Fix too eager proxy rules removal

Fixes GH-137.

lib/compiler/passes/remove-proxy-rules.js

@@ -3,7 +3,7 @@ var utils = require("../../utils");
 /*
  * Removes proxy rules -- that is, rules that only delegate to other rule.
  */
-module.exports = function(ast) {
+module.exports = function(ast, options) {
   function isProxyRule(node) {
     return node.type === "rule" && node.expression.type === "rule_ref";
   }
@@ -55,15 +55,17 @@ module.exports = function(ast) {
     replace(ast, from, to);
   }
 
-  var indices = [];
+  var indices = [],
+      allowedStartRules = options.allowedStartRules !== undefined
+        ? options.allowedStartRules
+        : [ast.startRule];
 
   utils.each(ast.rules, function(rule, i) {
     if (isProxyRule(rule)) {
       replaceRuleRefs(ast, rule.name, rule.expression.name);
-      if (rule.name === ast.startRule) {
-        ast.startRule = rule.expression.name;
+      if (!utils.contains(allowedStartRules, rule.name)) {
+        indices.push(i);
       }
-      indices.push(i);
     }
   });
 

spec/compiler/passes/remove-proxy-rules.spec.js

@@ -19,8 +19,8 @@ describe("compiler pass |removeProxyRules|", function() {
 
   it("removes proxy rule from a rule", function() {
     expect(pass).toChangeAST(proxyGrammar('start = proxy'), {
-      startRule: "proxied",
-      rules:     [
+      rules: [
+        { type: "rule", name: "start", expression: proxiedRefDetails },
         { type: "rule", name: "proxied" }
       ]
     });
@@ -86,4 +86,17 @@ describe("compiler pass |removeProxyRules|", function() {
   it("removes proxy rule from a one or more", function() {
     expect(pass).toChangeAST(proxyGrammar('start = proxy+'), simpleDetails);
   });
+
+  it("doesn't remove a proxy rule listed in |allowedStartRules|", function() {
+    expect(pass).toChangeAST(
+      proxyGrammar('start = proxy'),
+      { allowedStartRules: ["proxy"] },
+      {
+        rules: [
+          { name: "proxy"   },
+          { name: "proxied" }
+        ]
+      }
+    );
+  });
 });

spec/helpers.js

@@ -4,7 +4,7 @@ if (typeof module !== "undefined") {
 
 beforeEach(function() {
   this.addMatchers({
-    toChangeAST: function(grammar, details) {
+    toChangeAST: function(grammar) {
       function matchDetails(value, details) {
         function isArray(value) {
           return Object.prototype.toString.apply(value) === "[object Array]";
@@ -40,12 +40,15 @@ beforeEach(function() {
         }
       }
 
-      var ast = PEG.parser.parse(grammar);
+      var options = arguments.length > 2 ? arguments[1] : {},
+          details = arguments[arguments.length - 1],
+          ast     = PEG.parser.parse(grammar);
 
-      this.actual(ast);
+      this.actual(ast, options);
 
       this.message = function() {
         return "Expected the pass "
+             + "with options " + jasmine.pp(options) + " "
              + (this.isNot ? "not " : "")
              + "to change the AST " + jasmine.pp(ast) + " "
              + "to match " + jasmine.pp(details) + ", "