On my system, I have both brew and port installed, and sometimes, I have libraries present in both of them. For example I have the gmp library installed in both of them, so when I install zarith, the detection will select the library from brew (my understanding is that brew is always checked first).
Is it possible to by-pass this and make opam select the library in port instead ? Maybe by setting or overriding manually os-distribution ? At the moment, I have to temporarily “hide” homebrew from opam while I install zarith to make it choose the right library.