From 40120bce701e1cb45f2ad637ec37d976e0c4b979 Mon Sep 17 00:00:00 2001
From: John Hawthorn <john@hawthorn.email>
Date: Mon, 19 Sep 2022 17:56:19 -0700
Subject: [PATCH] Fix "unexpected token" offset for Infinity

Previously in the JSON::Ext parser, when we encountered an "Infinity"
token (and weren't allowing NaN/Infinity) we would try to display the
"unexpected token" at the character before.
---
 ext/json/ext/parser/parser.c  |  2 +-
 ext/json/ext/parser/parser.rl |  2 +-
 tests/json_ext_parser_test.rb | 17 +++++++++++++++++
 3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/ext/json/ext/parser/parser.c b/ext/json/ext/parser/parser.c
index 9bd7f1971..71f59f095 100644
--- a/ext/json/ext/parser/parser.c
+++ b/ext/json/ext/parser/parser.c
@@ -990,7 +990,7 @@ static char *JSON_parse_value(JSON_Parser *json, char *p, char *pe, VALUE *resul
 			if (json->allow_nan) {
 				*result = CInfinity;
 			} else {
-				rb_enc_raise(EXC_ENCODING eParserError, "unexpected token at '%s'", p - 8);
+				rb_enc_raise(EXC_ENCODING eParserError, "unexpected token at '%s'", p - 7);
 			}
 		}
 
diff --git a/ext/json/ext/parser/parser.rl b/ext/json/ext/parser/parser.rl
index 2dbdc7ef2..aafafc153 100644
--- a/ext/json/ext/parser/parser.rl
+++ b/ext/json/ext/parser/parser.rl
@@ -229,7 +229,7 @@ static char *JSON_parse_object(JSON_Parser *json, char *p, char *pe, VALUE *resu
         if (json->allow_nan) {
             *result = CInfinity;
         } else {
-            rb_enc_raise(EXC_ENCODING eParserError, "unexpected token at '%s'", p - 8);
+            rb_enc_raise(EXC_ENCODING eParserError, "unexpected token at '%s'", p - 7);
         }
     }
     action parse_string {
diff --git a/tests/json_ext_parser_test.rb b/tests/json_ext_parser_test.rb
index c5a030ea8..9815c41a3 100644
--- a/tests/json_ext_parser_test.rb
+++ b/tests/json_ext_parser_test.rb
@@ -3,6 +3,8 @@
 
 class JSONExtParserTest < Test::Unit::TestCase
   if defined?(JSON::Ext::Parser)
+    include JSON
+
     def test_allocate
       parser = JSON::Ext::Parser.new("{}")
       assert_raise(TypeError, '[ruby-core:35079]') do
@@ -11,5 +13,20 @@ def test_allocate
       parser = JSON::Ext::Parser.allocate
       assert_raise(TypeError, '[ruby-core:35079]') { parser.source }
     end
+
+    def test_error_messages
+      ex = assert_raise(ParserError) { parse('Infinity') }
+      assert_equal "unexpected token at 'Infinity'", ex.message
+
+      ex = assert_raise(ParserError) { parse('-Infinity') }
+      assert_equal "unexpected token at 'Infinity'", ex.message
+
+      ex = assert_raise(ParserError) { parse('NaN') }
+      assert_equal "unexpected token at 'NaN'", ex.message
+    end
+
+    def parse(json)
+      JSON::Ext::Parser.new(json).parse
+    end
   end
 end