Bug#945057: libnet-dbus-perl FTCBFS: uses the build architecture pkg-config

[gregor herrmann]

On Tue, 19 Nov 2019 06:09:15 +0100, Helmut Grohne wrote:

> libnet-dbus-perl fails to find the dbus library. It does so using the
> build architecture pkg-config, but libdbus is only installed for the
> host architecture. Now I'm unsure how to fix this. 

Thanks for the bug report, that's an interesting one indeed.

> The common wisdom is
> to prefix tools with the host architecture triplet. The other wisdom is
> to pass tools as environment variables. The perl ecosystem seems to
> follow a different route: Record paths in Config.pm. Unfortunately,
> Config.pm neither has the triplet nor does it have pkg-config. Bummer.

So we're looking for something like 'x86_64-linux-gnu' in Config.pm
(or pass PKG_CONFIG=x86_64-linux-gnu-pkg-config in the environment),
right?

For the former,
    % perl -MConfig=config_sh -e 'print config_sh();' | grep x86_64-linux-gnu
has quite a few results but never x86_64-linux-gnu alone.

> So what is a good way to get the right pkg-config into the Makefile.PL?

(And Build.PL.)
I guess that's a question for Niko …
 
> I don't like the patch, because it creates two routes to communicate the
> host architecture: Config.pm and environment. If these communication
> methods are not in sync, bad things happen. I'd much prefer to have a
> single source of truth here.

Ack.
 
> Consider this bug an "example bug". Using pkg-config in Makefile.PL is
> likely something that happens elsewhere. It'll need fixing a few times.

Right, but the good news is that I only find 23 packages (of the
pkg-perl maintained ones) which use pkg-config in
{Makefile,Build}.PL.

> I'd like to get to a good solution here before filing more of them,
> because libnet-dbus-perl nicely isolates this issue.

Ack.


Random thought: I wonder if PkgConfig ("a pure perl version of
pkg-config"), packaged as libpkgconfig-perl, providing
/usr/bin/ppkg-config, could be a helpful workaround. This would still
require a changed build dependency and a s/pkg-config/ppkg-config/ in
{Makefile,Build}.PL [0] but would spare us any path or architecture
hassles. Maybe :)


*Some times later*


So, I did my first cross build :) (with cowbuilder and the help of
https://wiki.debian.org/CrossCompiling ) and it worked with:

+               libpkgconfig-perl:native,
+               perl-xs-dev,
+               perl:native

and a patch which does s/pkg-config/ppkg-config/ in Makefile.PL, and
I get:

libnet-dbus-perl_1.1.0-7_i386.deb
---------------------------------
 new Debian package, version 2.0.
 size 183472 bytes: control archive=3128 bytes.
     917 bytes,    19 lines      control
    8013 bytes,    88 lines      md5sums
 Package: libnet-dbus-perl
 Version: 1.1.0-7
 Architecture: i386


I've pushed these changes to a new "cross-945057" branch in
https://salsa.debian.org/perl-team/modules/packages/libnet-dbus-perl.git



Cheers,
gregor

[0] or `use PkgConfig …;' programmatically

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