How create a nix package with haskell stack - haskell

Question

I need to create the nix package from a project stack with postgres template.
Basically it is the following: I have a virtual machine with NixOS and I need to portlet my project to another one with NixOS. For this I will use the nix copy command, but before I need to somehow "install" my project so that it is in /nix/store.
I tried to do the same looking at another issue posted "Generating a Nix package from a stack project".
come on. What I did was:
cd /home/ProjetoApp
stack new TesteYesod yesod-postgres
cd TestYesod
stack init --resolver lts-11.22
stack install yesod-bin --install-ghc
I added in stack.yaml:
nix
pure: true
enable: true
packages: [postgresql]
So far so good. I can compile and execute only stack. Then I was trying to generate a nix package. In stack.yaml I did:
nix
pure: true
enable: true
shell-file: default.nix
And in default.nix I did:
{nixpkgs ? import <nixpkgs> { }, ghc ? nixpkgs.ghc}:
with nixpkgs;
haskell.lib.buildStackProject {
name ="teste-yesod-1.0.0";
src = ./.;
buildInputs = [ postgresql ];
inherit ghc;
}
If I do:
nix build
Occurs:
builder for '/nix/store/rckhmkgrkb6nzn7dkqqldfdm8cilpya2-teste-yesod
1.0.0.drv' failed with exit code 1; last 5 log lines:
unpacking sources
unpacking source archive /nix/store/
n62hzn4igi1b7khksa6sp3cq8gk4h344-TesteYesod
source root is TestYesod
patching sources
configuring
[0 built (1 failed), 0.0 MiB DL]
error: build of '/nix/store/rckhmkgrkb6nzn7dkqqldfdm8cilpya2-teste-yesod-
1.0.0.drv' failed
If. How to instruct nix that the source is spread across multiple directories?

Answer 1

If you want a quick fix, the following should work:
{ nixpkgs ? import (builtins.fetchTarball {
url = "https://github.com/NixOS/nixpkgs/archive/d42ef371c9b1b532400b0f2820885e575f4f1617.tar.gz";
sha256 = "0irb4zb6hdgaah238244jk2xf63xfb20xy3plb1194pd4xbgdr3r";
}) {}
, ghc ? nixpkgs.ghc
}:
with nixpkgs;
haskell.lib.buildStackProject {
name ="TesteYesod";
src = ./.;
buildInputs = [ postgresql ];
inherit ghc;
}
What's the problem? It seems that in the current 18.09 release, buildStackProject is broken. The non-existent error message is caused by a subtly failing preConfigure script, which contains the following:
addStackArgsHook = ''
for pkg in ''${pkgsHostHost[#]} ''${pkgsHostBuild[#]} ''${pkgsHostTarget[#]}
do
[ -d "$pkg/lib" ] && \
export STACK_IN_NIX_EXTRA_ARGS+=" --extra-lib-dirs=$pkg/lib"
[ -d "$pkg/include" ] && \
export STACK_IN_NIX_EXTRA_ARGS+=" --extra-include-dirs=$pkg/include"
done
'';
In your case, stack is the last dependency to be processed in the loop (and perhaps in all buildStackProject invocations in 18.09, I'm not sure), but it contains no /lib or /include directory, so the exit code with which the preConfigure script exits is 1, and so the whole build process quits. This is just because of the shorthand &&, it would work if there was a proper if.
It is however fixed in master already (https://github.com/NixOS/nixpkgs/pull/53618), so simply using a newer nixpkgs should fix that problem. Pinning the nixpkgs is something you want to do anyway if you want to use Nix's replicability guarantees to the fullest, as you can't know you're using the same nixpkgs commit, so you may be using different versions of system packages.
(If you want to know how I debugged this - it seemed the problem was in the preConfigure step, so I took a look at the code in generic-stack-builder.nix, saw that preConfigure was overridable, copy-pasted the code from there into default.nix and added a set -x at the top. That showed me the problem above, and prompted me to go look at that file in master to see if there weren't changes since 18.09. Another workaround could be simply adding true to the preConfigure script if it wasn't already fixed in master, but that wasn't necessary.)
(Also, I've opened https://github.com/NixOS/nixpkgs/issues/55548 to backport the fix to 18.09.)