Re: What is meant by, "XXX does not appear in AM_CONDITIONAL"?

[Stepan Kasal <kasal at ucw dot cz>]

Hi Bruce,

On Mon, Jan 10, 2005 at 08:35:27AM -0800, Bruce Korb wrote:
> > if [some-shell-script-test]
> > then
> >   ...
> >   AM_CONDITIONAL([XXX], [true])
> > else
> >   ...
> >   AM_CONDITIONAL([XXX], [false])
> > fi

> reading the docs some more, they explicitly state to not do this.

I re-read the node ``Conditionals'' of automake manual (CVS version) just
now.  I don't see any problem:

``you must arrange for _every_ `AM_CONDITIONAL' to be invoked every
  time `configure' is run''

and you are doing this.

But Ralf said that this practice is not reliable, and I'd believe his
experience.

If I can add a bit of my experience, then I witness that using commands
`true' or `false' as the second part of AM_CONDITIONAL is often sign
of bad style.  This might apply to your ``set_XXX'' too.  Let me explain:

You said:
> This is more-or-less exactly what is going on, except that
> the "some-shell-script-test" includes (but is not exactly
> limited to) some compile-and-link macros.

Oh, then the following if should not probably test for `$?', but for
a variable value, or something else which represents the result of the
previous tests.

In most cases, you can follow this pattern:

AC_CHECK_FOR_ELEPHANTS(...)

if test "x$ELEPHANTS_FOUND" = xyes; then
	...
else
	...
fi
AM_CONDITIONAL([XXX], [test "x$ELEPHANTS_FOUND" = xyes])

or perhaps this pattern:

AC_CHECK_FOR_ELEPHANTS(...)

HAVE_ELEPHANTS=yes
case $ELEPHANT_TYPE in
indian)
	...;;
african)
	...;;
*)
	HAVE_ELEPHANTS=no;;
esac
AM_CONDITIONAL([HAVE_ELEPHANTS], [test $HAVE_ELEPHANTS = yes])
AM_CONDITIONAL([INDIAN_ELEPHANTS], [test "x$ELEPHANT_TYPE" = xindian])

A side note: yes, you could set HAVE_ELEPHANTS to `true' or `false' here
and call ``AM_CONDITIONAL([HAVE_ELEPHANTS], [$HAVE_ELEPHANTS])''.
It's a matter of taste.

Another side note: this example probably explains the Ralf's recommendation
to have AM_CONDITIONALa out of any if is right: you could easily imagine
that one forgets to set INDIAN_ELEPHANTS when no elephants are available.

Have a nice day,
	Stepan