[[FIX]] Update parsing of object "rest" property

The latest version of the proposal disallows BindingPattern as the
right-hand side of a "rest" property.

tc39/proposal-object-rest-spread#50
http://tc39.github.io/tc39-notes/2017-05_may-23.html#16ih-why-allow-bindingpattern-for-bindingrestparameter-for-object-rest-maybe-we-should-just-allow-identifiers

Author: jugglinmike

src/jshint.js

@@ -3312,7 +3312,7 @@ var JSHINT = (function() {
 
   (function(x) {
     x.nud = function() {
-      var b, f, i, p, t, isGeneratorMethod = false, nextVal;
+      var b, f, i, p, t, isGeneratorMethod = false, nextVal, expr;
       var props = Object.create(null); // All properties, including accessors
 
       b = state.tokens.curr.line !== startLine(state.tokens.next);
@@ -3502,7 +3502,8 @@ var JSHINT = (function() {
       }
     };
     var assignmentProperty = function() {
-      var id;
+      var id, expr;
+
       if (checkPunctuator(state.tokens.next, "[")) {
         advance("[");
         expression(10);
@@ -3523,7 +3524,16 @@ var JSHINT = (function() {
             warning("W141", state.tokens.next, "object rest property", "objspreadrest");
           }
 
-          nextInnerDE();
+          // Due to visual symmetry with the array rest property (and the early
+          // design of the language feature), developers may mistakenly assume
+          // any expression is valid in this position.  Parse an expression and
+          // issue an error in order to recover more gracefully from this
+          // condition.
+          expr = expression(10);
+
+          if (expr.type !== '(identifier)') {
+            error("E030", expr, expr.value);
+          }
         } else {
           id = identifier();
         }

tests/unit/unstable/objrestspread.js

@@ -79,6 +79,11 @@ exports.rest = function (test) {
   ];
 
   TestRun(test, "nested array pattern, final")
+    .addError(1, "Expected an identifier and instead saw '['.")
+    .addError(2, "Expected an identifier and instead saw '['.")
+    .addError(3, "Expected an identifier and instead saw '['.")
+    .addError(4, "Expected an identifier and instead saw '['.")
+    .addError(5, "Expected an identifier and instead saw '['.")
     .test(code, { esversion: 6, unstable: { objspreadrest: true } });
 
   code = [
@@ -90,19 +95,24 @@ exports.rest = function (test) {
   ];
 
   TestRun(test, "nested array pattern, not final")
+    .addError(1, "Expected an identifier and instead saw '['.")
     .addError(1, "Invalid element after rest element.")
+    .addError(2, "Expected an identifier and instead saw '['.")
     .addError(2, "Invalid element after rest element.")
+    .addError(3, "Expected an identifier and instead saw '['.")
     .addError(3, "Invalid element after rest element.")
+    .addError(4, "Expected an identifier and instead saw '['.")
     .addError(4, "Invalid element after rest element.")
+    .addError(5, "Expected an identifier and instead saw '['.")
     .addError(5, "Invalid element after rest element.")
     .test(code, { esversion: 6, unstable: { objspreadrest: true } });
 
   TestRun(test, "nested array pattern, empty")
-    .addError(1, "Empty destructuring.")
+    .addError(1, "Expected an identifier and instead saw '['.")
     .test("({ ...[] } = {});", { esversion: 6, unstable: { objspreadrest: true } });
 
   TestRun(test, "nested object pattern, empty")
-    .addError(1, "Empty destructuring.")
+    .addError(1, "Expected an identifier and instead saw '{'.")
     .test("({ ...{} } = {});", { esversion: 6, unstable: { objspreadrest: true } });
 
   test.done();