Comment (by Roland Haas):

There’s no real good way. There is a “version” attached with an ExternalLibrary but that does not give any guarantee about the version of the library actually used (in particular when using a system provided one and not building from source).

I have a bad way of testing for GSL in: https://github.com/rhaas80/RePrimAnd/commit/a8f5a6664739b676e1fb44208cae5a790e34e36a but is is kludgy since I basically do a mini autoconf.

Meson of course contains the correct version dependency but for the ET build I am not using Meson (too many dependencies on Python).

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2610/reprimand-thorn-requires-gsl-20-but-does