Fix parser error positions for newlines and multibyte characters

Author: ydah

ext/json/ext/parser/parser.c

@@ -592,19 +592,15 @@ static void cursor_position(JSON_ParserState *state, long *line_out, long *colum
     }
 
     const char *cursor = state->cursor;
-    long column = 0;
     long line = 1;
 
-    while (cursor >= state->start) {
-        if (*cursor-- == '\n') {
-            line++;
-            break;
-        }
-        column++;
+    while (cursor > state->start && cursor[-1] != '\n') {
+        cursor--;
     }
+    long column = rb_enc_strlen(cursor, state->cursor, enc_utf8) + 1;
 
-    while (cursor >= state->start) {
-        if (*cursor-- == '\n') {
+    while (cursor > state->start) {
+        if (*--cursor == '\n') {
             line++;
         }
     }

java/src/json/ext/Parser.java

@@ -138,7 +138,7 @@ class ParserError < JSONError
     # Is +nil+ when raised by JSON::ResumableParser.
     attr_reader :line
 
-    # Column number where the parser encountered an error.
+    # One-based column number where the parser encountered an error, counted in Unicode codepoints.
     # Is +nil+ when raised by JSON::ResumableParser.
     attr_reader :column
 

lib/json/common.rb

@@ -935,6 +935,33 @@ def test_parse_error_position
     assert_equal 17, error.column
   end
 
+  def test_parse_error_position_at_newline
+    omit "JRuby string decoding errors don't contain positions" if RUBY_ENGINE == "jruby"
+
+    ["[1,\n\"ab\ncd\"]", "[1,\n\"日本\ncd\"]"].each do |json|
+      error = assert_raise(JSON::ParserError) { JSON.parse(json) }
+      assert_equal 2, error.line
+      assert_equal 4, error.column
+      assert_include error.message, 'at line 2 column 4'
+    end
+  end
+
+  def test_parse_error_position_with_multibyte_characters
+    {
+      '["日本", @]' => [1, 8],
+      "[\n\"é日😀\", @" => [2, 8],
+      '{"日本":{"a":1,"a":2}}' => [1, 7],
+      '["日本",' => [1, 7],
+      "[1,\n" => [2, 1],
+      '' => [1, 1],
+    }.each do |json, (line, column)|
+      error = assert_raise(JSON::ParserError) { JSON.parse(json) }
+      assert_equal line, error.line
+      assert_equal column, error.column
+      assert_include error.message, "at line #{line} column #{column}"
+    end
+  end
+
   def test_parse_error_json_path_on_load
     assert_parse_error_at "$" do
       JSON.load('{"a": {"b": {"c":', -> (obj) {