Re: if (...) then; AC_PROG_CC else AC_PROG_CC fi doesn't work?

[Brooks Moses]

Eric Blake wrote:
> This is a known 'feature' of autoconf.  In general, invoking macros with side-
> effects inside of raw 'if' blocks is dangerous; there are two common failure 
> scenarios - side effects happen regardless of whether the shell code containing 
> the macro name is executed (because autoconf generates the side-effect code 
> into a different m4 diversion), or, as in your case, side effects only happen 
> on the first use of the macro (because autoconf AC_REQUIRE's the side-effect to 
> avoid redundant output of one-shot initialization).  You can try using AS_IF 
> instead of raw shell 'if' for wrapping the AC_PROG_CC calls, since the purpose 
> of AS_IF is to output a shell conditional AND correctly handle side effects of 
> macros within that shell conditional.  But in your case, the easiest thing to 
> do is fix your autoconf.ac:
>
> AC_INIT
> AC_ARG_ENABLE(foo)
> AC_PROG_CC([gcc])
> if test "$enable_foo"; then
>    echo "enabled"
> else
>    echo "disabled"
> fi

Thanks!  Unfortunately, however, that "fixes" it by breaking the desired 
functionality.  The point of enable_foo is not the echo statements, but 
the fact that AC_PROG_CC uses the "[gcc]" list when foo is enabled, and 
uses the default program list when foo is disabled.

Is there some way to define a variable argument to AC_PROG_CC to get 
this functionality?  I'd like to do something like the following, if I 
could:

AC_INIT
AC_ARG_ENABLE(foo)
if test "$enable_foo"; then
  echo "enabled"
  cc_list=[gcc]
else
  echo "disabled"
  cc_list=
fi
AC_PROG_CC($cc_list)

However, this doesn't actually work; with foo disabled, AC_PROG_CC just 
looks in the empty list for acceptable C compilers, and of course 
doesn't find anything.

If it's not possible to do something like this, I'll have a look at AS_IF.

- Brooks