Re: present but cannot be compiled (Was: spurious request to report bug?)

[Dave Love]

Akim Demaille <address@hidden> writes:

> Please, report this to the package maintainers, as it's a configure.ac
> problem.

Please re-read what I wrote.  The message saying to report a bug
against autoconf comes from autoconf 2.57's headers.m4.  If you want
people to report a bug against the relevant package, it should say so.
(If people actually obeyed the instructions I guess you'd be swamped.)

> The Autoconf 2.57 doc says:

I know, and I fixed it in Emacs, as I said below.

>       Previous versions of Autoconf merely checked whether the header was
>    accepted by the preprocessor.  This was changed because the old test was
>    inappropriate for typical uses.  Headers are typically used to compile,
>    not merely to preprocess, and the old behavior sometimes accepted
>    headers that clashed at compile-time.  If you need to check whether a
>    header is preprocessable, you can use `AC_PREPROC_IFELSE' (*note
>    Running the Preprocessor::).
>    
>       This scheme, which improves the robustness of the test, also requires
>    that you make sure that headers that must be included before the
>    HEADER-FILE be part of the INCLUDES, (*note Default Includes::).  If
>    looking for `bar.h', which requires that `foo.h' be included before if
>    it exists, we suggest the following scheme:
>    
>    
>    AC_CHECK_HEADERS([foo.h])
>    AC_CHECK_HEADERS([bar.h], [], [],
>    [#if HAVE_FOO_H
>    # include <foo.h>
>    # endif
>    ])
> 
> Thanks!
> 
> | When configuring the current Emacs source on SunOS 4.1.4 with the
> | bundled cc, configure says this from an AC_CHECK_HEADERS check for
> | sys/resource.h done with autoconf 2.57:
> | 
> |   checking sys/resource.h usability... no
> |   checking sys/resource.h presence... yes
> |   configure: WARNING: sys/resource.h: present but cannot be compiled
> |   configure: WARNING: sys/resource.h: check for missing prerequisite 
> headers?
> |   configure: WARNING: sys/resource.h: proceeding with the preprocessor's 
> result
> |   configure: WARNING:     ## ------------------------------------ ##
> |   configure: WARNING:     ## Report this to address@hidden ##
> |   configure: WARNING:     ## ------------------------------------ ##
> |   checking for sys/resource.h... yes
> | 
> | I'm surprised it says to report a bug against autoconf.  (I'll fix the
> | issue in Emacs by using sys/time.h.)  The relevant config.log fragment
> | is: