There seems to be a file conflict between the packages
man-pages and
lapack-doc.
Running
pacman -Syu fails on my system, with the following message.
error: failed to commit transaction (conflicting files)
lapack-doc: /usr/share/man/man3/isnan.3.gz exists in filesystem (owned by man-pages)
Errors occurred, no packages were upgraded.
I have not done anything to change the default location of the files in these packages, so I suspect others can reproduce the problem by trying to install the two packages mentioned.