Fix left recursion detection in sequences

Report left recursion also in cases where the recursive rule invocation
is not a direct element of a sequence, but is wrapped inside an
expression.

Fixes #359.

lib/compiler/passes/report-left-recursion.js

@@ -29,9 +29,7 @@ function reportLeftRecursion(ast) {
 
     sequence: function(node) {
       arrays.every(node.elements, function(element) {
-        if (element.type === "rule_ref") {
-          check(element);
-        }
+        check(element);
 
         return !asts.alwaysAdvancesOnSuccess(ast, element);
       });

spec/unit/compiler/passes/report-left-recursion.spec.js

@@ -39,6 +39,11 @@ describe("compiler pass |reportLeftRecursion|", function() {
       expect(pass).not.toReportError('start = "" "" "a" start');
     });
 
+    /* Regression test for #359. */
+    it("reports left recursion when rule reference is wrapped in an expression", function() {
+      expect(pass).toReportError('start = "" start?');
+    });
+
     it("computes expressions that always advance on success correctly", function() {
       expect(pass).toReportError([
         'start = a start',