Re: Anyone remember what AC_PROG_GCC_TRADITIONAL was testing for?

[Paul Eggert]

That macro dates back to /usr/include header files that would play 
tricks like this

     #define _IO(n, x) (('n'<<8)+x) 

     #define TIOCFOO _IO(T, 1) 


and would expect TIOCFOO to be equivalent to (('T'<<8)+1). This sort of 
trick worked with K&R C compilers but does not work with C89+. To work 
around the problem back in the day, you needed to use 'gcc -traditional'.

Using -traditional had obvious problems, though, so GCC soon changed its 
installation procedure "fixincludes" to make fixed copies of these 
K&R-assuming headers during installation, and to compile by including 
the fixed copies. This was around 1990. I was involved with some of that 
header-munging effort but have blessedly forgotten most of the details. 
A descendant of the fixincludes work is still in GCC's source code 
(which is where I got the above example).

AC_PROG_GCC_TRADITIONAL has not been needed for thirty years, and was 
declared obsolescent in Autoconf 2.60 (2006-06-05). Also, the Autoconf 
manual (as of the next version) states Autoconf assumes C89 or later. So 
if there's any issue with AC_PROG_GCC_TRADITIONAL at all, I suggest 
replacing its definition with:

  AU_DEFUN([AC_PROG_GCC_TRADITIONAL])

and updating documentation and tests and etc. accordingly.