From 2a889535bdd564d75b6e8498839fdb5b57bf26f1 Mon Sep 17 00:00:00 2001
From: David Majda <david@majda.cz>
Date: Mon, 27 Jun 2016 12:27:41 +0200
Subject: [PATCH] Add location to the "Rule ... is already defined" error
 message

See this discussion:

  https://github.com/pegjs/pegjs/commit/eb5875bc6a8ae7454beb6f7057e9d2794fefabc7#commitcomment-17970220
---
 lib/compiler/passes/report-duplicate-rules.js            | 6 ++++--
 spec/unit/compiler/passes/report-duplicate-rules.spec.js | 2 +-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/compiler/passes/report-duplicate-rules.js b/lib/compiler/passes/report-duplicate-rules.js
index 44cfa27..c621d37 100644
--- a/lib/compiler/passes/report-duplicate-rules.js
+++ b/lib/compiler/passes/report-duplicate-rules.js
@@ -11,12 +11,14 @@ function reportDuplicateRules(ast) {
     rule: function(node) {
       if (rules.hasOwnProperty(node.name)) {
         throw new GrammarError(
-          "Rule \"" + node.name + "\" is already defined.",
+          "Rule \"" + node.name + "\" is already defined "
+            + "at line " + rules[node.name].start.line + ", "
+            + "column " + rules[node.name].start.column + ".",
           node.location
         );
       }
 
-      rules[node.name] = true;
+      rules[node.name] = node.location;
     }
   });
 
diff --git a/spec/unit/compiler/passes/report-duplicate-rules.spec.js b/spec/unit/compiler/passes/report-duplicate-rules.spec.js
index a74554e..19641eb 100644
--- a/spec/unit/compiler/passes/report-duplicate-rules.spec.js
+++ b/spec/unit/compiler/passes/report-duplicate-rules.spec.js
@@ -10,7 +10,7 @@ describe("compiler pass |reportDuplicateRules|", function() {
       'start = "a"',
       'start = "b"'
     ].join('\n'), {
-      message:  'Rule "start" is already defined.',
+      message:  'Rule "start" is already defined at line 1, column 1.',
       location: {
         start: { offset: 12, line: 2, column:  1 },
         end:   { offset: 23, line: 2, column: 12 }