Build warnings on MacOS ("non-portable path to file")

[brianhuffman]

Running make on MacOS yields a bunch of these warnings:

Building executable 'cryptol' for cryptol-2.5.0..

<built-in>:15:10: error:
     warning: non-portable path to file '"dist/build/Cryptol/autogen/cabal_macros.h"'; specified path differs in case from file name on disk [-Wnonportable-include-path]
#include "dist/build/cryptol/autogen/cabal_macros.h"
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         "dist/build/Cryptol/autogen/cabal_macros.h"
1 warning generated.

The problem is that cabal tries to create the directory dist/build/Cryptol for the compiled modules, and also the directory dist/build/cryptol for binaries. On MacOS, dist/build/cryptol maps onto the existing dist/build/Cryptol, because they only differ by case. I'm using cabal version 2.2.0.0.

Apparently this is a known issue with cabal: haskell/cabal#4739

Perhaps we should adopt one of the workarounds listed in that thread.

[atomb]

I believe that migrating to cabal new-build would get rid of this problem. The current build is somewhat tightly tied to sandboxes, so I'm reluctant to change this in time for 2.6.0, but after that I think it would be very worthwhile to start using new-build in the Makefile.

We're already successfully using new-build on Travis, but we're not using Travis to build distribution tarballs. I think the main remaining step for using new-build for distributions is locating the generated executables. They're deep in the dist-newstyle directory, and I don't think Cabal makes any promises that their locations won't change from release to release.

[brianhuffman]

Using cabal new-build or cabal v2-build seems to fix the problem. So I think this ticket is now subsumed by #570.