add validation to plugins

src/babel/messages.js

@@ -37,7 +37,17 @@ export const MESSAGES = {
   pluginNotTransformer: "The plugin $1 didn't export a Plugin instance",
   pluginUnknown: "Unknown plugin $1",
 
-  pluginNotFile: "Plugin $1 is resolving to a different Babel version than what is performing the transformation."
+  pluginNotFile: "Plugin $1 is resolving to a different Babel version than what is performing the transformation.",
+
+  pluginInvalidProperty: "Plugin $1 provided an invalid property of $2.",
+  pluginInvalidPropertyVisitor: `Define your visitor methods inside a \`visitor\` property like so:
+
+  new Plugin("foobar", {
+    visitor: {
+      // define your visitor methods here!
+    }
+  });
+`
 };
 
 export function get(key: String, ...args) {

src/babel/transformation/plugin.js

@@ -1,13 +1,30 @@
 import PluginPass from "./plugin-pass";
 import * as messages from "../messages";
-import isFunction from "lodash/lang/isFunction";
 import traverse from "../traversal";
 import assign from "lodash/object/assign";
 import clone from "lodash/lang/clone";
 import File from "./file";
+import * as t from "../types";
+
+const VALID_PLUGIN_PROPERTIES = [
+  "visitor", "metadata",
+  "manipulateOptions",
+  "post", "pre"
+];
+
+const VALID_METADATA_PROPERTES = [
+  "dependencies",
+  "optional",
+  "stage",
+  "group",
+  "experimental",
+  "secondPass"
+];
 
 export default class Plugin {
   constructor(key: string, plugin: Object) {
+    Plugin.validate(key, plugin);
+
     plugin = assign({}, plugin);
 
     var take = function (key) {
@@ -34,13 +51,25 @@ export default class Plugin {
     this.key     = key;
   }
 
-  normalize(visitor: Object): Object {
-    if (isFunction(visitor)) {
-      visitor = { ast: visitor };
+  static validate(name, plugin) {
+    for (let key in plugin) {
+      if (key[0] === "_") continue;
+      if (VALID_PLUGIN_PROPERTIES.indexOf(key) >= 0) continue;
+
+      var msgType = "pluginInvalidProperty";
+      if (t.TYPES.indexOf(key) >= 0) msgType = "pluginInvalidPropertyVisitor";
+      throw new Error(messages.get(msgType, name, key));
     }
 
-    traverse.explode(visitor);
+    for (let key in plugin.metadata) {
+      if (VALID_METADATA_PROPERTES.indexOf(key) >= 0) continue;
 
+      throw new Error(messages.get("pluginInvalidProperty", name, `metadata.${key}`));
+    }
+  }
+
+  normalize(visitor: Object): Object {
+    traverse.explode(visitor);
     return visitor;
   }
 

src/babel/traversal/path/index.js

@@ -123,17 +123,19 @@ assign(NodePath.prototype, require("./modification"));
 assign(NodePath.prototype, require("./family"));
 assign(NodePath.prototype, require("./comments"));
 
-for (let type in virtualTypes) {
-  if (type[0] === "_") continue;
-
-  NodePath.prototype[`is${type}`] = function (opts) {
-    return virtualTypes[type].checkPath(this, opts);
-  };
-}
-
 for (let type of (t.TYPES: Array)) {
   let typeKey = `is${type}`;
   NodePath.prototype[typeKey] = function (opts) {
     return t[typeKey](this.node, opts);
   };
 }
+
+for (let type in virtualTypes) {
+  if (type[0] === "_") continue;
+
+  t.TYPES.push(type);
+
+  NodePath.prototype[`is${type}`] = function (opts) {
+    return virtualTypes[type].checkPath(this, opts);
+  };
+}

src/babel/traversal/visitors.js

@@ -106,7 +106,7 @@ export function verify(visitor) {
   for (var nodeType in visitor) {
     if (shouldIgnoreKey(nodeType)) continue;
 
-    if (t.TYPES.indexOf(nodeType) < 0 && !virtualTypes[nodeType]) {
+    if (t.TYPES.indexOf(nodeType) < 0) {
       throw new Error(messages.get("traverseVerifyNodeType", nodeType));
     }