Add static errors for object rest (#149)

* Fix parsing object rest

This makes object-rest-spread behave according to spec and only
allow one rest operator and enforces it to be the last
param in the object.

Also move all object-rest-spread tests to a own folder.

* Show nicer error messages

src/parser/expression.js

@@ -691,6 +691,8 @@ pp.parseObj = function (isPattern, refShorthandDefaultPos) {
   node.properties = [];
   this.next();
 
+  let firstRestLocation = null;
+
   while (!this.eat(tt.braceR)) {
     if (first) {
       first = false;
@@ -713,7 +715,21 @@ pp.parseObj = function (isPattern, refShorthandDefaultPos) {
       prop = this.parseSpread();
       prop.type = isPattern ? "RestProperty" : "SpreadProperty";
       node.properties.push(prop);
-      continue;
+      if (isPattern) {
+        const position = this.state.start;
+        if (firstRestLocation !== null) {
+          this.unexpected(firstRestLocation, "Cannot have multiple rest elements when destructuring");
+        } else if (this.eat(tt.braceR)) {
+          break;
+        } else if (this.match(tt.comma) && this.lookahead().type === tt.braceR) {
+          this.unexpected(position, "A trailing comma is not permitted after the rest element");
+        } else {
+          firstRestLocation = position;
+          continue;
+        }
+      } else {
+        continue;
+      }
     }
 
     prop.method = false;
@@ -753,6 +769,10 @@ pp.parseObj = function (isPattern, refShorthandDefaultPos) {
     node.properties.push(prop);
   }
 
+  if (firstRestLocation !== null) {
+    this.unexpected(firstRestLocation, "The rest element has to be the last element when destructuring");
+  }
+
   if (decorators.length) {
     this.raise(this.state.start, "You have trailing decorators with no property");
   }