Re: checking for headers presence even if usable

[Ralf Wildenhues]

Hi Karl,

* Karl Berry wrote on Tue, Apr 22, 2008 at 01:29:27AM CEST:
> I'm not sure if this is really a bug, but I thought I'd mention it.  It
> seems that autoconf 2.62 checks headers for "presence" even if they are
> already determined to have "usability".

Then the text of the output is not good enough.  The first check is a
compile check, the second one a preprocess check.  If they disagree in
one way or another, you get a warning.

Until several years ago, that warning said to write to bug-autoconf if
the package author didn't provide a bug report address.  From the mail
echo that this provokes to this day, I would say that "present but
cannot be compiled" is much more likely to happen than "accepted by the
compiler, rejected by the preprocessor", but both happen.  The latter
typically with challenged or wrong preprocessor settings (e.g., /lib/cpp
on Solaris).

Hope that helps.

Cheers,
Ralf