stack --nix build complains about ghc version mismatch - haskell

Question

When building threepenny-gui on NixOS with stack --nix build, I got error saying I have the wrong version of ghc. Then I tried stack --nix setup, which doesn't run because bash is on an unexpected path on NixOS (that's expected, since the stack documentation only mentions stack --nix build not setup). What am I missing?
FYI, to deal with the zlib issues I have also added a shell.nix and default.nix per https://github.com/commercialhaskell/stack/issues/2130
EDIT: was able to build with the method suggested by mkkeankylej from the above link, i.e. editing ~/.stack/config.yaml and add zlib to buildInputs in shell.nix But I'd still like to know if there's a way to do it w/o falling back to nix-shell? It sounds like stack --nix build should work as long as the nix-shell method does.

Answer 1

First of all, threepenny-gui seems to provide no stack.yaml, i.e. the project isn't configured to be built with stack. Thus, I wonder why you even bother using stack since that is not going to be any easier than building the project with cabal-install or even Nix directly. The easiest and fastest way is probably to configure the build by running:
$ nix-shell "<nixpkgs>" -A haskellPackages.threepenny-gui.env --run "cabal configure"
Afterwards, you can simply "cabal build" the project and work with it (inside or outside of a nix-shell) as you please; the compiler and all necessary build dependencies are provided by Nix.
If you don't want that, then you can use the normal cabal-install approach:
$ cabal sandbox init
$ cabal install --only-dependencies
$ cabal configure
$ cabal build
That build is probably going to require system libraries, like libz, so you must make sure that those are available. There's a million different ways to accomplish that, but the cleanest IMHO is the following:
$ zlibinc=$(nix-build --no-out-link "<nixpkgs>" -A zlib.dev)
$ zliblib=$(nix-build --no-out-link "<nixpkgs>" -A zlib.out)
$ cabal install --only-dependencies --extra-include-dirs=$zlibinc --extra-lib-dirs=$zliblib
Last but not least, it's not obvious to me why your stack build --nix command won't succeed, because that command will use Nix to install the proper version of GHC automatically. So if that doesn't work, then my best guess is that you're using an old version of stack where that feature doesn't work properly. I've tried that build using the stack binary that Nix provides, stack 1.3.2, and it can compile a current git checkout of threepenny-gui just fine:
$ git clone git://github.com/HeinrichApfelmus/threepenny-gui.git
Cloning into 'threepenny-gui'...
remote: Counting objects: 4102, done.
remote: Total 4102 (delta 0), reused 0 (delta 0), pack-reused 4101
Receiving objects: 100% (4102/4102), 1.88 MiB | 581.00 KiB/s, done.
Resolving deltas: 100% (2290/2290), done.
$ cd threepenny-gui
$ stack init
Looking for .cabal or package.yaml files to use to init the project.
Using cabal packages:
- threepenny-gui.cabal
Selecting the best among 9 snapshots...
* Partially matches lts-7.16
websockets-snap not found
- threepenny-gui requires >=0.8 && <0.11
Using package flags:
- threepenny-gui: buildexamples = False, network-uri = True, rebug = False
* Matches nightly-2017-01-17
Selected resolver: nightly-2017-01-17
Initialising configuration using resolver: nightly-2017-01-17
Total number of user packages considered: 1
Writing configuration to file: stack.yaml
All done.
$ stack build --nix --nix-packages zlib
threepenny-gui-0.7.1.0: configure (lib)
Configuring threepenny-gui-0.7.1.0...
threepenny-gui-0.7.1.0: build (lib)
Preprocessing library threepenny-gui-0.7.1.0...
[...]
Registering threepenny-gui-0.7.1.0...
This works without any specially edited config files for nix-shell, nor does it require special customization of stack.