Comment 30 for bug 1109327

Created attachment 6474
test conversion from UTF-8 and handling of incomplete characters (fails)

I assume Joseph means to spend some time to avoid future authors breaking
wprintf now that our attention's on it, not to avoid breaking wprintf when
applying your patch. Your patch doesn't even touch wprintf code.

I tried writing a wprintf testcase, and it's not gone so well. For
example, I tried

  wchar_t buf[1000];
  int n;

  if (!setlocale(LC_ALL, "ja_JP.UTF-8)) {
    perror("setlocale");
    return 1;
  }
  n = swprintf(buf, sizeof(buf)/sizeof(wchar_t), L"%3s",
        "\xef\xbd\xa1g\xef\xbd\xa2h\xef\xbd\xa3i\xef\xbd\xa4j");

I expected swprintf to return 3 and buf to equal

  { 0xff61, 'g', 0xff62, 0 }

Instead, swprintf returns 8 and converts the entire string.