Arch Linux

It does list here:

[karol@black ~]$ pacman -S tumbler
resolving dependencies...
looking for inter-conflicts...

Targets (1): tumbler-0.1.21-3 [0,09 MB]

Total Download Size: 0,09 MB
Total Installed Size: 0,76 MB

Proceed with installation? [Y/n]
:: Retrieving packages from extra...
tumbler-0.1.21-3-i686 94,6K 367,4K/s 00:00:00 [################################] 100%
(1/1) checking package integrity [################################] 100%
(1/1) checking for file conflicts [################################] 100%
(1/1) checking available disk space [################################] 100%
(1/1) installing tumbler [################################] 100%
Optional dependencies for tumbler
ffmpegthumbnailer: for video thunbnails


Reporter's mirror may be out of date, as in  FS#25846 .

Hmmm...? (x86_64, today's sync)

ach ~ # pacman -Rns ffmpegthumbnailer
checking dependencies...

Remove (4): ffmpegthumbnailer-2.0.6-1 ffmpeg-20110724-1 rtmpdump-2.4-1
libva-1.0.14-1

Total Removed Size: 23.37 MB

Do you want to remove these packages? [Y/n]
(1/4) removing ffmpegthumbnailer [######################] 100%
(2/4) removing ffmpeg [######################] 100%
(3/4) removing rtmpdump [######################] 100%
(4/4) removing libva [######################] 100%
rch ~ # pacman -S tumbler
warning: tumbler-0.1.21-3 is up to date -- reinstalling
resolving dependencies...
looking for inter-conflicts...

Targets (1): tumbler-0.1.21-3

Total Download Size: 0.00 MB
Total Installed Size: 0.79 MB

Proceed with installation? [Y/n]
(1/1) checking package integrity [######################] 100%
(1/1) checking for file conflicts [######################] 100%
(1/1) upgrading tumbler [######################] 100%
rch ~ #

Note, that I have `x86_64'.

True, you don't get that info when reinstalling.

Try to remove it and install back.

Yes, that's the problem.
Anyway: Can we get it for installing no matter if it's a new install or reinstallation?

Isn't 'pacman -Qi tumbler' enough? It lists - among other things - optional depts:
[karol@black ~]$ sp -Qi tumbler | grep "Optional Deps"
Optional Deps : ffmpegthumbnailer: for video thunbnails

Well I think that could be a more general problem:
Imagine that I install thunar as a part of XFCE4. It uses an optional dependency: thunar-thumbnailers. After some time it gets obsoleted and the `tumbler' is recommended for this purpose. Of course: for fresh thunar install I'll get the message about a new dependency. But if I have XFCE4 and thunar as a part of it (no fresh install but reinstallation possible) I'll miss this dependency change (unless I check 'pacman -Qi' results on all installed packages...)?

May I suggest closing this bug (not a bug in fact, sorry!) and opening some feature request for pacman: printing this info after every `pacman -S something' no matter if yet installed or not?