How to handle gobject-2.0-0 and other library headers

Guides
1

For example, a python project with weasyprint will fail under nix with a message like:

OSError: cannot load library 'gobject-2.0-0': gobject-2.0-0: cannot open shared object file: No such file or directory.  Additionally, ctypes.util.find_library() did not manage to locate a library called 'gobject-2.0-0'

There might be a proper way, but for a quick n’ dirty solution,
enter a nix repl with the package list loaded:

nix repl --expr 'import <nixpkgs>{}'

find the desired package by writing it’s name. it auto-completes with a tab

nix-repl> glib
«derivation /nix/store/mwnrirg6ms58v7slply6aahgvj43ysrv-glib-2.76.2.drv»

nix-repl> glib.
glib.DETERMINISTIC_BUILD          glib.depsHostHostPropagated       glib.meta                         glib.postPatch
glib.NIX_CFLAGS_COMPILE           glib.depsTargetTarget             glib.mkHardcodeGsettingsPatch     glib.preCheck
<truncated>

Usually, out.outPath is what you want.

nix-repl> glib.out.outPath + "/lib"
"/nix/store/kaq6wabyc6bgj71ryv4wk7nb824h9kih-glib-2.76.2/lib"

we can check if this is the one by cd’ing into it and looking around

$ tree /nix/store/kaq6wabyc6bgj71ryv4wk7nb824h9kih-glib-2.76.2/
/nix/store/kaq6wabyc6bgj71ryv4wk7nb824h9kih-glib-2.76.2/
├── lib
│   ├── gio
│   │   └── modules
│   ├── glib-2.0
│   │   └── include
│   │       └── glibconfig.h
│   ├── libgio-2.0.so -> libgio-2.0.so.0
│   ├── libgio-2.0.so.0 -> libgio-2.0.so.0.7600.2
│   ├── libgio-2.0.so.0.7600.2
│   ├── libglib-2.0.so -> libglib-2.0.so.0
│   ├── libglib-2.0.so.0 -> libglib-2.0.so.0.7600.2
│   ├── libglib-2.0.so.0.7600.2
│   ├── libgmodule-2.0.so -> libgmodule-2.0.so.0
│   ├── libgmodule-2.0.so.0 -> libgmodule-2.0.so.0.7600.2
│   ├── libgmodule-2.0.so.0.7600.2
│   ├── libgobject-2.0.so -> libgobject-2.0.so.0
│   ├── libgobject-2.0.so.0 -> libgobject-2.0.so.0.7600.2
│   ├── libgobject-2.0.so.0.7600.2
│   ├── libgthread-2.0.so -> libgthread-2.0.so.0
│   ├── libgthread-2.0.so.0 -> libgthread-2.0.so.0.7600.2
│   └── libgthread-2.0.so.0.7600.2
├── libexec
│   └── gio-launch-desktop
└── share

line libgobject-2.0.so -> libgobject-2.0.so.0 tells us that this is the right nix expression.

then, in shell.nix, add the environment variable:

export LD_LIBRARY_PATH="${glib.out}/lib"

enter the nix-shell and gobject-2.0-0 should be accessible and you’re free of complaints.

This works for other packages too, but, i heave a feeling that nix must do this for us.
Honestly I wish there was a better (quicker) way to fix these problems.

2

The proper way of fixing packages using dlopen() or other similar functions (ctypes.util.find_library() in this case) is patching the code:

Using LD_LIBRARY_PATH is discouraged because environment variables are inherited by child processes and LD_LIBRARY_PATH takes precedence over DT_RUNPATH entry stored in ELF programs. As a result, if the program launches a different program, which depends on the library you are adding through LD_LIBRARY_PATH, and you are not careful about using the same build of the library as the one the child program was linked against, you might get ABI breakage.

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