Comment (by Roland Haas):

This is not actually an error in the thorn list since the ExternalLibraries are intended to be downloaded via subversion.

You will have to install a subversion command to use, for example following the instructions in the new user tutorial: https://nbviewer.jupyter.org/github/nds-org/jupyter-et/blob/master/CactusTutorial.ipynb

OSX has gone back and forth between providing a usable svn client and not doing so.

Can you let me know which version of OSX and Xcode you are using, please?

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2390/build-failed-with-wrong-thornlist