel/transformation/transformers/internal/shadow-functions.js
+++ b/src/babel/transformation/transformers/internal/shadow-functions.js
@@ -82,21 +82,24 @@ function aliasFunction(getBody, path, scope) {
   }
 };
 
-export function shouldVisit(node) {
-  return true;
-}
+// todo: on all `this` and `arguments`, walk UP the tree instead of
+// crawling the entire function tree
 
-export function Program(node, parent, scope) {
-  aliasFunction(function () {
-    return node.body;
-  }, this, scope);
+export var Program = {
+  exit(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 var FunctionDeclaration = {
+  exit(node, parent, scope) {
+    aliasFunction(function () {
+      t.ensureBlock(node);
+      return node.body.body;
+    }, this, scope);
+  }
+};
 
 export { FunctionDeclaration as FunctionExpression };
diff --git a/src/babel/transformation/transformers/internal/strict.js b/src/babel/transformation/transformers/internal/strict.js
deleted file mode 100644
index afc820c665..0000000000
--- a/src/babel/transformation/transformers/internal/strict.js
+++ /dev/null
@@ -1,19 +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]);
-  }
-  this.stop();
-}
diff --git a/src/babel/transformation/transformers/internal/validation.js b/src/babel/transformation/transformers/internal/validation.js
index 8fab413fdd..da830eabef 100644
--- a/src/babel/transformation/transformers/internal/validation.js
+++ b/src/babel/transformation/transformers/internal/validation.js
@@ -1,10 +1,6 @@
 import * as messages from "../../../messages";
 import * as t from "../../../types";
 
-export var metadata = {
-  readOnly: true
-};
-
 export function ForOfStatement(node, parent, scope, file) {
   var left = node.left;
   if (t.isVariableDeclaration(left)) {
@@ -43,16 +39,3 @@ 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 };
diff --git a/src/babel/transformation/transformers/optimisation/flow.for-of.js b/src/babel/transformation/transformers/optimisation/flow.for-of.js
index f69525e307..0f031a9b51 100644
--- a/src/babel/transformation/transformers/optimisation/flow.for-of.js
+++ b/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
 };
diff --git a/src/babel/transformation/transformers/other/flow.js b/src/babel/transformation/transformers/other/flow.js
index b3a963e3cc..bb6bf4c393 100644
--- a/src/babel/transformation/transformers/other/flow.js
+++ b/src/babel/transformation/transformers/other/flow.js
@@ -1,9 +1,5 @@
 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();
 }
diff --git a/src/babel/transformation/transformers/other/regenerator.js b/src/babel/transformation/transformers/other/regenerator.js
index 7c109a92a5..2897527cd1 100644
--- a/src/babel/transformation/transformers/other/regenerator.js
+++ b/src/babel/transformation/transformers/other/regenerator.js
@@ -1,14 +1,8 @@
 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) {
+  exit(ast) {
     regenerator.transform(ast);
-    this.stop();
-    this.checkSelf();
   }
 };
diff --git a/src/babel/transformation/transformers/other/strict.js b/src/babel/transformation/transformers/other/strict.js
index 1c8acc2651..1889800b11 100644
--- a/src/babel/transformation/transformers/other/strict.js
+++ b/src/babel/transformation/transformers/other/strict.js
@@ -1,22 +1,33 @@
 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");
+  if (!this.findParent(function (node) {
+    return !node.shadow && THIS_BREAK_KEYS.indexOf(node.type) >= 0;
+  })) {
+    return t.identifier("undefined");
+  }
 }
 
 export function CallExpression(node, parent, scope, file) {
diff --git a/src/babel/transformation/transformers/spec/block-scoped-functions.js b/src/babel/transformation/transformers/spec/block-scoped-functions.js
index b5327d8c0f..ae16f05fcb 100644
--- a/src/babel/transformation/transformers/spec/block-scoped-functions.js
+++ b/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;
diff --git a/src/babel/transformation/transformers/validation/react.js b/src/babel/transformation/transformers/validation/react.js
index 5666f8c299..536aff1768 100644
--- a/src/babel/transformation/transformers/validation/react.js
+++ b/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)) {
diff --git a/src/babel/transformation/transformers/validation/undeclared-variable-check.js b/src/babel/transformation/transformers/validation/undeclared-variable-check.js
index 01f1f4a86c..f8d3b25a78 100644
--- a/src/babel/transformation/transformers/validation/undeclared-variable-check.js
+++ b/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) {
diff --git a/src/babel/traversal/index.js b/src/babel/traversal/index.js
index 1f2ccccf12..80cb1f0c93 100644
--- a/src/babel/traversal/index.js
+++ b/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 +14,7 @@ export default function traverse(parent, opts, scope, state, parentPath) {
   }
 
   if (!opts) opts = {};
-  verify(opts);
+  visitors.verify(opts);
 
   // array of nodes
   if (Array.isArray(parent)) {
@@ -26,8 +26,9 @@ 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];
diff --git a/src/babel/traversal/path/index.js b/src/babel/traversal/path/index.js
index 14b801de53..23b971a900 100644
--- a/src/babel/traversal/path/index.js
+++ b/src/babel/traversal/path/index.js
@@ -107,12 +107,43 @@ 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
+   */
+
+  findParent(callback) {
+    var path = this;
+    while (path) {
+      if (callback(path.node)) return path.node;
+      path = path.parentPath;
+    }
+    return null;
+  }
+
   /**
    * Description
    */
 
   queueNode(path) {
-    if (this.context) {
+    if (this.context && this.context.queue) {
       this.context.queue.push(path);
     }
   }
@@ -136,7 +167,6 @@ 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 +193,6 @@ export default class TraversalPath {
         paths.push(TraversalPath.get(this, null, node, this.container, to));
       }
     }
-
-    this.checkPaths(paths);
   }
 
   _containerInsertBefore(nodes) {
@@ -234,7 +262,6 @@ 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?");
       }
@@ -528,7 +555,7 @@ export default class TraversalPath {
     }
 
     if (this.node === replacement) {
-      return this.checkSelf();
+      return;
     }
 
     // normalise inserting an entire AST
@@ -572,26 +599,6 @@ 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);
   }
 
   /**
@@ -691,9 +698,13 @@ export default class TraversalPath {
 
       // 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);
+      if (replacement) {
+        this.replaceWith(replacement, true);
+        this.queueNode(this);
+        break;
+      }
 
-      if (this.shouldStop) break;
+      if (this.shouldStop || this.removed) break;
     }
   }
 
diff --git a/src/babel/traversal/visitors.js b/src/babel/traversal/visitors.js
index 8e994c1ccb..f922351d1f 100644
--- a/src/babel/traversal/visitors.js
+++ b/src/babel/traversal/visitors.js
@@ -36,12 +36,12 @@ 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 +61,7 @@ export function explode(visitor, mergeConflicts) {
       var existing = visitor[alias];
       if (existing) {
         if (mergeConflicts) {
-          merge(existing, fns);
+          mergePair(existing, fns);
         }
       } else {
         visitor[alias] = fns;
@@ -105,6 +105,19 @@ 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 +148,7 @@ function addSelector(visitor, selector, fns) {
     };
   }
 
-  merge(visitor, fns);
+  mergePair(visitor, fns);
 }
 
 function wrapCheck(wrapper, fn) {
@@ -159,7 +172,7 @@ 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]);
   }
diff --git a/test/core/fixtures/transformation/es6.arrow-functions/arguments/expected.js b/test/core/fixtures/transformation/es6.arrow-functions/arguments/expected.js
index b8104fab4d..2972f6b9b1 100644
--- a/test/core/fixtures/transformation/es6.arrow-functions/arguments/expected.js
+++ b/test/core/fixtures/transformation/es6.arrow-functions/arguments/expected.js
@@ -11,17 +11,17 @@ function one() {
 one(1, 2);
 
 function two() {
-  var _arguments2 = arguments;
+  var _arguments3 = arguments;
 
   var inner = function inner() {
-    return _arguments2;
+    return _arguments3;
   };
 
   var another = function another() {
-    var _arguments3 = arguments;
+    var _arguments2 = arguments;
 
     var inner2 = function inner2() {
-      return _arguments3;
+      return _arguments2;
     };
   };
 
@@ -66,4 +66,4 @@ function six(obj) {
   };
   return fn();
 }
-six();
\ No newline at end of file
+six();
diff --git a/test/core/fixtures/transformation/spec.proto-to-assign/assignment-expression/expected.js b/test/core/fixtures/transformation/spec.proto-to-assign/assignment-expression/expected.js
index 1a55265b4c..0980420528 100644
--- a/test/core/fixtures/transformation/spec.proto-to-assign/assignment-expression/expected.js
+++ b/test/core/fixtures/transformation/spec.proto-to-assign/assignment-expression/expected.js
@@ -1,11 +1,11 @@
 "use strict";
 
-function _defaults(obj, defaults) { var keys = Object.getOwnPropertyNames(defaults); for (var i = 0; i < keys.length; i++) { var key = keys[i]; var value = Object.getOwnPropertyDescriptor(defaults, key); if (value && value.configurable && obj[key] === undefined) { Object.defineProperty(obj, key, value); } } return obj; }
-
 var _foo, _foo$bar, _foo$bar2;
 
+function _defaults(obj, defaults) { var keys = Object.getOwnPropertyNames(defaults); for (var i = 0; i < keys.length; i++) { var key = keys[i]; var value = Object.getOwnPropertyDescriptor(defaults, key); if (value && value.configurable && obj[key] === undefined) { Object.defineProperty(obj, key, value); } } return obj; }
+
 console.log((_foo = foo, _defaults(_foo, bar), _foo));
 
 console.log((_foo$bar = foo[bar], _defaults(_foo$bar, bar), _foo$bar));
 
-console.log((_foo$bar2 = foo[bar()], _defaults(_foo$bar2, bar), _foo$bar2));
\ No newline at end of file
+console.log((_foo$bar2 = foo[bar()], _defaults(_foo$bar2, bar), _foo$bar2));