Fix nix build on OSX

[jmatsushita]

cryptobox and zauth wouldn't build on OSX because the wrong path was included in the dylib.

The symptom was that the cryptobox-c haskell library build would fail with:

cryptobox-haskell                > running .stack-work/dist/x86_64-osx-nix/Cabal-3.0.1.0/build/System/CryptoBox_hsc_make failed (exit code -6)
cryptobox-haskell                > rsp file was: ".stack-work/dist/x86_64-osx-nix/Cabal-3.0.1.0/build/System/hsc2hscall42850-3.rsp"           
cryptobox-haskell                > output file:".stack-work/dist/x86_64-osx-nix/Cabal-3.0.1.0/build/System/CryptoBox.hs"                      
cryptobox-haskell                > command was: .stack-work/dist/x86_64-osx-nix/Cabal-3.0.1.0/build/System/CryptoBox_hsc_make  >.stack-work/dist/x86_64-osx-nix/Cabal-3.0.1.0/build/System/CryptoBox.hs
cryptobox-haskell                > error: dyld: Library not loaded: /private/tmp/nix-build-cryptobox-c-2019-06-17.drv-0/source/target/x86_64-apple-darwin/release/deps/libcryptobox.dylib
cryptobox-haskell                >   Referenced from: /private/tmp/stack-3f8b56a5eca0af97/cryptobox-haskell-0.1.1/.stack-work/dist/x86_64-osx-nix/Cabal-3.0.1.0/build/System/CryptoBox_hsc_make
cryptobox-haskell                >   Reason: image not found

$ otool -l /nix/store/hzj1xl80qq3xg7fxd6l3adx0ahil3pyb-cryptobox-c-2019-06-17/lib/libcryptobox.dylib
...
Load command 3
          cmd LC_ID_DYLIB
      cmdsize 144
         name /private/tmp/nix-build-cryptobox-c-2019-06-17.drv-0/source/target/x86_64-apple-darwin/release/deps/libcryptobox.dylib (offset 24)
   time stamp 1 Thu Jan  1 01:00:01 1970
...

The fix proposed in this post fixed the problem.

$ otool -l /nix/store/w71z1pnxxx6wi69brl5pdzssdpa54yam-cryptobox-c-2019-06-17/lib/libcryptobox.dylib
...
Load command 3
          cmd LC_ID_DYLIB
      cmdsize 120
         name /nix/store/w71z1pnxxx6wi69brl5pdzssdpa54yam-cryptobox-c-2019-06-17/lib/libcryptobox.dylib (offset 24)
   time stamp 1 Thu Jan  1 01:00:01 1970
      current version 0.0.0
...

[akshaymankar]

Looks good to my noob eyes.

[jmatsushita]

Adding @lucendio as I heard you tried OSX Nix things before.

[arianvp]

and this was absolutely needed? I thought it fixed itself by just bumping nixpkgs no?

The fact that buildRustPackage outputs binaries with broken paths sounds like something we should report as a bug upstream.

[jmatsushita]

That was PBUK. Paths looked ok.... but not when I scrolled up. And it didn't build until I made that change.

It's a known issue apparently https://discourse.nixos.org/t/patchelf-for-mach-o-shared-libraries/562/6 there's even a hook for it fixDarwinDylibNames.

[lucendio]

Adding @lucendio as I heard you tried OSX Nix things before.

due to my lack of experience with nix and Haskell on macos (and in general), I'm not equipped to review and give feedback.

[jmatsushita]

All good @lucendio thanks!