ResumableParser: Don't compute lines and columns on parse error

Fix: #1022

They can't always be accurate because we don't always keep the
full document in the buffer. As such it's better never to compute
them than to sometimes provide wrong coordinates.

In theory we could keep the number of lines since the start
of the parse, but that's more book keeping for little utility.

Anyway, these are useful to find a syntax error in a file,
not so much in a stream of documents.

Author: byroot

ext/json/ext/parser/parser.c

@@ -627,7 +627,7 @@ static void emit_parse_warning(const char *message, JSON_ParserState *state)
 
 #define PARSE_ERROR_FRAGMENT_LEN 32
 
-static VALUE build_parse_error_message(const char *format, JSON_ParserState *state, long line, long column)
+static VALUE build_parse_error_message(const char *format, JSON_ParserState *state)
 {
     unsigned char buffer[PARSE_ERROR_FRAGMENT_LEN + 3];
 
@@ -661,9 +661,7 @@ static VALUE build_parse_error_message(const char *format, JSON_ParserState *sta
         }
     }
 
-    VALUE message = rb_enc_sprintf(enc_utf8, format, ptr);
-    rb_str_catf(message, " at line %ld column %ld", line, column);
-    return message;
+    return rb_enc_sprintf(enc_utf8, format, ptr);
 }
 
 static VALUE parse_error_new(JSON_ParserState *state, VALUE message, long line, long column, bool eos)
@@ -679,10 +677,15 @@ static VALUE parse_error_new(JSON_ParserState *state, VALUE message, long line,
 
 NORETURN(static) void raise_parse_error(const char *format, JSON_ParserState *state, bool eos)
 {
-    long line, column;
-    cursor_position(state, &line, &column);
-    VALUE message = build_parse_error_message(format, state, line, column);
-    rb_exc_raise(parse_error_new(state, message, line, column, eos));
+    VALUE message = build_parse_error_message(format, state);
+    if (state->parser) { // line and columns can't be accurate in resumable
+        rb_exc_raise(parse_error_new(state, message, 0, 0, eos));
+    } else {
+        long line, column;
+        cursor_position(state, &line, &column);
+        rb_str_catf(message, " at line %ld column %ld", line, column);
+        rb_exc_raise(parse_error_new(state, message, line, column, eos));
+    }
 }
 
 NORETURN(static) void raise_eos_error(const char *format, JSON_ParserState *state)
@@ -1172,10 +1175,15 @@ NORETURN(static) void raise_duplicate_key_error(JSON_ParserState *state, VALUE d
         rb_inspect(duplicate_key)
     );
 
-    long line, column;
-    cursor_position(state, &line, &column);
-    rb_str_concat(message, build_parse_error_message("", state, line, column)) ;
-    rb_exc_raise(parse_error_new(state, message, line, column, false));
+    rb_str_concat(message, build_parse_error_message("", state));
+    if (state->parser) { // line and columns can't be accurate in resumable
+        rb_exc_raise(parse_error_new(state, message, 0, 0, false));
+    } else {
+        long line, column;
+        cursor_position(state, &line, &column);
+        rb_str_catf(message, " at line %ld column %ld", line, column);
+        rb_exc_raise(parse_error_new(state, message, line, column, false));
+    }
 }
 
 NOINLINE(static) void json_on_duplicate_key(JSON_ParserState *state, JSON_ParserConfig *config, size_t count, const VALUE *pairs)

test/json/resumable_parser_test.rb

@@ -384,14 +384,24 @@ def test_parsed_bytes
     assert_equal 0, @parser.parsed_bytes
   end
 
+  def test_parse_error_message
+    error = assert_parse_error("\n\n[plop\nfoo", "unexpected character: 'plop'")
+    assert_equal 0, error.line
+    assert_equal 0, error.column
+  end
+
   private
 
-  def assert_parse_error(json)
+  def assert_parse_error(json, expected_error_message = nil)
     parser = new_parser
     parser << json
-    assert_raise(JSON::ParserError, "expected a parse error for #{json.inspect}") do
+    error = assert_raise(JSON::ParserError, "expected a parse error for #{json.inspect}") do
       parser.parse
     end
+    if expected_error_message
+      assert_equal expected_error_message, error.message
+    end
+    error
   end
 
   def assert_incomplete(json)