further implement the concept of a "Hub" that all traversal paths get access to, also add in some assertions to confirm path state when performing manipulation

src/babel/transformation/file/index.js

@@ -14,6 +14,7 @@ import codeFrame from "../../helpers/code-frame";
 import defaults from "lodash/object/defaults";
 import includes from "lodash/collection/includes";
 import traverse from "../../traversal";
+import Hub from "../../traversal/hub";
 import assign from "lodash/object/assign";
 import Logger from "./logger";
 import parse from "../../helpers/parse";
@@ -44,6 +45,8 @@ export default class File {
     this.ast      = {};
 
     this.buildTransformers();
+
+    this.hub = new Hub(this);
   }
 
   static helpers = [
@@ -467,11 +470,12 @@ export default class File {
 
   _addAst(ast) {
     this.path  = NodePath.get({
+      hub: this.hub,
       parentPath: null,
       parent: ast,
       container: ast,
       key: "program"
-    }).setContext(null, this);
+    }).setContext();
     this.scope = this.path.scope;
     this.ast   = ast;
   }

src/babel/traversal/hub.js

@@ -0,0 +1,5 @@
+export default class Hub {
+  constructor(file) {
+    this.file = file;
+  }
+}

src/babel/traversal/index.js

@@ -54,13 +54,6 @@ function clearNode(node) {
     let key = CLEAR_KEYS[i];
     if (node[key] != null) node[key] = null;
   }
-
-  for (let key in node) {
-    var val = node[key];
-    if (Array.isArray(val)) {
-      delete val._paths;
-    }
-  }
 }
 
 var clearVisitor = {

src/babel/traversal/path/context.js

@@ -1,4 +1,3 @@
-import * as messages from "../../messages";
 import NodePath from "./index";
 import traverse from "../index";
 
@@ -111,11 +110,11 @@ export function stop() {
  * Description
  */
 
-export function setScope(file?) {
+export function setScope() {
   if (this.opts && this.opts.noScope) return;
 
   var target = this.context || this.parentPath;
-  this.scope = NodePath.getScope(this, target && target.scope, file);
+  this.scope = NodePath.getScope(this, target && target.scope, this.hub);
   if (this.scope) this.scope.init();
 }
 
@@ -123,7 +122,7 @@ export function setScope(file?) {
  * Description
  */
 
-export function setContext(context, file) {
+export function setContext(context) {
   this.shouldSkip = false;
   this.shouldStop = false;
   this.removed    = false;
@@ -135,10 +134,7 @@ export function setContext(context, file) {
     this.opts    = context.opts;
   }
 
-  var log = file && this.type === "Program";
-  if (log) file.log.debug("Start scope building");
-  this.setScope(file);
-  if (log) file.log.debug("End scope building");
+  this.setScope();
 
   return this;
 }
@@ -152,11 +148,21 @@ export function setContext(context, file) {
 export function resync() {
   if (this.removed) return;
 
+  this._resyncParent();
   this._resyncContainer();
   this._resyncKey();
+  //this._resyncRemoved();
+}
+
+export function _resyncParent() {
+  if (this.parentPath) {
+    this.parent = this.parentPath.node;
+  }
 }
 
 export function _resyncKey() {
+  if (!this.container) return;
+
   if (this.node === this.container[this.key]) return;
 
   // grrr, path key is out of sync. this is likely due to a modification to the AST
@@ -176,7 +182,7 @@ export function _resyncKey() {
     }
   }
 
-  throw new Error(messages.get("lostTrackNodePath"));
+  this.key = null;
 }
 
 export function _resyncContainer() {
@@ -185,11 +191,21 @@ export function _resyncContainer() {
   if (!containerKey || !parentPath) return;
 
   var newContainer = parentPath.node[containerKey];
-  if (!newContainer || this.container === newContainer) return;
+  if (this.container === newContainer) return;
 
   // container is out of sync. this is likely the result of it being reassigned
 
-  this.container = newContainer;
+  if (newContainer) {
+    this.container = newContainer;
+  } else {
+    this.container = null;
+  }
+}
+
+export function _resyncRemoved() {
+  if (this.key == null || !this.container || this.container[this.key] !== this.node) {
+    this._markRemoved();
+  }
 }
 
 /**
@@ -214,7 +230,10 @@ export function unshiftContext(context) {
  * Description
  */
 
-export function setup(parentPath, key) {
+export function setup(parentPath, container, containerKey, key) {
+  this.containerKey = containerKey;
+  this.container    = container;
+
   this.parentPath = parentPath || this.parentPath;
   this.setKey(key);
 }

src/babel/traversal/path/modification.js

@@ -7,6 +7,8 @@ import * as t from "../../types";
  */
 
 export function insertBefore(nodes) {
+  this._assertUnremoved();
+
   nodes = this._verifyNodeList(nodes);
 
   if (this.parentPath.isExpressionStatement() || this.parentPath.isLabeledStatement()) {
@@ -27,6 +29,7 @@ export function insertBefore(nodes) {
   } else {
     throw new Error("No clue what to do with this node type.");
   }
+
   return [this];
 }
 
@@ -78,6 +81,8 @@ export function _maybePopFromStatements(nodes) {
  */
 
 export function insertAfter(nodes) {
+  this._assertUnremoved();
+
   nodes = this._verifyNodeList(nodes);
 
   if (this.parentPath.isExpressionStatement() || this.parentPath.isLabeledStatement()) {
@@ -102,6 +107,7 @@ export function insertAfter(nodes) {
   } else {
     throw new Error("No clue what to do with this node type.");
   }
+
   return [this];
 }
 
@@ -110,7 +116,7 @@ export function insertAfter(nodes) {
  */
 
 export function updateSiblingKeys(fromIndex, incrementBy) {
-  var paths = this.container._paths;
+  var paths = this.parent._paths;
   for (var i = 0; i < paths.length; i++) {
     let path = paths[i];
     if (path.key >= fromIndex) {
@@ -153,6 +159,8 @@ export function _verifyNodeList(nodes) {
  */
 
 export function unshiftContainer(containerKey, nodes) {
+  this._assertUnremoved();
+
   nodes = this._verifyNodeList(nodes);
 
   // get the first path and insert our nodes before it, if it doesn't exist then it
@@ -175,6 +183,8 @@ export function unshiftContainer(containerKey, nodes) {
  */
 
 export function pushContainer(containerKey, nodes) {
+  this._assertUnremoved();
+
   nodes = this._verifyNodeList(nodes);
 
   // get an invisible path that represents the last node + 1 and replace it with our

src/babel/traversal/path/removal.js

@@ -15,6 +15,8 @@ export function remove() {
  */
 
 export function dangerouslyRemove() {
+  this._assertUnremoved();
+
   this.resync();
 
   if (this._callRemovalHooks("pre")) {
@@ -45,8 +47,15 @@ export function _remove() {
 }
 
 export function _markRemoved() {
-  this.node = null;
-  this.removed = true;
+  this.shouldSkip = true;
+  this.removed    = true;
+  this.node       = null;
+}
+
+export function _assertUnremoved() {
+  if (this.removed) {
+    throw this.errorWithNode("NodePath has been removed so is read-only.");
+  }
 }
 
 /**