I'm developing a Haskell program using Cabal in a nix-shell. I would like to have as many dependencies of the build installed by Nix as possible.
The simple.cabal file seems fairly standard (it was initially produced by stack). The full contents are here: https://pastebin.com/3wd8j0pp The only place alex and happy appear in the .cabal file are in the build-tool-depends sections.
I tried to keep the shell.nix file as simple as possible (but I'm also inexperienced in Nix):
{ pkgs ? import <nixpkgs> {}}:
let
ghc = pkgs.haskellPackages.ghcWithPackages (p:[
p.array
p.base
p.bound
p.containers
p.deriving-compat
p.haskeline
p.logict
p.mtl
p.text
p.unification-fd
p.alex
p.happy
p.BNFC
p.cabal-install
]);
alex = pkgs.haskellPackages.alex;
happy = pkgs.haskellPackages.happy;
in
pkgs.mkShell {
buildInputs = [ ghc pkgs.haskellPackages.alex pkgs.haskellPackages.happy pkgs.pkg-config];
buildTools = [ pkgs.haskellPackages.alex pkgs.haskellPackages.happy];
buildToolDepends = [pkgs.haskellPackages.alex pkgs.haskellPackages.happy];
ALEX="${alex}/bin/alex";
HAPPY="${happy}/bin/happy";
}
I saved environment variables to reference the locations of alex and happy.
Finally, I tried to tell cabal where to find alex and happy by specifying them in the extra-prog-path section of a cabal.project file. However, that didn't work, so I tried hard-coding in their location
packages: simple.cabal
extra-prog-path:
/nix/store/PATH-TO-ALEX/bin/alex
/nix/store/PATH-TO-HAPPY/bin/happy
Finally, on building to enter the nix-shell, nix-shell --pure shell.nix and then cabal build
The cabal tool build finds all the ghc library packages installed with ghcWithPackages correctly -- it requires none of them to be built. However, it seems to not know about alex nor happy. The output looks like this.
In order, the following will be built (use -v for more details):
- alex-3.2.6 (exe:alex) (requires build)
- happy-1.20.0 (exe:happy) (requires build)
I can also confirm that the version of alex and happy in the nix store are alex-3.2.6 and happy-1.20.0.
On the other hand, cabal v1-build does pick up alex and happy as installed. cabal v1-build
Resolving dependencies...
Configuring simple-0.1.0.0...
Preprocessing library for simple-0.1.0.0..
Building library for simple-0.1.0.0..
and the build completes successfully only compiling the source files in the local package.
It seems like one should favor v2-build or new-build. How can I get cabal to know where to find and also to use the alex and happy versions installed by Nix, or alternatively how to tell Nix what to do so that v2-build or new-build can find alex and happy?
