Request to drop daft GNU extension

[Neil Booth <NeilB at earthling dot net>]

I'd like to request we drop a GNU extension.  I realise this will make
me unpopular with the backwards compatibility crowd, but there are
sound reasons for doing so.

The one I'd like to drop is the following kludged meaning of ##
(taking the example from the info manual)

#define eprintf(format, args...) fprintf (stderr, format , ## args)

My reasons for doing so are as follows:

1) This use of ## has nothing to do with its true meaning of token
   pasting, certainly when our macro expanding is token-based.
   See point 4) for an example of why this is a problem.

2) It is entirely redundant.  The justification put forth in the manual
   is resolving the "embarrassment" of an extra comma when invoked as

   eprintf ("success!\n", )

   which gives

   fprintf (stderr, "success!\n", )

   However, this is just masking the fact that your macro really has
   more arguments in the variable part than you're claiming it has,
   and thus I would suggest that it should be redefined as:-

   #define eprintf(format...) fprintf (stderr, format)

   and then the invocations

   eprintf ("%s:%d: ", input_file_name, line_number)
   eprintf ("success!\n")

   give the desired result in both cases.  This redundancy is what
   convinces me there will never be anything like this in the standard.

3) It prevents correct usage of ##.  Consider

   #define foo(a, b...) a ## b

   Invoking this macro with

   foo (1, )

   drops the 1 to give an empty expansion, whereas it should expand as
   the single token <1>.

4) It makes the macro expansion code uglier than it already is.


I have implemented it in the new macro expander, but I don't think we
should implement it.  Comments?

Neil.