fix: lexer out of bounds

example.ll

@@ -1,7 +0,0 @@
-label main:
-b0:
-  %1 = mul i32 3, i32 3
-  %2 = add %1, i32 1
-  param %2
-  %3 = call putchar
-

example.rx

@@ -1,3 +1,18 @@
+extern putchar
+
+fn hello() {
+    local h = 72
+    putchar(h)
+    local e = h - 3
+    putchar(e)
+    local l = h + 4
+    putchar(l)
+    putchar(l)
+    local o = 100 - 21
+    putchar(o)
+}
+
 fn main() {
+    hello()
     putchar(3 * 3 + 1)
 }

include/parser/lexer.hpp

@@ -92,72 +92,98 @@ public:
 public:
     bool NextToken()
     {
-        if (m_pos > m_code.len())
+        auto len = m_code.len();
+
+        auto peek = [&]() -> char {
+            return (m_pos < len) ? m_code.data[m_pos] : '\0';
+        };
+
+        auto advance = [&]() -> char {
+            return (m_pos < len) ? m_code.data[m_pos++] : '\0';
+        };
+
+        // IMPORTANT: >= not >
+        if (m_pos >= len)
         {
             m_token = Token(TokenType::Eof);
             return false;
         }
 
-        char c = m_code.data[m_pos++];
+        char c = advance();
 
-        while(std::isspace(c)) {
+        // skip whitespace safely
+        while (c != '\0' && std::isspace((unsigned char)c))
+        {
             if (c == '\n')
             {
                 m_line++;
                 m_last_newline = m_pos;
             }
-            c = m_code.data[m_pos++];
+
+            if (m_pos >= len) // reached real EOF while skipping whitespace
+            {
+                m_token = Token(TokenType::Eof);
+                return false;
+            }
+
+            c = advance();
         }
 
-        if (m_pos-1 > m_code.len())
+        if (c == '\0' || m_pos > len) // paranoia guard
         {
             m_token = Token(TokenType::Eof);
             return false;
         }
 
-        if (std::isalpha(c) != 0 || c == '_')
+        // identifier
+        if (std::isalpha((unsigned char)c) || c == '_')
         {
             StringBuilder s;
-            long offset_start = m_pos - m_last_newline;
+            long offset_start = m_pos - m_last_newline - 1; // -1 because we already consumed c
             s.Push(c);
-            // id
+
-            while (std::isalpha(m_code.data[m_pos]) != 0 || m_code.data[m_pos] == '_')
+            // NOTE: usually identifiers allow digits after first char; add isdigit if you want
+            while (true)
             {
-                s.Push(m_code.data[m_pos++]);
+                char p = peek();
+                if (!(std::isalpha((unsigned char)p) || p == '_'))
+                    break;
+                s.Push(advance());
             }
+
             s.Push('\0');
-            m_token = Token(TokenType::Id, m_line, offset_start, offset_start);
+            m_token = Token(TokenType::Id, m_line, offset_start, m_pos - m_last_newline);
             m_token.string = s.view();
 
-            if (strcmp("extern", m_token.string.c_str()) == 0)
+            if (strcmp("extern", m_token.string.c_str()) == 0) m_token.token = TokenType::Extern;
-            {
+            else if (strcmp("fn", m_token.string.c_str()) == 0) m_token.token = TokenType::Fn;
-                m_token.token = TokenType::Extern;
+            else if (strcmp("local", m_token.string.c_str()) == 0) m_token.token = TokenType::Local;
-            }
-
-            if (strcmp("fn", m_token.string.c_str()) == 0)
-            {
-                m_token.token = TokenType::Fn;
-            }
-
-            if (strcmp("local", m_token.string.c_str()) == 0)
-            {
-                m_token.token = TokenType::Local;
-            }
 
             return true;
         }
 
-        if (std::isdigit(c) != 0)
+        // integer (hex supported)
+        if (std::isdigit((unsigned char)c))
         {
             StringBuilder s;
-            long offset_start = m_pos - m_last_newline;
+            long offset_start = m_pos - m_last_newline - 1;
-            bool hex = c == '0' && m_code.data[m_pos] == 'x';
+
+            bool hex = (c == '0' && peek() == 'x');
             s.Push(c);
-            // integer (could be hex)
+
-            while (std::isdigit(m_code.data[m_pos]) != 0 || (hex && std::isalpha(m_code.data[m_pos]) != 0))
+            if (hex) s.Push(advance()); // consume 'x'
+
+            while (true)
             {
-                s.Push(m_code.data[m_pos++]);
+                char p = peek();
+                if (std::isdigit((unsigned char)p) ||
+                    (hex && std::isxdigit((unsigned char)p)))
+                {
+                    s.Push(advance());
+                }
+                else break;
             }
+
             s.Push('\0');
             m_token = Token(TokenType::IntLiteral, m_line, offset_start, m_pos - m_last_newline);
             m_token.int_number = std::strtol(s.data, nullptr, hex ? 16 : 10);
@@ -165,7 +191,8 @@ public:
             return true;
         }
 
-        m_token = Token((TokenType)c, m_line, m_pos - m_last_newline, m_pos - m_last_newline + 1);
+        // single-char token fallback
+        m_token = Token((TokenType)c, m_line, m_pos - m_last_newline - 1, m_pos - m_last_newline);
         return true;
     }