bug#31825: guix offload fails with guix-authenticate error

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hello!

I've read the documentation carefully many times, but I still can't make
`guix offload' work. It always fails like so:

--8<---------------cut here---------------start------------->8---
guix offload test
guix offload: testing 1 build machines defined in '/etc/guix/machines.scm'...
guix offload: '192.168.1.105' is running guile (GNU Guile) 2.2.3
guix offload: Guix is usable on '192.168.1.105' (test returned "/gnu/store/883yjkl46dxw9mzykykmbs0yzwyxm17z-test")
sending 1 store item to '192.168.1.105'...
exporting path `/gnu/store/wrv01knf5xa76j73afscj066pbqq1na3-export-test'
guix offload: error: build failed: program `guix-authenticate' failed with exit code 1
--8<---------------cut here---------------end--------------->8---

In GDB, I've attempted to follow the forks but without success. The
most useful hint I've got was the following message about
guix-authenticate not being found:

--8<---------------cut here---------------start------------->8---
sudo gdb --args guix-daemon --build-users-group=guixbuild
GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.5) 7.11.1
[...]
(gdb) r
Starting program: /home/mcournoyer/src/guix/guix-daemon --build-users-group=guixbuild
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/gnu/store/4sqaib7c2dfjv62ivrg9b8wa7bh226la-glibc-2.26.105-g0890d5379c/lib/libthread_db.so.1".
accepted connection from pid 2241, user mcournoyer
accepted connection from pid 29024, user mcournoyer
accepted connection from pid 2241, user mcournoyer
accepted connection from pid 29068, user mcournoyer
error: executing `guix-authenticate': No such file or directory
--8<---------------cut here---------------end--------------->8---

Things I've tried without success:

1. Installing guix into my user's profile and then this to the ~/.bashrc
on the remote machine:

--8<---------------cut here---------------start------------->8---
GUIX_PROFILE=$HOME/.guix-profile
source $GUIX_PROFILE/etc/profile

# Hack to make guix-authenticate available
export PATH=$PATH:$GUIX_PROFILE/libexec
--8<---------------cut here---------------end--------------->8---

2. Noticing that the guix-daemon I was debugging (the one at
~/src/guix/guix-daemon) was using nixLibexecDir = "/usr/local/libexec"
and that the guix-daemon has code doing this in guix-daemon.cc:469:

--8<---------------cut here---------------start------------->8---
      /* Hackily help 'local-store.cc' find our 'guix-authenticate' program, which
	 is known as 'OPENSSL_PATH' here.  */
      std::string search_path;
      search_path = settings.nixLibexecDir;
      if (getenv ("PATH") != NULL)
	{
	  search_path += ":";
	  search_path += getenv ("PATH");
	}

      setenv ("PATH", search_path.c_str (), 1);
--8<---------------cut here---------------end--------------->8---

I tried:

--8<---------------cut here---------------start------------->8---
sudo ln -s /var/guix/profiles/per-user/mcournoyer/guix-profile/libexec /usr/local/libexec
--8<---------------cut here---------------end--------------->8---

I'm motivated to get this working; would be pleased to debug further
given fresh ideas.

Thanks,

Maxim