nodejs/node · error

Cannot do u8'...'\n

Error message

Cannot do u8'...'\n

What it means

escapesrc explicitly rejects the u8'x' form (UTF-8 narrow character literal). It supports u8"..." strings but not the single-character u8'...' literal, which the comment at fixAt documents as unsupported. The tool returns an error rather than emit incorrect output.

Solutions

1. Rewrite u8'x' literals as plain 'x' (char) or as a u8"x" single-character string, which escapesrc does support.
2. If a multi-byte UTF-8 character is required, use u8"\uXXXX" string form instead of a char literal.
3. Pre-process or post-process the source to convert u8'...' forms before running escapesrc.

Example fix

// before
char c = u8'A';

// after
char c = 'A';
// or, if a UTF-8 string is intended:
const char* c = u8"A";

// pre-scan: rewrite u8'x' forms to supported forms before escapesrc
import re
src2 = re.sub(r"u8'(.)'", lambda m: f"u8\"{m.group(1)}\"" if ord(m.group(1)) > 127 else f"'{m.group(1)}'", src)

When it happens

Trigger: A source line contains a u8-prefixed single-quoted character literal, e.g. u8'A' or u8'\n'. fixAt detects (quote == '\'' && utf8) and fails the line.

Common situations: Modern C++17+ code using u8 char literals; porting code that previously used char literals to UTF-8 literals for consistency; code generated by a tool that emits u8'...' uniformly.

Related errors

• Illegal code point U+
• Illegal utf-8 sequence at Column
• Not a 'u'?
• Quote is '%c' - not sure what to do.\n
• : could not open input file \n

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/845e62e89ddaa253. Report an issue: GitHub.

Appendix: source

Thrown at deps/icu-small/source/tools/escapesrc/escapesrc.cpp:233

  pos++; // past 'u'

  bool utf8 = false;
  
  if(linestr[pos] == '8') { // u8"
    utf8 = true;
    pos++;
  }
  
  char quote = linestr[pos];

  if(quote != '\'' && quote != '\"') {
    fprintf(stderr, "Quote is '%c' - not sure what to do.\n", quote);
    return true;
  }

  if(quote == '\'' && utf8) {
    fprintf(stderr, "Cannot do u8'...'\n");
    return true;
  }

  pos ++;

  //printf("u%c…%c\n", quote, quote);

  for(; pos < linestr.size(); pos++) {
    if(linestr[pos] == quote) {
      if(utf8) {
        return fixu8(linestr, origpos, pos); // fix u8"..."
      } else {
        return false; // end of quote
      }
    }
    if(linestr[pos] == '\\') {
      pos++;
      if(linestr[pos] == quote) continue; // quoted quote

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