LibJS: Fix start position of multi-line tokens

This broke in case of unterminated regular expressions, causing goofy location
numbers, and 'source_location_hint' to eat up all memory:

Unexpected token UnterminatedRegexLiteral. Expected statement (line: 2, column: 4294967292)

Libraries/LibJS/Lexer.cpp

@@ -248,17 +248,17 @@ bool Lexer::slash_means_division() const
 {
  auto type = m_current_token.type();
  return type == TokenType::BigIntLiteral
-  || type == TokenType::BoolLiteral
-  || type == TokenType::BracketClose
-  || type == TokenType::CurlyClose
-  || type == TokenType::Identifier
-  || type == TokenType::NullLiteral
-  || type == TokenType::NumericLiteral
-  || type == TokenType::ParenClose
-  || type == TokenType::RegexLiteral
-  || type == TokenType::StringLiteral
-  || type == TokenType::TemplateLiteralEnd
-  || type == TokenType::This;
+ || type == TokenType::BoolLiteral
+ || type == TokenType::BracketClose
+ || type == TokenType::CurlyClose
+ || type == TokenType::Identifier
+ || type == TokenType::NullLiteral
+ || type == TokenType::NumericLiteral
+ || type == TokenType::ParenClose
+ || type == TokenType::RegexLiteral
+ || type == TokenType::StringLiteral
+ || type == TokenType::TemplateLiteralEnd
+ || type == TokenType::This;
 }
 
 Token Lexer::next()
@@ -292,6 +292,8 @@ Token Lexer::next()
  }
 
  size_t value_start = m_position;
+ size_t value_start_line_number = m_line_number;
+ size_t value_start_column_number = m_line_column;
  auto token_type = TokenType::Invalid;
 
  if (m_current_token.type() == TokenType::RegexLiteral && !is_eof() && isalpha(m_current_char)) {
@@ -511,8 +513,8 @@ Token Lexer::next()
  token_type,
  m_source.substring_view(trivia_start - 1, value_start - trivia_start),
  m_source.substring_view(value_start - 1, m_position - value_start),
- m_line_number,
- m_line_column - m_position + value_start);
+ value_start_line_number,
+ value_start_column_number);
 
  return m_current_token;
 }

Meta/Lagom/Fuzzers/FuzzJs.cpp

@@ -36,7 +36,13 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
  auto lexer = JS::Lexer(js);
  auto parser = JS::Parser(lexer);
  parser.parse_program();
- if (parser.has_errors())
- parser.print_errors();
+ if (parser.has_errors()) {
+ for (auto& error : parser.errors()) {
+ if (error.line >= 100000 || error.column >= 100000) {
+ fprintf(stderr, "%s\n", error.to_string().characters());
+ ASSERT_NOT_REACHED();
+ }
+ }
+ }
  return 0;
 }