The entry for external libraries in the thornlist looks like this:

‌

# Additional Cactus thorns
!TARGET   = $ARR
!TYPE     = svn
!URL      = https://github.com/EinsteinToolkit/$1-$2.git/trunk

‌

this is a git repo, not an svn repo. So the entry should be

‌

# Additional Cactus thorns
!TARGET   = $ARR
!TYPE     = git
!URL      = https://github.com/EinsteinToolkit/$1-$2.git

I’m happy to submit a PR. But I wanted to report the bug first, since I might not get to it today. This appears to be present in both the development version and Proca.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2293/thornlists-entry-for-external-libraries-on