Nix crashes on conflicting home-manager options

[jakubkaczor]

Describe the bug

Nix crashes.

Context

I have the following home-manager Zellij configuration. I think this is not minimal configuration triggering the issue. I suppose zellij.enabled = true and following the Steps To Reproduce would be sufficient.

    zellij = {
      enable = true;
      enableZshIntegration = true;
    };
    nushell.extraConfig = ''
      if $env.ZELLIJ? == null {
        if $env.ZELLIJ_AUTO_ATTACH? == "true" {
          ${config.programs.zellij.package}/bin/zellij attach -c
        } else {
          ${config.programs.zellij.package}/bin/zellij
        }

        if $env.ZELLIJ_AUTO_EXIT? == "true" {
          exit
        }
      }
    '';

Steps To Reproduce

1. Set home.sessionVariables.ZELLIJ_AUTO_EXIT = "true"; in home-manager configuration.
2. Home-manager switch.

Expected behavior

Nix not crashing, but simply reporting an error message.

Metadata

> nix-env --version
nix-env (Nix) 2.28.5

Checklist

• checked [latest Nix manual] ([source])
• checked [open bug issues and pull requests] for possible duplicates

---

I was asked in the stdout to report a bug and include the following output.

error:
       … while calling the 'derivationStrict' builtin
         at <nix/derivation-internal.nix>:37:12:
           36|
           37|   strict = derivationStrict drvAttrs;
             |            ^
           38|

       … while evaluating derivation 'home-manager-generation'
         whose name attribute is located at /nix/store/6bwyhcqsr8pj2gyvdzsr742v9jf2zn52-source/pkgs/stdenv/generic/make-derivation.nix:480:13

       … while evaluating attribute 'buildCommand' of derivation 'home-manager-generation'
         at /nix/store/6bwyhcqsr8pj2gyvdzsr742v9jf2zn52-source/pkgs/build-support/trivial-builders/default.nix:80:17:
           79|         enableParallelBuilding = true;
           80|         inherit buildCommand name;
             |                 ^
           81|         passAsFile = [ "buildCommand" ] ++ (derivationArgs.passAsFile or [ ]);

       … while evaluating the option `home.activation.checkFilesChanged.data':

       … while evaluating definitions from `/nix/store/a4la088hi5id7sw77gy9zdvwn83dgczz-source/modules/files.nix':

       … while evaluating the option `home.file."Library/Fonts/.home-manager-fonts-version".onChange':

       … while evaluating definitions from `/nix/store/a4la088hi5id7sw77gy9zdvwn83dgczz-source/modules/targets/darwin/fonts.nix':

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: The option `home.sessionVariables.ZELLIJ_AUTO_EXIT' has conflicting definition values:
       - In `/nix/store/v2ihm623javngxbmzy5gmgmjq4r2j56w-source/modules/programs/zellij.nix': "true"
       - In `/nix/store/a4la088hi5id7sw77gy9zdvwn83dgczz-source/modules/programs/zellij.nix': "false"
       Use `lib.mkForce value` or `lib.mkDefault value` to change the priority on any of these definitions.
Nix crashed. This is a bug. Please report this at https://github.com/NixOS/nix/issues with the following information included:

Exception: std::__1::system_error: mutex lock failed: Invalid argument
Stack trace:
 0# nix::(anonymous namespace)::onTerminate() in /nix/store/g4fn2b8j3cfs3vci0fam4iws8nikd4wn-nix-2.28.5/bin/nix
 1# std::__terminate(void (*)()) in /nix/store/sg5gfy9cj0991jbd4xfyrl21rmqib9r2-libcxx-19.1.7/lib/libc++abi.1.0.dylib
 2# __cxa_get_exception_ptr in /nix/store/sg5gfy9cj0991jbd4xfyrl21rmqib9r2-libcxx-19.1.7/lib/libc++abi.1.0.dylib
 3# __cxxabiv1::failed_throw(__cxxabiv1::__cxa_exception*) in /nix/store/sg5gfy9cj0991jbd4xfyrl21rmqib9r2-libcxx-19.1.7/lib/libc++abi.1.0.dylib
 4# std::__1::__throw_system_error[abi:ne190107](std::__1::error_code, char const*) in /nix/store/sg5gfy9cj0991jbd4xfyrl21rmqib9r2-libcxx-19.1.7/lib/libc++.1.0.dylib
 5# std::__1::__throw_system_error[abi:ne190107](std::__1::error_code, char const*) in /nix/store/sg5gfy9cj0991jbd4xfyrl21rmqib9r2-libcxx-19.1.7/lib/libc++.1.0.dylib
 6# std::__1::mutex::try_lock() in /nix/store/sg5gfy9cj0991jbd4xfyrl21rmqib9r2-libcxx-19.1.7/lib/libc++.1.0.dylib
 7# nix::updateWindowSize() in /nix/store/g4fn2b8j3cfs3vci0fam4iws8nikd4wn-nix-2.28.5/lib/libnixutil.dylib
 8# nix::signalHandlerThread(unsigned int) in /nix/store/g4fn2b8j3cfs3vci0fam4iws8nikd4wn-nix-2.28.5/lib/libnixutil.dylib
 9# void* std::__1::__thread_proxy[abi:fe190107]<std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct>>, void (*)(unsigned int), unsigned int>>(void*) in /nix/store/g4fn2b8j3cfs3vci0fam4iws8nikd4wn-nix-2.28.5/lib/libnixutil.dylib
10# _pthread_start in /usr/lib/system/libsystem_pthread.dylib

/Users/<username>/.nix-profile/bin/home-manager: line 544:  2267 Abort trap: 6           nix build "${extraArgs[@]}" "${PASSTHROUGH_OPTS[@]}"

[xokdvium]

What version of macOS are you running? I suppose that this bug stems from the fact that all versions of nixpkgs ship a custom version of libc++ that leads to cursed ODR violations and that blows up since macOS 26. This issue should be resolved with nixpkgs 25.11 or current unstable, but there's still some time until release.

[jakubkaczor]

I do run macOS 26, but the issue occurred also with the previous version (15, Sequoia).

[edolstra]

This looks like a duplicate of #14300. Can you check if this issue still occurs on current Nix (2.32 or master)?