# Nix-build fails, but using nix-shell + cabal etc. works
**URL:** https://discourse.nixos.org/t/nix-build-fails-but-using-nix-shell-cabal-etc-works/6894
**Category:** Help
**Created:** [April 25, 2020, 7:30pm UTC](https://discourse.nixos.org/t/nix-build-fails-but-using-nix-shell-cabal-etc-works/6894 "2020-04-25T19:30:01Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@mhwombat](https://discourse.nixos.org/u/mhwombat)
#### Post date: [April 25, 2020, 7:30pm UTC](https://discourse.nixos.org/t/nix-build-fails-but-using-nix-shell-cabal-etc-works/6894/1 "2020-04-25T19:30:01Z")
When I try building my project using `nix-build`, it fails. However, I can build it without any problems using `nix-shell` and cabal. So I have a way to build my project, but **I am curious why nix-build is failing here.** Could it be because I once accidentally ran cabal-update outside of a nix shell?
When I build using nix-build, it complains about missing dependencies: lens ==4.19.\*
```auto
$ nix-build release.nix
these derivations will be built:
/nix/store/5bppyi384lyf2x4anfafkam3fcx4cynv-creatur-wains-9.7.drv
building '/nix/store/5bppyi384lyf2x4anfafkam3fcx4cynv-creatur-wains-9.7.drv'...
setupCompilerEnvironmentPhase
Build with /nix/store/vrdzir6ql35x1an44ln0vir3a3pra75f-ghc-8.4.4.
unpacking sources
unpacking source archive /nix/store/w3qndrqryhff2a5yl7x1zh9mqbw6yrwj-creatur-wains
source root is creatur-wains
patching sources
compileBuildDriverPhase
setupCompileFlags: -package-db=/build/setup-package.conf.d -j16 -threaded
[1 of 1] Compiling Main ( Setup.hs, /build/Main.o )
Linking Setup ...
configuring
configureFlags: --verbose --prefix=/nix/store/vs6v0g2lw2p4gqx4gjyzkcaravmjm9zn-creatur-wains-9.7 --libdir=$prefix/lib/$compiler --libsubdir=$abi/$libname --docdir=/nix/store/dgkdbkiaj5f28xbk7gxsls01vj27n4vz-creatur-wains-9.7-doc/share/doc/creatur-wains-9.7 --with-gcc=gcc --package-db=/build/package.conf.d --ghc-option=-j16 --disable-split-objs --enable-library-profiling --profiling-detail=exported-functions --disable-profiling --enable-shared --disable-coverage --enable-static --disable-executable-dynamic --enable-tests --enable-library-vanilla --enable-library-for-ghci --ghc-option=-split-sections --extra-lib-dirs=/nix/store/9kr7pv6m220gk5518qvkbxdbwq5gzb80-ncurses-6.1-20181027/lib --extra-lib-dirs=/nix/store/rxaclc3vhxbzgfllv7601i85z854h48a-gmp-6.1.2/lib
Using Parsec parser
Configuring creatur-wains-9.7...
CallStack (from HasCallStack):
die', called at libraries/Cabal/Cabal/Distribution/Simple/Configure.hs:958:20 in Cabal-2.2.0.1:Distribution.Simple.Configure
configureFinalizedPackage, called at libraries/Cabal/Cabal/Distribution/Simple/Configure.hs:462:12 in Cabal-2.2.0.1:Distribution.Simple.Configure
configure, called at libraries/Cabal/Cabal/Distribution/Simple.hs:596:20 in Cabal-2.2.0.1:Distribution.Simple
confHook, called at libraries/Cabal/Cabal/Distribution/Simple/UserHooks.hs:67:5 in Cabal-2.2.0.1:Distribution.Simple.UserHooks
configureAction, called at libraries/Cabal/Cabal/Distribution/Simple.hs:178:19 in Cabal-2.2.0.1:Distribution.Simple
defaultMainHelper, called at libraries/Cabal/Cabal/Distribution/Simple.hs:115:27 in Cabal-2.2.0.1:Distribution.Simple
defaultMain, called at Setup.hs:2:8 in main:Main
Setup: Encountered missing dependencies:
lens ==4.19.*
builder for '/nix/store/5bppyi384lyf2x4anfafkam3fcx4cynv-creatur-wains-9.7.drv' failed with exit code 1
error: build of '/nix/store/5bppyi384lyf2x4anfafkam3fcx4cynv-creatur-wains-9.7.drv' failed
```
When I build using `nix-shell` and cabal, everything works, and there’s no problem finding a suitable version of `lens`.
```auto
$ nix-shell
. . .
(nix-shell) $ cabal configure
. . .
- lens-4.19.2 (requires download & build)
. . .
(nix-shell) $ cabal build
Build profile: -w ghc-8.4.4 -O1
In order, the following will be built (use -v for more details):
. . .
- lens-4.19.2 (lib:lens) (requires download & build)
. . .
Downloaded lens-4.19.2
. . .
Linking /home/amy/github/creatur-wains/dist-newstyle/build/x86_64-linux/ghc-8.4.4/creatur-wains-9.7/x/creatur-wains-teaching-test/build/creatur-wains-teaching-test/creatur-wains-teaching-test ...
(nix-shell) $ cabal test
Build profile: -w ghc-8.4.4 -O1
. . .
Running 1 test suites...
Test suite creatur-wains-test: RUNNING...
Test suite creatur-wains-test: PASS
Test suite logged to:
/home/amy/github/creatur-wains/dist-newstyle/build/x86_64-linux/ghc-8.4.4/creatur-wains-9.7/t/creatur-wains-test/test/creatur-wains-9.7-creatur-wains-test.log
1 of 1 test suites (1 of 1 test cases) passed.
```
Here are the relevant files.
```auto
$ cat shell.nix
(import ./release.nix).project.env
```
```auto
$ cat project.nix
{ mkDerivation, base, bytestring, cereal, containers, creatur
, deepseq, directory, filepath, lens, MonadRandom, mtl
, numeric-tools, QuickCheck, random, som, stdenv, test-framework
, test-framework-quickcheck2, unix
}:
mkDerivation {
pname = "creatur-wains";
version = "9.7";
src = ./.;
isLibrary = true;
isExecutable = true;
libraryHaskellDepends = [
base bytestring cereal containers creatur deepseq directory
filepath lens MonadRandom mtl random som unix
];
executableHaskellDepends = [
base cereal containers creatur deepseq lens MonadRandom mtl
QuickCheck random som test-framework test-framework-quickcheck2
];
testHaskellDepends = [
base cereal containers creatur deepseq lens MonadRandom mtl
numeric-tools QuickCheck random som test-framework
test-framework-quickcheck2
];
homepage = "https://github.com/mhwombat/creatur-wains#readme";
description = "Artificial agent specialised for for pattern discovery";
license = stdenv.lib.licenses.bsd3;
}
```
```auto
$ cat release.nix
let
config = {
packageOverrides = pkgs: rec {
haskellPackages = pkgs.haskellPackages.override {
overrides = haskellPackagesNew: haskellPackagesOld: rec {
project =
haskellPackagesNew.callPackage ./project.nix { };
creatur =
haskellPackagesNew.callPackage ./creatur.nix { };
som =
haskellPackagesNew.callPackage ./som.nix { };
grid =
haskellPackagesNew.callPackage ./grid.nix { };
gray-extended =
haskellPackagesNew.callPackage ./gray-extended.nix { };
};
};
};
};
pkgs = import { inherit config; };
in
{ project = pkgs.haskellPackages.callPackage ./project.nix { };
}
```
I can provide creatur.nix, gray-extended.nix, grid.nix and som.nix if anyone wants.
System info:
```auto
$ nix-shell -p nix-info --run "nix-info -m"
- system: `"x86_64-linux"`
- host os: `Linux 4.19.116, NixOS, 19.09.2431.cae3ac8c30b (Loris)`
- multi-user?: `yes`
- sandbox: `yes`
- version: `nix-env (Nix) 2.3.3`
- channels(amy): `"nixpkgs-18.09.1676.7e88992a8c7"`
- channels(root): `"nixos-19.09.2431.cae3ac8c30b"`
- nixpkgs: `/home/amy/.nix-defexpr/channels/nixpkgs`
```
---
### Author:  [@cdepillabout](https://discourse.nixos.org/u/cdepillabout)
#### Post date: [April 26, 2020, 5:01am UTC](https://discourse.nixos.org/t/nix-build-fails-but-using-nix-shell-cabal-etc-works/6894/2 "2020-04-26T05:01:39Z")
The problem you’re seeing is caused because nixpkgs only contains one version of a given dependency (in some cases multiple versions), but `cabal` knows about all versions of your dependencies and has a solver built-in to figure out which version to use.
For example, nixpkgs might only contain a derivation for `lens-4.18.0`. Since that doesn’t meet the version you require in `creatur-wains.cabal`, `nix-build` just fails.
However, when building with `cabal`, `cabal` looks on Hackage and sees that there is a `lens-4.19.0` (or whatever) available and downloads and uses that.
The easiest solution is to either relax the version bounds for the `lens` dependency in your `creatur-wains.cabal` file, or to override the nixpkgs version of `lens` in your `release.nix` file (with a function like `callHackage`).
* * *
This isn’t related to the problem you’re seeing above, but I’d also suggest you use the `callCabal2nix` function to build your own packages in your `release.nix` file, instead of generating the `creatur.nix`, etc files by hand with `cabal2nix` and using `callPackage` on them.
See [Nix Haskell Development (2020)](https://discourse.nixos.org/t/nix-haskell-development-2020/6170) for some more suggestions.
---
### Author:  [@mhwombat](https://discourse.nixos.org/u/mhwombat)
#### Post date: [April 26, 2020, 3:53pm UTC](https://discourse.nixos.org/t/nix-build-fails-but-using-nix-shell-cabal-etc-works/6894/3 "2020-04-26T15:53:01Z")
Thank you so much for the very clear explanation, and for the suggestions.