This is a bug with provides() (srcpac ignores them) and ATM I've no idea on how to fix it :(

The following commands create an associative array called 'provides', indexed by package names. The values are either the version of the provided package or 'yes' if no version is explicitly specified in pacman's output.

$ declare -A provides
$ eval $(for i in $(LC_ALL=C pacman -Qi | grep Provides | grep -v None | cut -d: -f2); do echo $i | awk -F = '{print "provides[" $1 "]=" ($2 == "" ? "yes" : $2);}'; done)

After running the two lines above, the array seems to contain the expected data:

$ echo ${provides[x-server]}
yes
$ echo ${provides[libv4l]}
0.8.5

Once you have this array, srcpac could consult it before trying to build package dependencies (if required by -bb or -bbb, of course) and thus avoid the cyclic build attempts.

Unfortunately, this suggestion has an obvious problem: it only works in bash. AFAIK, some other popular shells, such as dash, do not implement associative arrays. (Such a feature might be non-standard.) But still, adding #!/bin/bash and using the associative array would be a nice temporary solution. :-)

Ooops, the array also contains some garbage... This happens because too many lines pass through the two greps. Adding a ^ might help:

$ declare -A provides
$ eval $(for i in $(LC_ALL=C pacman -Qi | grep '^Provides' | grep -v None | cut -d: -f2); do echo $i | awk -F = '{print "provides[" $1 "]=" ($2 == "" ? "yes" : $2);}'; done)

Now the array should be valid.

Nice to see some help ;)

Unfortunately I guess I cannot work on it soon.