How do I supply a C library to stack on NixOS? - haskell

Question

I have a stack-based project that depends on a couple C libraries. One of these C libraries, zlib, is available from a native NixOS package and I can put into the nix section of stack.yaml:
nix:
enable: true
packages:
- "zlib"
The other is not part of nixpkgs. The stack documentation suggests that the alternative to using the nix section in stack.yaml is to "write a shell.nix" without elaborating much.
So I wrote one, sticking to zlib as an example:
{ pkgs ? import <nixpkgs> { } }:
pkgs.mkShell {
buildInputs = [
pkgs.pkgconfig
pkgs.zlib
pkgs.stack
];
}
This gives me a working pkg-config for zlib:
[nix-shell:~/Work/PrivateStorage/PaymentServer]$ pkg-config --modversion zlib
1.2.11
However, it doesn't appear to make stack able to find the library:
[nix-shell:~/Work/PrivateStorage/PaymentServer]$ stack build
zlib-0.6.2: configure
Progress 1/7
-- While building package zlib-0.6.2 using:
/home/exarkun/.stack/setup-exe-cache/x86_64-linux-nix/Cabal-simple_mPHDZzAJ_2.4.0.1_ghc-8.6.5 --builddir=.stack-work/dist/x86_64-linux-nix/Cabal-2.4.0.1 configure --with-ghc=/nix/store/zfpm9bai9gj8vs09s2i2gkhvgsjkx13z-ghc-8.6.5/bin/ghc --with-ghc-pkg=/nix/store/zfpm9bai9gj8vs09s2i2gkhvgsjkx13z-ghc-8.6.5/bin/ghc-pkg --user --package-db=clear --package-db=global --package-db=/home/exarkun/.stack/snapshots/x86_64-linux-nix/lts-14.1/8.6.5/pkgdb --libdir=/home/exarkun/.stack/snapshots/x86_64-linux-nix/lts-14.1/8.6.5/lib --bindir=/home/exarkun/.stack/snapshots/x86_64-linux-nix/lts-14.1/8.6.5/bin --datadir=/home/exarkun/.stack/snapshots/x86_64-linux-nix/lts-14.1/8.6.5/share --libexecdir=/home/exarkun/.stack/snapshots/x86_64-linux-nix/lts-14.1/8.6.5/libexec --sysconfdir=/home/exarkun/.stack/snapshots/x86_64-linux-nix/lts-14.1/8.6.5/etc --docdir=/home/exarkun/.stack/snapshots/x86_64-linux-nix/lts-14.1/8.6.5/doc/zlib-0.6.2 --htmldir=/home/exarkun/.stack/snapshots/x86_64-linux-nix/lts-14.1/8.6.5/doc/zlib-0.6.2 --haddockdir=/home/exarkun/.stack/snapshots/x86_64-linux-nix/lts-14.1/8.6.5/doc/zlib-0.6.2 --dependency=base=base-4.12.0.0 --dependency=bytestring=bytestring-0.10.8.2 --extra-include-dirs=/nix/store/a54skdf3xksiqvcvr75bjpdl1jx8dgbk-gmp-6.1.2-dev/include --extra-include-dirs=/nix/store/br7kq0kvbn73rhzl17js0w3pprphhzv1-git-2.19.2/include --extra-include-dirs=/nix/store/ghzg4kg0sjif58smj2lfm2bdvjwim85y-gcc-wrapper-7.4.0/include --extra-include-dirs=/nix/store/zfpm9bai9gj8vs09s2i2gkhvgsjkx13z-ghc-8.6.5/include --extra-lib-dirs=/nix/store/br7kq0kvbn73rhzl17js0w3pprphhzv1-git-2.19.2/lib --extra-lib-dirs=/nix/store/ghzg4kg0sjif58smj2lfm2bdvjwim85y-gcc-wrapper-7.4.0/lib --extra-lib-dirs=/nix/store/kggcrzpa5hd41b7v60wa7xjkgjs43xsl-gmp-6.1.2/lib --extra-lib-dirs=/nix/store/zfpm9bai9gj8vs09s2i2gkhvgsjkx13z-ghc-8.6.5/lib
Process exited with code: ExitFailure 1
Logs have been written to: /home/exarkun/Work/PrivateStorage/PaymentServer/.stack-work/logs/zlib-0.6.2.log
Configuring zlib-0.6.2...
Cabal-simple_mPHDZzAJ_2.4.0.1_ghc-8.6.5: Missing dependency on a foreign
library:
* Missing (or bad) header file: zlib.h
* Missing (or bad) C library: z
This problem can usually be solved by installing the system package that
provides this library (you may need the "-dev" version). If the library is
already installed but in a non-standard location then you can use the flags
--extra-include-dirs= and --extra-lib-dirs= to specify where it is.If the
library file does exist, it may contain errors that are caught by the C
compiler at the preprocessing stage. In this case you can re-run configure
with the verbosity flag -v3 to see the error messages.
If the header file does exist, it may contain errors that are caught by the C
compiler at the preprocessing stage. In this case you can re-run configure
with the verbosity flag -v3 to see the error messages.
For zlib, there's no particular need to go this route, but as far as I can tell, I cannot put my non-nixpkgs package into the nix.packages list in stack.yaml.
How do I get stack to find these libraries?

Answer 1

Apparently a case of end-of-the-day documentation-reading-fail. This morning, it didn't take long to find the stack documentation that explains how to use a custom shell.nix. The stack docs do elaborate on how this works, including an example which shows it's not at all like the shell I thought was expected:
{ghc}:
with (import <nixpkgs> {});
haskell.lib.buildStackProject {
inherit ghc;
name = "myEnv";
buildInputs = [ glpk pcre ];
}
Adapting my shell to use buildStackProject instead of mkShell:
{ ghc }:
with (import <nixpkgs> { overlays = [ (import ./overlay.nix) ]; });
haskell.lib.buildStackProject {
inherit ghc;
name = "PrivacyPass";
# extra-library made available via the overlay.
# overlay probably not strictly necessary here, either.
buildInputs = [ zlib extra-library ];
}
and then pointing stack at it in stack.yaml:
nix:
enable: true
shell-file: "stack-shell.nix"
results in a successful build.