Add nocomma option to forbid use of a comma operator

src/jshint.js

@@ -92,6 +92,7 @@ var JSHINT = (function () {
         // statements inside of a one-line blocks.
         newcap      : true, // if constructor names must be capitalized
         noarg       : true, // if arguments.caller and arguments.callee should be
+        nocomma     : true, // if comma operator should be disallowed
         noempty     : true, // if empty blocks should be disallowed
         nonbsp      : true, // if non-breaking spaces should be disallowed
         nonew       : true, // if using `new` for side-effects should be disallowed
@@ -2237,6 +2238,10 @@ var JSHINT = (function () {
   bitwiseassignop(">>=");
   bitwiseassignop(">>>=");
   infix(",", function (left, that) {
+    if (state.option.nocomma) {
+      warning("W127");
+    }
+
     var expr;
     that.exprs = [left];
     if (!comma({peek: true})) {

src/messages.js

@@ -200,7 +200,8 @@ var warnings = {
   W123: "'{a}' is already defined in outer scope.",
   W124: "A generator function shall contain a yield statement.",
   W125: "This line contains non-breaking spaces: http://jshint.com/doc/options/#nonbsp",
-  W126: "Grouping operator is unnecessary for lone expressions."
+  W126: "Grouping operator is unnecessary for lone expressions.",
+  W127: "Unexpected use of a comma operator."
 };
 
 var info = {

tests/unit/options.js

@@ -1626,6 +1626,19 @@ exports.nonbsp = function (test) {
   test.done();
 };
 
+/** Option `nocomma` disallows the use of comma operator. */
+exports.nocomma = function (test) {
+  // By default allow comma operator
+  TestRun(test)
+    .test('return 2, 5;', {});
+
+  TestRun(test)
+    .addError(1, "Unexpected use of a comma operator.")
+    .test('return 2, 5;', { nocomma: true });
+
+  test.done();
+};
+
 exports.enforceall = function (test) {
   var src = fs.readFileSync(__dirname + "/fixtures/enforceall.js", "utf8");