add validation.react transformer

lib/6to5/messages.js

@@ -15,7 +15,8 @@ exports.messages = {
   invalidParentForThisNode: "We don't know how to handle this node within the current parent - please open an issue",
   readOnly: "$1 is read-only",
   modulesIllegalExportName: "Illegal export $1",
-  unknownForHead: "Unknown node type $1 in ForStatement"
+  unknownForHead: "Unknown node type $1 in ForStatement",
+  didYouMean: "Did you mean $1?"
 };
 
 exports.get = function (key) {

lib/6to5/transformation/transformers/index.js

@@ -4,6 +4,7 @@ module.exports = {
   "validation.undeclaredVariableCheck":    require("./validation/undeclared-variable-check"),
   "validation.noForInOfAssignment":        require("./validation/no-for-in-of-assignment"),
   "validation.setters":                    require("./validation/setters"),
+  "validation.react":                      require("./validation/react"),
   "spec.blockScopedFunctions":             require("./spec/block-scoped-functions"),
 
   "playground.malletOperator":             require("./playground/mallet-operator"),

lib/6to5/transformation/transformers/validation/react.js

@@ -0,0 +1,25 @@
+var messages = require("../../../messages");
+var t        = require("../../../types");
+
+// check if the input Literal `source` is an alternate casing of "react"
+var check = function (source, file) {
+  if (t.isLiteral(source)) {
+    var name  = source.value;
+    var lower = name.toLowerCase();
+
+    if (lower === "react" && name !== lower) {
+      throw file.errorWithNode(source, messages.get("didYouMean", "react"));
+    }
+  }
+};
+
+exports.CallExpression = function (node, parent, scope, file) {
+  if (t.isIdentifier(node.callee, { name: "require" }) && node.arguments.length === 1) {
+    check(node.arguments[0], file);
+  }
+};
+
+exports.ImportDeclaration =
+exports.ExportDeclaration = function (node, parent, scope, file) {
+  check(node.source, file);
+};