nodejs/node · error

Illegal code point U+%X\n

Error message

Illegal code point U+%X\n

What it means

Emitted by parseHex() in escapesrc after it decodes a \UXXXXXXXX escape and masks it to 21 bits (c & 0x1FFFFF). U8_LENGTH(ch) returns 0 only for code points beyond U+10FFFF, which cannot be encoded in UTF-8. The tool rejects such code points because it cannot emit a valid UTF-8 byte sequence for them.

Source

Thrown at deps/icu-small/source/tools/escapesrc/escapesrc.cpp:144

 * @return true on failure
 */
bool appendUtf8(std::string &outstr,
                const std::string &linestr,
                size_t &pos,
                size_t chars) {
  char tmp[9];
  for(size_t i=0;i<chars;i++) {
    tmp[i] = linestr[++pos];
  }
  tmp[chars] = 0;
  unsigned int c;
  sscanf(tmp, "%X", &c);
  UChar32 ch = c & 0x1FFFFF; 

  // now to append \\x%% etc
  uint8_t bytesNeeded = U8_LENGTH(ch);
  if(bytesNeeded == 0) {
    fprintf(stderr, "Illegal code point U+%X\n", ch);
    return true;
  }
  uint8_t bytes[4];
  uint8_t *s = bytes;
  size_t i = 0;
  U8_APPEND_UNSAFE(s, i, ch);
  for(size_t t = 0; t<i; t++) {
    appendByte(outstr, s[t]);
  }
  return false;
}

/**
 * Fixup u8"x"
 * @param linestr string to mutate. Already escaped into \u format.
 * @param origpos beginning, points to 'u8"'
 * @param pos end, points to "
 * @return false for no-problem, true for failure!

View on GitHub (pinned to 1b2de5e052)

Solutions

1. Find the offending \U literal on the line reported by escapesrc and correct it to a value <= U+10FFFF.
2. If the literal was meant to be a narrower escape, use \uXXXX (<= U+FFFF) or split into a surrogate pair.
3. Regenerate or re-export the source file so wide character literals stay within the valid Unicode range.

Example fix

// before
const char* s = u8"\U00120000";

// after
const char* s = u8"\U0001F600";

// scan source for wide escapes and reject out-of-range values before escapesrc runs
import re
for m in re.finditer(r'\\U([0-9A-Fa-f]{5,8})', src):
    if int(m.group(1), 16) > 0x10FFFF:
        raise ValueError(f'code point {m.group(0)} exceeds U+10FFFF')

When it happens

Trigger: A source file contains a \U escape whose hex value, after masking with 0x1FFFFF, is in the range 0x110000..0x1FFFFF (e.g. \U00110000 or larger), or a truncated/malformed wide hex literal that sscanf reads as an oversized value.

Common situations: Hand-authored source with a typo in a \UXXXXXXXX literal; generated code emitting out-of-range code points; copy-paste of an astral-plane literal with an extra digit.

Related errors

• Cannot do u8'...'\n
• Illegal utf-8 sequence at Column: %d\n
• %s: usage: %s infile.cpp outfile.cpp
• Not a 'u'?
• Quote is '%c' - not sure what to do.\n

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/2685b922ccac3a36. Report an issue: GitHub.