Difference between nix-build and nix-shell environments

Hi all!

I’ve stumbled into a particularly tricky issue when building a package in Nix. The package in question builds a Nim lang library with lots of dependencies. Along the way, Nim compiler invokes clang and provides header search paths to it.

When doing nix-build, the build fails with a message that a particular header cannot be found, and dumps the compiler invocation. It is clear that the header is there because the relevant header search path is included (it belongs to another Nix package). What is strange is that if i enter nix-shell and run genericBuild, it all works fine.

What could possibly cause this? Tried to compare environment variables between nix-build and nix-shell, everything is identical, except for unrelated stuff. I’m completely confused. Will be super-grateful for any pointers.

Intriguing. Can you post the default.nix file so someone can reproduce this locally and maybe help you figure out what’s going on?

Thanks for your response @roni ! Just to add more context, i’ve posted this same issue to Reddit channel https://www.reddit.com/r/NixOS/comments/m5gqtc/difference_between_nixbuild_and_nixshell/, and as it turned out, it seems that source $stdenv/setup is what breaks things. Meaning, if i enter nix-shell and run genericBuild, it’s ok, but if i do source $stdenv/setup before running genericBuild, it cannot find the header anymore!

Also, this might only affect macOS - i’ve asked my colleague to run this on Linux (NixOS actually), and it built just fine.

This is the actual code: https://github.com/status-im/nim-status/tree/feat/nix-build. In order to reproduce the problem, run nix-build --pure --attr targets.main.nim-status.host from within parent source directory. This will run the derivation in nix/nim-status/nim-status.nix.

So right now i’m trying to figure out what’s the problem by looking at stdenv-darwin/setup script.

I’m glad you’re making some progress. I’m sorry I can’t help further, as I don’t run any MacOS boxes. Good luck!