Re: AC_CACHE_CHECK

[Ralf Wildenhues]

Hello,

* Thomas Dickey wrote on Sun, Sep 05, 2010 at 03:09:20PM CEST:
> On Sun, 5 Sep 2010, Russell Shaw wrote:
> >Thomas Dickey wrote:
> >>On Sun, 5 Sep 2010, Russell Shaw wrote:
> >>>When should AC_CACHE_CHECK be used? Whenever the user uninstalls
> >>>something, wouldn't the cache become invalid?
> >>
> >>...only if the user happened to uninstall something during the configure
> >>process.  After that, AC_CACHE_CHECK is irrelevant.
> >
> >But if the user uninstalls libfoo then later re-runs ./configure,
> >won't libfoo still be assumed to be installed?
> 
> sure.  That sort of thing was why (for a long time) autoconf removed
> the cache on startup.  Now that you're mentioning it, I seem to recall
> a recent undoing of that.

I can't remember that either autoconf nor configure would remove
config.cache, for any Autoconf >= 2.59.  'make distclean' from an
automake-generated Makefile does that.

But yes, you are supposed to not reuse the cache file after changing
your system.

With that in mind, AC_CACHE_CHECK should be used freely for any test
that is expensive or should be overridable by the user (because she
might know better), and that is amenable to single-entrance logic
(i.e., isn't run in a loop) and a unique cache variable name.

Cheers,
Ralf