"Cannot coerce null to a string" in buildMix

[lukateras]

@olcai wrote on Feb 7, 2019 2:44pm UTC:

Hi and thanks for this interesting project!

I just tried it out on two different Elixir projects, but I cannot get it work on either of them. After creating a default.nix just as described in the README and running nix-build I get the following output:

$ nix-build
error: cannot coerce null to a string, at /nix/store/nh38qpbmmrli8w3zqv00jv120chf1biz-nixos-18.09.1819.76aafbf4bf4/nixos/pkgs/development/beam-modules/build-mix.nix:32:13

I'm no Nix expert, but it seems that the issue is that name is not set when calling build-mix.nix. Does anyone have a good idea what could be wrong and how to fix it?

I'm running NixOS 18.09 on my end (although it seems to me that mix-to-nix is using a pinned version of nixpkgs).

[lukateras]

@olcai wrote on Feb 7, 2019 3:17pm UTC:

Of course I found the issue just a short while after writing this issue.

After following the code in greater detail I could easily see that I need to set the app name and version in mix.exs for it to work.

Perhaps a small comment about this could be added to the README so that others won't stumble as I just did.

Thank you and sorry for the noise!

[lukateras]

@yegortimoshenko wrote on Feb 7, 4:44pm UTC:

although it seems to me that mix-to-nix is using a pinned version of nixpkgs

pkgs.nix is used for CI and tests only, other than that Mix to Nix reuses user's <nixpkgs>.

Perhaps a small comment about this could be added to the README so that others won't stumble as I just did.

Sure! I thought that mix doesn't work on projects without name/version. Does it?

[lukateras]

@olcai wrote on Feb 7, 2019 8:34pm UTC:

Sure! I thought that mix doesn't work on projects without name/version. Does it?

Yes, you can leave these fields out. The issue in my case is that I have applications in an umbrella, and therefore I had no name or version in the top-level mix file.

[lukateras]

@yegortimoshenko wrote on Feb 7, 2019 8:41pm UTC:

In that case, Mix to Nix has to be fixed. Thanks for the report!