Re: Using @bindir@ etc. in C headers

[Florian Weimer]

* Michael Orlitzky:

> On 6/5/20 6:57 AM, Florian Weimer wrote:
>> I would like to define macros containing the standard paths, like this:
>> 
>> #define BINDIR "@bindir@"
>> 
>> It does not work due to this code in lib/autoconf/general.m4 (which
>> appears to be predate DESTDIR support):
>> 
>> ...
>> 
>> Is there are generally approved way to work around this?  The manual
>> tells us to use -D preprocessor arguments, but I'd prefer the
>> explicitness of defining the macros via a header file.
>
> The autoconf manual's "Installation Directory Variables" section says
> the following...
>
>   Similarly, you should not rely on AC_CONFIG_FILES to replace datadir
>   and friends in your shell scripts and other files; instead, let make
>   manage their replacement. For instance Autoconf ships templates of its
>   shell scripts ending with `.in', and uses a makefile snippet similar
>   to the following to build scripts like autoheader and autom4te:
>
>      edit = sed \
>              -e 's|@datadir[@]|$(pkgdatadir)|g' \
>              -e 's|@prefix[@]|$(prefix)|g'
>
>      autoheader autom4te: Makefile
>              rm -f $@ $@.tmp
>              $(edit) '$(srcdir)/$@.in' >$@.tmp
>              chmod +x $@.tmp
>              chmod a-w $@.tmp
>              mv $@.tmp $@
>
>      autoheader: $(srcdir)/autoheader.in
>      autom4te: $(srcdir)/autom4te.in
>
> Not very aesthetically pleasing, but it gets the job done.

It would like to get config.status expansion going, among other things.
It's nice to consolidate these things in a single place, and avoid
scattering such constructs and several places.

What do you think about this?

dnl LIBC_SUBST_EXPANDED(VAR) creates a substitution variable
dnl VAR_expanded with the shell-expanded value of VAR.  In this context,
dnl ${exec_prefix} is expanded to the empty string.
AC_DEFUN([LIBC_SUBST_EXPANDED],
[exec_prefix= eval $1_expanded="${$1}"
AC_SUBST($1_expanded)
])

And then towards the end of configure.ac:

LIBC_SUBST_EXPANDED(libdir)

Thanks,
Florian