[Bug c++/105626] New: -Wformat should accept u8"" strings

[drepper.fsp+rhbz at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105626

            Bug ID: 105626
           Summary: -Wformat should accept u8"" strings
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: drepper.fsp+rhbz at gmail dot com
  Target Milestone: ---

The discussion about this topic on gcc@
(https://gcc.gnu.org/pipermail/gcc/2022-May/238673.html) ended with the
conclusion that gcc should not disregard the cast in code like this:

#include <stdio.h>

int main()
{
  printf((const char*) u8"test %d\n", 1);
  return 0;
}

With -Wformat this code produces with gcc 12:

t.cc: In function ‘int main()’:
t.cc:5:24: warning: format string is not an array of type ‘char’ [-Wformat=]
    5 |   printf((const char*) u8"test %d\n", 1);
      |                        ^~~~~~~~~~~~~

Since

a) there are no I/O functions for u8 strings in C++20
b) using u8 strings is necessary in reliable code
c) it is safe to perform the analysis -Wformat does on u8 strings

I suggest that u8 strings are allowed when testing for -Wformat.