I'm also removing the pants13-pre attribute since it's unnecessary and I
don't want to maintain 1.4.x prereleases yet.
I'm temporarily taking out the pants native rust engine shenanigans until
I can get a nix-native rust build of it to work (it works on Linux but
not on Darwin!)
Third time's a charm. Not sure how I thought that three different files
would download and have the same hash, but that's what the old code did.
This one should have the three distinct platform hashes.
When transplanting the expression in 845d1b28bf
I accidentally switched pants 1.3 to use the old pathspec, which breaks
at runtime. This should fix it.
