LibJS: Plumb line and column information through Lexer / Parser

While debugging test failures, it's pretty frustrating to have to go do
printf debugging to figure out what test is failing right now. While
watching your JS Raytracer stream it seemed like this was pretty
furstrating as well. So I wanted to start working on improving the
diagnostics here.

In the future I hope we can eventually be able to plumb the info down
to the Error classes so any thrown exceptions will contain enough
metadata to know where they came from.

Libraries/LibJS/Lexer.cpp

@@ -39,7 +39,7 @@ HashMap<char, TokenType> Lexer::s_single_char_tokens;
 
 Lexer::Lexer(StringView source)
     : m_source(source)
-    , m_current_token(TokenType::Eof, StringView(nullptr), StringView(nullptr))
+    , m_current_token(TokenType::Eof, StringView(nullptr), StringView(nullptr), 0, 0)
 {
     if (s_keywords.is_empty()) {
         s_keywords.set("await", TokenType::Await);
@@ -146,6 +146,13 @@ void Lexer::consume()
         return;
     }
 
+    if (m_current_char == '\n') {
+        m_line_number++;
+        m_line_column = 1;
+    } else {
+        m_line_column++;
+    }
+
     m_current_char = m_source[m_position++];
 }
 
@@ -182,7 +189,7 @@ bool Lexer::is_block_comment_end() const
 void Lexer::syntax_error(const char* msg)
 {
     m_has_errors = true;
-    fprintf(stderr, "Syntax Error: %s\n", msg);
+    fprintf(stderr, "Syntax Error: %s (line: %zu, column: %zu)\n", msg, m_line_number, m_line_column);
 }
 
 Token Lexer::next()
@@ -317,7 +324,9 @@ Token Lexer::next()
     m_current_token = Token(
         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_source.substring_view(value_start - 1, m_position - value_start),
+        m_line_number,
+        m_line_column);
 
     return m_current_token;
 }

Libraries/LibJS/Lexer.h

@@ -54,8 +54,10 @@ private:
     StringView m_source;
     size_t m_position = 0;
     Token m_current_token;
-    int m_current_char;
+    int m_current_char = 0;
     bool m_has_errors = false;
+    size_t m_line_number = 1;
+    size_t m_line_column = 1;
 
     static HashMap<String, TokenType> s_keywords;
     static HashMap<String, TokenType> s_three_char_tokens;

Libraries/LibJS/Parser.cpp

@@ -967,7 +967,12 @@ Token Parser::consume(TokenType type)
 {
     if (m_parser_state.m_current_token.type() != type) {
         m_parser_state.m_has_errors = true;
-        fprintf(stderr, "Error: Unexpected token %s. Expected %s\n", m_parser_state.m_current_token.name(), Token::name(type));
+        auto& current_token = m_parser_state.m_current_token;
+        fprintf(stderr, "Error: Unexpected token %s. Expected %s (line: %zu, column: %zu))\n",
+                current_token.name(),
+                Token::name(type),
+                current_token.line_number(),
+                current_token.line_column());
     }
     return consume();
 }
@@ -975,7 +980,12 @@ Token Parser::consume(TokenType type)
 void Parser::expected(const char* what)
 {
     m_parser_state.m_has_errors = true;
-    fprintf(stderr, "Error: Unexpected token %s. Expected %s\n", m_parser_state.m_current_token.name(), what);
+    auto& current_token = m_parser_state.m_current_token;
+    fprintf(stderr, "Error: Unexpected token %s. Expected %s (line: %zu, column: %zu)\n",
+            current_token.name(),
+            what,
+            current_token.line_number(),
+            current_token.line_column());
 }
 
 void Parser::save_state()

Libraries/LibJS/Token.h

@@ -131,10 +131,12 @@ enum class TokenType {
 
 class Token {
 public:
-    Token(TokenType type, StringView trivia, StringView value)
+    Token(TokenType type, StringView trivia, StringView value, size_t line_number, size_t line_column)
         : m_type(type)
         , m_trivia(trivia)
         , m_value(value)
+        , m_line_number(line_number)
+        , m_line_column(line_column)
     {
     }
 
@@ -144,6 +146,8 @@ public:
 
     const StringView& trivia() const { return m_trivia; }
     const StringView& value() const { return m_value; }
+    size_t line_number() const { return m_line_number; }
+    size_t line_column() const { return m_line_column; }
     double double_value() const;
     String string_value() const;
     bool bool_value() const;
@@ -152,6 +156,8 @@ private:
     TokenType m_type;
     StringView m_trivia;
     StringView m_value;
+    size_t m_line_number;
+    size_t m_line_column;
 };
 
 }