Dear Oleg,

At that time, spice-vdagent package had a bug. So I modified spice.scm to
fix it. To make it applied to the system, I put that file into
~/my-guix/gnu/packages and ran `guix system reconfigure /etc/config.scm -L
~/my-guix`. But it took long time because there were many packages to be
built without substitutes. So I just did dry-run.

Now, spice-vdagent's bug is fixed. Thus, just for test, I modified the
spice.scm in ~/my-guix/gnu/packages and try reconfiguring the system.
Spice.scm is modified as:

--- spice.scm.orig    2018-11-19 04:05:33.543753567 +0900
+++ spice.scm    2018-11-19 03:09:09.283971057 +0900
@@ -252,7 +252,7 @@
             (substitute* "data/spice-vdagent.desktop"
               (("Exec=/usr/bin/spice-vdagent")
                (string-append "Exec=" (assoc-ref outputs "out")
-                              "/bin/spice-vdagent")))
+                              "/bin/spice-vdagent\n")))
              #t)))))
     (inputs
       `(("alsa-lib" ,alsa-lib)

I have dry-run's.
[1] guix system reconfigure /etc/config.scm -n -L ~/my-guix :
with_spice_with_loadpath.log
(12K)

<https://mail.google.com/mail/u/0?ui=2&ik=f97d85874d&attid=0.1&permmsgid=msg-a:r-8845194847319360722&view=att&disp=safe&realattid=f_jona4yhn0>
[2] export GUIX_PACKAGE_PATH=~/my-guix; guix system reconfigure
/etc/config.scm -n :
with_spice_with_guix_package_path.log
(15K)
<https://mail.google.com/mail/u/0?ui=2&ik=f97d85874d&attid=0.2&permmsgid=msg-a:r-8845194847319360722&view=att&disp=safe&realattid=f_jonahgv11>

I think the two should give the same output. But as you see, those are
different. First, [1] does not have commented lines:
;;; note: source file /root/my-guix/gnu/packages/spice.scm
;;;       newer than compiled
/gnu/store/k7lvym1xl87p156jd459k36ddbb1msvm-guix-a7b7d48cc-modules/gnu/packages/spice.go
;;; note: source file /root/my-guix/gnu/packages/spice.scm
;;;       newer than compiled
/run/current-system/profile/lib/guile/2.2/site-ccache/gnu/packages/spice.go

And derivations to be built and packages to be downloaded are different.
But the same test for 'guix build' is positive.
build_with_spice_with_loadpath.log
(2K)
<https://mail.google.com/mail/u/0?ui=2&ik=f97d85874d&attid=0.4&permmsgid=msg-a:r-8845194847319360722&view=att&disp=safe&realattid=f_jonatz6i3>
build_with_spice_with_guix_package_path.log
(2K)
<https://mail.google.com/mail/u/0?ui=2&ik=f97d85874d&attid=0.3&permmsgid=msg-a:r-8845194847319360722&view=att&disp=safe&realattid=f_jonatz612>

Finally, I have real build run's.
[3] guix system reconfigure /etc/conf.scm -L ~/my-guix :
real_with_spice_with_loadpath.log
(10K)
<https://mail.google.com/mail/u/0?ui=2&ik=f97d85874d&attid=0.6&permmsgid=msg-a:r-8845194847319360722&view=att&disp=safe&realattid=f_jonazfpr5>

[4] export GUIX_PACKAGE_PATH=~/my-guix; guix system reconfigure
/etc/config.scm
real_with_spice_with_guix_package_path.log
(12K)
<https://mail.google.com/mail/u/0?ui=2&ik=f97d85874d&attid=0.5&permmsgid=msg-a:r-8845194847319360722&view=att&disp=safe&realattid=f_jonazfpe4>

Run [3] does not build spice-vdagent, but just grub.cfg. Run [4] does what
I want. Only [4] makes change in
/run/current-system/profile/etc/xdg/autostart/spice-vdagent.desktop .


Regards,

Taegil