tl;dr: The file is not a script, and comments need to be on their own line.
I ran into a problem updating my system, getting "URL rejected malformed input to a URL function" error. I researched all about mirrors and an apparent curl update that requires %20 for spaces, and such. None solved my problem, so I'm leaving this here.
Solved: what none of the websites addressed was "administrator brilliance". I decided that the pacman.conf file entry:
Architecture = auto
should be:
Architecture = x86_64 # uname -m
So the inline comment was messing up the pacman command.