bug#33892: guix package --list-generations uses UTC and time-at-midnight for hour durations

[pelzflorian (Florian Pelz)]

Hello Guix,

I would expect guix package --list-generations=…h to display
generations from the past … hours, but apparently it displays
generations offset from UTC midnight (apparently not local time?) and
not the current time, since guix/ui.scm calls a procedure named
time-at-midnight.

In particular, when `guix package --list-generations` shows

Generation 38   Dec 15 2018 13:04:16    (current)

then I would expect

$ date --date="Dec 15 2018 13:04:16" +%s
1544875456
$ date +%s
1545989113
$ guix package --list-generations=$(((1545989113-1544875456)/3600+1))h

to display the current generation.

I think either the time for hours should not be computed from midnight
and should use local time for days/weeks.  Alternatively, the
description in the manual should be adjusted.

Regards,
Florian