Pre-DR: variadic standard library functions
===========================================

To what extent should the variadic functions in <stdio.h> and
<wchar.h> be required to act as if they use the <stdarg.h> macros to
access arguments?

There are at least three cases involved.  The first relates to an
actual conformance dispute; the others are less likely to relate to
observable behavior of actual implementations.

1. Arguments of correct promoted type, but out of range for unpromoted
   type.

#include <stdio.h>

void
f(void)
{
  // Suppose that UCHAR_MAX == 255.
  printf("%hhu", 256);
}

Here, the argument is of type int, the correct promoted type, but even
printf implemented using the <stdarg.h> macros only can tell that it
did not arise from an unsigned char.  Is this defined, or should it
be?  If not, what purpose does the wording about printf converting the
argument back to unsigned char before printing serve?  One library
implementor claims that another library implementation does not
conform because it prints 256, but the argument was not an unsigned
char, so is there undefined behavior?

2. Arguments of correct promoted type, and in range for unpromoted
   type, but not of the unpromoted type.

#include <stdio.h>

void
f(void)
{
  // Suppose that unsigned char promotes to int.
  printf("%hhu", 0);
}

Here, %hhu expects an unsigned char, which has been promoted to int,
but has been passed an int not derived from an unsigned char.  Is this
defined, or should it be?

3. Arguments of incorrect type, allowed for va_arg by 7.15.1.1#2.

#include <stdio.h>

void
f(void)
{
  printf("%x", 0);
}

Here, an int argument is passed where an unsigned int is expected, but
the value is representable in both types.  Is this defined, or should
it be?