Re: AC_SUBST'ing foodir correctly?

[Wouter Verhelst]

Hi Mathieu,

Sorry for the late reply -- been busy, you know how it goes.

On Mon, May 30, 2016 at 04:48:57PM +0200, Mathieu Lirzin wrote:
> Wouter Verhelst <address@hidden> writes:
> 
> > On Tue, May 24, 2016 at 06:11:47PM +0200, Mathieu Lirzin wrote:
> >> 
> >> ‘systemdsystemunitdir’ seems not affected by DESTDIR because IIUC
> >> PKG_CHECK_VAR set it to something like "/lib/systemd/system" instead of
> >> "${libdir}/systemd/system".
> >> 
> >> I suppose it would work better to define it manually like
> >> this:
> >> 
> >>   if SYSTEMD
> >>     systemdunitdir = $(libdir)/systemd/system
> >>     systemdunit_DATA = address@hidden
> >>   endif
> >
> > Well. That would work, yes, but it wouldn't work *better*. The whole
> > point is that I do not want to hardcode such things, so that if a user
> > installs systemd units in </usr/local/brokenstuff/systemd> and the
> > pkg-config files are where they need to be, everything works as expected.
> 
> You are right, that would be better.  My understanding is that
> pkg-config files are supposed to define variables in terms of 'prefix'
> as described in pkg-config(1)
> 
> --8<---------------cut here---------------start------------->8---
>   prefix=/home/hp/unst   # this defines a variable
>   exec_prefix=${prefix}  # defining another variable in terms of the first
>   libdir=${exec_prefix}/lib
>   includedir=${prefix}/include
> --8<---------------cut here---------------end--------------->8---
> 
> but “systemd.pc” isn't doing that.

I'm not convinced that is the right way to fix this. Yes, perhaps the
systemd .pc file could export $prefix-prefixed variables. However, that
doesn't help -- it's *systemd*'s prefix it would be prefixing with, not
nbd's prefix. If someone installed systemd with --prefix=/opt, and then
installed nbd with --prefix=/usr, then in your suggestion, nbd would be
installing the systemd unit files into /usr/lib/systemd, where they
should really have been installed into /opt/lib/systemd.

It's not limited to that kind of stuff, either -- it would also break
if someone were to configure systemd with an explicit --libdir=, where
the .pc file is generated with AC_CONFIG_FILES.

Please remember that I'm installing a file for systemd to use, not a
file for nbd to use (in this particular case it's a systemd
configuration file, but it could equally well have been a plugin, or an
extension, or whatever).

> > I was under the impression that automake looks at DESTDIR for every
> > foodir it looks at, but apparently that's not the case then? That seems
> > broken; after all, I don't think a staging directory should depend on
> > whether or not something was part of a given prefix. Is there any
> > explanation available somewhere on why this behaviour occurs? Would a
> > patch that changes this behaviour be acceptable?
> 
> Every default installation directories are expected to be subdirectories
> of the 'prefix' variable.  This is verified by ‘make distcheck’ and
> specified in GNU coding standards:
> 
>   
> https://www.gnu.org/prep/standards/html_node/Directory-Variables.html#Directory-Variables
> 
> So it is unlikely that a patch is going to be accepted in Automake.

Not even for the --foreign mode of automake?

> However I guess the default pkg-config file could be fixed in Systemd.

That would mean the nbd build will break for everyone who did a
non-default build of systemd... not a very attractive proposal.

-- 
< ron> I mean, the main *practical* problem with C++, is there's like a dozen
       people in the world who think they really understand all of its rules,
       and pretty much all of them are just lying to themselves too.
 -- #debian-devel, OFTC, 2016-02-12