make it illegal to have a rest on a setter

src/babel/messages.js

@@ -10,6 +10,7 @@ export var messages = {
   undeclaredVariable: "Reference to undeclared variable $1",
   undeclaredVariableSuggestion: "Reference to undeclared variable $1 - did you mean $2?",
   settersInvalidParamLength: "Setters must have exactly one parameter",
+  settersNoRest: "Setters aren't allowed to have a rest",
   noAssignmentsInForHead: "No assignments allowed in for-in/of head",
   expectedMemberExpressionOrIdentifier: "Expected type MemeberExpression or Identifier",
   invalidParentForThisNode: "We don't know how to handle this node within the current parent - please open an issue",

src/babel/transformation/transformers/index.js

@@ -3,6 +3,7 @@ export default {
 
   _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

src/babel/transformation/transformers/internal/validation.js

@@ -12,8 +12,15 @@ export function ForOfStatement(node, parent, scope, file) {
 export { ForOfStatement as ForInStatement };
 
 export function Property(node, parent, scope, file) {
-  if (node.kind === "set" && node.value.params.length !== 1) {
-    throw file.errorWithNode(node.value, messages.get("settersInvalidParamLength"));
+  if (node.kind === "set") {
+    if (node.value.params.length !== 1) {
+      throw file.errorWithNode(node.value, messages.get("settersInvalidParamLength"));
+    }
+
+    var first = node.value.params[0];
+    if (t.isRestElement(first)) {
+      throw file.errorWithNode(first, messages.get("settersNoRest"));
+    }
   }
 }