broken ac_fn_c_check_type function in configure script

[John Spencer]

this check has 2 issues:
a) it does the check twice if the first test succeeds, wasting precious time
b) it uses sizeof(( $2 )) in the second ac_fn_c_try_compile invocation 
which is invalid C


root:/src$ cat test.c
typedef unsigned long size_t;
int main () {
if (sizeof ((size_t)))
  return 0;
return 0;
}
root:/src$ gcc test.c
test.c: In function 'main':
test.c:3:22: error: expected expression before ')' token

here's the extracted function from version 1.4.6 configure script

# ---
# Tests whether TYPE exists after having included INCLUDES, setting cache
# variable VAR accordingly.
ac_fn_c_check_type ()
{
  as_lineno=${as_lineno-$1} 
as_lineno_stack=as_lineno_stack=$as_lineno_stack

  { $as_echo $as_me:${as_lineno-$LINENO}: checking for $2 5
$as_echo_n checking for $2...  6; }
if eval \${$3+:} false; then :
  $as_echo_n (cached)  6
else
  eval $3=no
  cat confdefs.h - _ACEOF conftest.$ac_ext
/* end confdefs.h.  */
$4
int
main ()
{
if (sizeof ($2))
 return 0;
  ;
  return 0;
}
_ACEOF
if ac_fn_c_try_compile $LINENO; then :
  cat confdefs.h - _ACEOF conftest.$ac_ext
/* end confdefs.h.  */
$4
int
main ()
{
if (sizeof (($2)))
return 0;
  ;
  return 0;
}
_ACEOF
if ac_fn_c_try_compile $LINENO; then :

else
  eval $3=yes
fi
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
fi
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
fi
eval ac_res=\$$3
   { $as_echo $as_me:${as_lineno-$LINENO}: result: 
$ac_res 5

$as_echo $ac_res 6; }
  eval $as_lineno_stack; ${as_lineno_stack:+:} unset as_lineno

} # ac_fn_c_check_type

--JS

Re: broken ac_fn_c_check_type function in configure script

[Bojan Smojver]

On Wed, 2012-04-25 at 21:38 +0200, John Spencer wrote:
 a) it does the check twice if the first test succeeds, wasting
 precious time
 b) it uses sizeof(( $2 )) in the second ac_fn_c_try_compile invocation
 which is invalid C 

From what I can tell, both of these things are the consequence of the
code generated by autoconf, not APR code.

-- 
Bojan