trouble installing gtksourceview3

[David Naumann]

I've been using macports for years without trouble but I am having trouble installing gtksourceview3.   Any help appreciated.

My platform is up to date:
macOS 10.15.6
port 2.6.3 
After initial trouble with this port, I cleaned up and re-installed all my other ports, as follows:
   sudo port -fp uninstall --follow-dependents installed 
   sudo port install coreutils gnupg2 emacs-app python38 rcs opam swi-prolog libxml2 pkgconfig
All worked fine.  
But this fails:

>sudo port install gtksourceview3 +quartz 
Error: Unable to execute port: couldn't open "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_gnome_gtksourceview3/gtksourceview3/work/.macports.gtksourceview3.state": permission denied

Yet the file exists:
>ls -l /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_gnome_gtksourceview3/gtksourceview3/work/.macports.gtksourceview3.state 
-rw-r--r--  1 root  wheel  216 Aug  3 17:31 /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_gnome_gtksourceview3/gtksourceview3/work/.macports.gtksourceview3.state

Note that I don't have a macports user; all my other ports are successfully installing under root.  

Is it safe to just delete everything under build/ and try again?