Require commas between items in a GN list.

tools/gn/parser.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/parser.h"
 
 #include "base/logging.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/operators.h"
 #include "tools/gn/token.h"
@@ skipping 339 matching lines @@
       static_cast<IdentifierNode*>(right.release())));
   return accessor.PassAs<ParseNode>();
 }
 
 // Does not Consume the start or end token.
 scoped_ptr<ListNode> Parser::ParseList(Token::Type stop_before,
                                        bool allow_trailing_comma) {
   scoped_ptr<ListNode> list(new ListNode);
   list->set_begin_token(cur_token());
   bool just_got_comma = false;
+  bool first_time = true;
   while (!LookAhead(stop_before)) {
-    just_got_comma = false;
+    if (!first_time) {
+      if (!just_got_comma) {
+        // Require commas separate things in lists.
+        *err_ = Err(cur_token(), "Expected comma between items.");
+        return scoped_ptr<ListNode>();
+      }
+    }
+    first_time = false;
+
     // Why _OR? We're parsing things that are higher precedence than the ,
     // that separates the items of the list. , should appear lower than
     // boolean expressions (the lowest of which is OR), but above assignments.
     list->append_item(ParseExpression(PRECEDENCE_OR));
     if (has_error())
       return scoped_ptr<ListNode>();
     if (at_end()) {
       *err_ =
           Err(tokens_[tokens_.size() - 1], "Unexpected end of file in list.");
       return scoped_ptr<ListNode>();
@@ skipping 76 matching lines @@
   if (IsAssignment(condition->condition()))
     *err_ = Err(condition->condition(), "Assignment not allowed in 'if'.");
   Consume(Token::RIGHT_PAREN, "Expected ')' after condition of 'if'.");
   condition->set_if_true(ParseBlock().Pass());
   if (Match(Token::ELSE))
     condition->set_if_false(ParseStatement().Pass());
   if (has_error())
     return scoped_ptr<ParseNode>();
   return condition.PassAs<ParseNode>();
 }