PacmanBugs
From FrugalWiki
Debugging a database bug
A common problem is the following:
"pacman says no package has been installed!"
This is probably because your local database is broken. Don't worry, probably only there is a problem with one package.
$ echo n |sudo pacman -S glibc --debug=-1 |grep 'No such file' error: /var/lib/pacman/local/mplayer-1.0pre7-12/desc (No such file or directory)
^ in this case the mplayer package's entry was broken. The way to fix this database error is:
rm -rf /var/lib/pacman/local/mplayer-1.0pre7-12/
then
sudo pacman -Sf mplayer
For developers
If you got a broken pacman database, then you need something like this:
$ echo n |sudo pacman -S glibc -b `pwd`/pacman/ --debug=-1 |grep 'No such file' error: //home/vmiklos/darcs/pacman/test/pacman//local/mplayer-1.0pre7-12/desc (No such file or directory)
Then you can tell the user which package's entry is broken.