Nixpkgs: zlib headers are not linked in ~/.nix-profile/include.

[kindaro]

Issue description

I wanted to build from source digest, a Haskell package that depends on the usual zlib system library. I used cabal executable installed via nix-env _(from cabal-install package)_. I also installed zlib in the same fashion, which made the headers and binary library objects available somewhere in /nix/store.

As advised in NixOS wiki, I set export CPATH=~/.nix-profile/include; export LIBRARY_PATH=~/.nix-profile/lib, but nevertheless cabal errored out:

% cd ~/code/haskell-src/digest
% cabal new-build
Build profile: -w ghc-8.2.2 -O1
In order, the following will be built (use -v for more details):
 - digest-0.0.1.2 (lib:digest) (configuration changed)
Configuring digest-0.0.1.2...
cabal: Missing dependency on a foreign library:
* Missing (or bad) header file: zlib.h
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.

I dug in and discovered that there is no directory ~/.nix-profile/include at all. I created it and manually simlinked zlib headers in. _(To be specific, there are two headers in zlib: zlib.h & zconf.h, and I linked both of them.)_ It solved the problem.

I wonder if these headers could be put in place by default.

Steps to reproduce

Install ghc, cabal-install, zlib. Download the source for digest. Enter the digest source directory and say cabal new-build.

Technical details

• system: "x86_64-linux"
• host os: Linux 4.14.56-1-lts, Arch Linux, noversion
• multi-user?: yes
• sandbox: no
• version: nix-env (Nix) 2.0
• channels(root): "nixpkgs-18.09pre137268.63a865c403c"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixpkgs

[teto]

zlib is used by many libraries already without any problem. zlib library is a multioutput library (see the doc for more details) so your dependency should include zlib.dev :
$ nix-build -A zlib.dev ~/nixpkgs

As a general tip, you can install nix-locate via nix-env and then run nix-locate zlib.h to find the correct output.

[kindaro]

@teto There must be a misunderstanding. I am not defining a package or derivation myself. What I am doing is manually building stuff using cabal that happens to be installed via Nix. So I do not think your advices are applicable.

By the way, when I say nix-env --query --available '.*zlib.*', nothing similar to zlib.dev would appear.

Is there a particular reason to refrain from symlinking those files?

[matthewbauer]

You should be able to run this in a nix-shell:

nix-shell '<nixpkgs>' -A haskellPackages.digest

[FRidh]

dev outputs are not installed in a profile.

[vcunat]

The way things are designed, nix-env is suitable for set of programs to be used and nix-shell is a much better fit for "development environments" (getting headers, various env-vars set up, etc.)

[vcunat]

For Haskell in particular, I suppose you'd best start by trying what's in the manual: https://nixos.org/nixpkgs/manual/#how-to-create-a-development-environment

[kindaro]

@vcunat Thank you for clarifying. I think I was misled by the following passage from the NixOS wiki _(also linked to in my initial post)_:

With Nix, you can install the needed development tools into your profile (gcc-wrapper, gnumake), and the dependencies for the source you want to build (libpng, qt, ...). Once that done, set the environment variables (for gcc): CPATH=~/.nix-profile/include; LIBRARY_PATH=~/.nix-profile/lib; QTDIR=~/nix-profile... And then you should get your build running.

From reading this section, I had had the impression that I could install zlib and cabal, set the environment variables as advised and everything will be prepared for building things. _(Otherwise, what is the point of setting the environment variable CPATH?)_ I do not think this problem is specific to Haskell, since the headers missing are C headers from zlib _(and not, for example, ghc's type checker's output)_ and the error is reported by ld _(and Cabal faithfully passes it to the terminal if set to be verbose)_. In fact, Haskell packages that do not require C libraries build just fine with this set-up.

So, is it possible that there is inconsistency between what is written in the wiki and what is actually happening?

[vcunat]

Yeah, that wiki page is misleading. It should also mention steam-run (a FHS-compatible env via Linux mount namespaces).

[stale[bot]]

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