noisy union-build

[Ricardo Wurmus]

Hi Guix,

whenever I build a new profile generation I see a lot of noise like
this:

~~~~~~~~~~~~~~~
...
`/gnu/store/k3r21zq5nrrkdp303vlw1cc2mrhhcl7b-ibus-1.5.11/share/icons/hicolor/scalable/apps/ibus-setup.svg'
 ~> 
`/gnu/store/z6na5mb36gqr0m018ci2ji9y4qkgjnbr-gtk-icon-themes/share/icons/hicolor/scalable/apps/ibus-setup.svg'
`/gnu/store/d6i21sw7nq7cdabp9k6k9y3mrl67lbbp-emacs-24.5/share/icons/hicolor/scalable/apps/emacs.svg'
 ~> 
`/gnu/store/z6na5mb36gqr0m018ci2ji9y4qkgjnbr-gtk-icon-themes/share/icons/hicolor/scalable/apps/emacs.svg'
`/gnu/store/k3r21zq5nrrkdp303vlw1cc2mrhhcl7b-ibus-1.5.11/share/icons/hicolor/scalable/apps/ibus.svg'
 ~> 
`/gnu/store/z6na5mb36gqr0m018ci2ji9y4qkgjnbr-gtk-icon-themes/share/icons/hicolor/scalable/apps/ibus.svg'
`/gnu/store/i7x10knncm1b7r3202dsijsqrqvq1s6p-geda-gaf-1.8.2/share/icons/hicolor/scalable/apps/geda-gattrib.svg'
 ~> 
`/gnu/store/z6na5mb36gqr0m018ci2ji9y4qkgjnbr-gtk-icon-themes/share/icons/hicolor/scalable/apps/geda-gattrib.svg'
`/gnu/store/i7x10knncm1b7r3202dsijsqrqvq1s6p-geda-gaf-1.8.2/share/icons/hicolor/scalable/apps/geda-gschem.svg'
 ~> 
`/gnu/store/z6na5mb36gqr0m018ci2ji9y4qkgjnbr-gtk-icon-themes/share/icons/hicolor/scalable/apps/geda-gschem.svg'
...
~~~~~~~~~~~~~~~

This is produced by the local ‘symlink*’ procedure inside of the
‘union-build’ procedure in ‘guix/build/union.scm’.

Could we please show all of this only upon request, e.g. when running in
verbose mode or by producing a profile log file or something?  In my
case these are more than 800 lines with information that I probably
don’t need to know about.

To a lesser degree this also applies to repeated messages like:

    gtk-update-icon-cache: Cache file created successfully.

as well as these messages (because as a user I cannot do anything about them):

    install-info: warning: no info dir entry in 
`/gnu/store/q9yx6mz6zw0z4hfivqb5pba8xpf3bx0a-lilypond-2.19.27/share/info/music-glossary.info.gz'

and finally the verbose and unsighty collision warnings:

    warning: collision encountered: 
/gnu/store/z6na5mb36gqr0m018ci2ji9y4qkgjnbr-gtk-icon-themes/share/icons/HighContrast/icon-theme.cache
 
/gnu/store/xjbvns4ammyxcijzg8q094xbbww6wic0-dconf-0.22.0/share/icons/HighContrast/icon-theme.cache
 
/gnu/store/fh6kwdjhxmvfc5xvs4zqawinaggy70r0-gnome-themes-standard-3.16.2/share/icons/HighContrast/icon-theme.cache
 
warning: arbitrarily choosing 
/gnu/store/z6na5mb36gqr0m018ci2ji9y4qkgjnbr-gtk-icon-themes/share/icons/HighContrast/icon-theme.cache

I wouldn’t mind the collision warnings so much if they were a little
prettier, even at the expense of using up more vertical space.

What do you think?

~~ Ricardo