add Flow virtual type

packages/babel/src/traversal/path/index.js

@@ -145,8 +145,7 @@ for (let type of (t.TYPES: Array)) {
 
 for (let type in virtualTypes) {
   if (type[0] === "_") continue;
-
-  t.TYPES.push(type);
+  if (t.TYPES.indexOf(type) < 0) t.TYPES.push(type);
 
   NodePath.prototype[`is${type}`] = function (opts) {
     return virtualTypes[type].checkPath(this, opts);

packages/babel/src/traversal/path/lib/virtual-types.js

@@ -110,6 +110,10 @@ export var Var = {
   }
 };
 
+/**
+ * [Please add a description.]
+ */
+
 export var DirectiveLiteral = {
   types: ["Literal"],
   checkPath(path) {
@@ -117,6 +121,10 @@ export var DirectiveLiteral = {
   }
 };
 
+/**
+ * [Please add a description.]
+ */
+
 export var Directive = {
   types: ["ExpressionStatement"],
   checkPath(path) {
@@ -124,14 +132,39 @@ export var Directive = {
   }
 };
 
+/**
+ * [Please add a description.]
+ */
+
 export var User = {
   checkPath(path) {
     return path.node && !!path.node.loc;
   }
 };
 
+/**
+ * [Please add a description.]
+ */
+
 export var Generated = {
   checkPath(path) {
     return !path.isUser();
   }
 };
+
+/**
+ * [Please add a description.]
+ */
+
+export var Flow = {
+  types: ["Flow", "ImportDeclaration"],
+  checkPath({ node }) {
+    if (t.isFlow(node)) {
+      return true;
+    } else if (t.isImportDeclaration(node)) {
+      return node.importKind === "type" || node.importKind === "typeof";
+    } else {
+      return false;
+    }
+  }
+};

packages/babel/src/traversal/visitors.js

@@ -40,7 +40,7 @@ export function explode(visitor) {
   ensureCallbackArrays(visitor);
 
   // add type wrappers
-  for (let nodeType in visitor) {
+  for (let nodeType of (Object.keys(visitor): Array)) {
     if (shouldIgnoreKey(nodeType)) continue;
 
     var wrapper = virtualTypes[nodeType];