Comment by kazinator

Example:

  #include <stdio.h>
  #include <string.h>

  #define strlcpy(dst, src, size) ((size_t) snprintf(dst, size, "%s", src))

  size_t (strlcpy)(char *dst, const char *src, size_t size)
  {
    return strlcpy(dst, src, size);
  }

  int main(void)
  {
    char littlebuf[8];
    strlcpy(littlebuf, "Supercalifragilisticexpealidocious", sizeof littlebuf);
    return 0;
  }


  strlcpy.c: In function ‘main’:
  strlcpy.c:4:63: warning: ‘%s’ directive output truncated writing 34 bytes into a region of size 8 [-Wformat-truncation=]
   #define strlcpy(dst, src, size) ((size_t) snprintf(dst, size, "%s", src))
                                                               ^
  strlcpy.c:14:22:
     strlcpy(littlebuf, "Supercalifragilisticexpealidocious", sizeof littlebuf);
                      ~
  strlcpy.c:14:3: note: in expansion of macro ‘strlcpy’
     strlcpy(littlebuf, "Supercalifragilisticexpealidocious", sizeof littlebuf);
   ^~~~~~~
  strlcpy.c:4:34: note: ‘snprintf’ output 35 bytes into a destination of size 8
   #define strlcpy(dst, src, size) ((size_t) snprintf(dst, size, "%s", src))
                                   ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  strlcpy.c:14:3: note: in expansion of macro ‘strlcpy’
     strlcpy(littlebuf, "Supercalifragilisticexpealidocious", sizeof littlebuf);
     ^~~~~~~

If glibc doesn't do something in the header file such that we get similar diagnostics for its strlcpy, we can make the argument that this is detrimental to the program.