bug#40832: Audacity does not work with PulseAudio

[Leo Famulari <leo@famulari.name>]

On Tue, Apr 28, 2020 at 11:25:32PM +0200, Ludovic Courtès wrote:
> Could it be that the problem is in Audacity and not in alsa-lib?

I'm not 100% sure but I don't think so.

The function snd_config_hooks_call() is from alsa-lib I can't find any
way in alsa-lib for it work in this case, even though it aims to work by
default on systems with plugins in '/usr/lib/alsa-lib' or similar.

The lookup is performed in alsa-lib's 'src/dlmisc.c', by the function
snd_dlopen(), and it only looks in the hard-coded path provided by the
ALSA_PLUGIN_DIR C object macro, which ends up being alsa-lib's own store
directory.

> I can do this with mpg123:
> 
> --8<---------------cut here---------------start------------->8---
> $ cat ~/.asoundrc
> pcm.!default {
>     type pulse
> }
> $ mpg123 -o alsa …
> --8<---------------cut here---------------end--------------->8---
> 
> and the sound goes through PulseAudio.

Is that on Guix System or another distro? On Guix System, this is
handled by the service alsa-service-type.

On Debian, using mpg123 from Guix, and with your ~/.asoundrc, it fails
in the same way as Audacity:

------
% mpg123 -o alsa ...
High Performance MPEG 1.0/2.0/2.5 Audio Player for Layers 1, 2 and 3
	version 1.25.13; written and copyright by Michael Hipp and others
	free software (LGPL) without any warranty but with best wishes
ALSA lib conf.c:3683:(snd_config_hooks_call) Cannot open shared library libasound_module_conf_pulse.so (/gnu/store/nyylgcnzmbw8wrn4sna2crl0g7zxxh33-alsa-lib-1.2.2/lib/alsa-lib/libasound_module_conf_pulse.so: libasound_module_conf_pulse.so: cannot open shared object file: No such file or directory)
ALSA lib pcm.c:2642:(snd_pcm_open_noupdate) Unknown PCM default
[src/libout123/modules/alsa.c:181] error: cannot open device default
[src/libout123/libout123.c:455] error: Found no driver out of [alsa] working with device <default>.
main: [src/mpg123.c:314] error: out123 error 3: failure loading driver module
------