Fix NixOS CI: use nix python for cmake, venv only for pybind11 pin

FindPython needs the real nix Python (with dev headers), not the venv
wrapper. Save NIX_PYTHON3 before venv overrides PATH. Tested locally.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 65 insertions, 61 deletions

diff --git a/nix/mobase-shell.nix b/nix/mobase-shell.nix
index c39dd02..ae5ad91 100644
--- a/nix/mobase-shell.nix
+++ b/nix/mobase-shell.nix
@@ -1,61 +1,65 @@
-{ pkgs ? import <nixpkgs> {} }:

-

-let

-  python = pkgs.python313;

-  pythonWithPkgs = python.withPackages (ps: [

-    ps.sip

-    ps.pyqt6

-  ]);

-in

-pkgs.mkShell {

-  nativeBuildInputs = with pkgs; [

-    cmake

-    ninja

-    pkg-config

-    git

-    rustc

-    cargo

-  ];

-

-  buildInputs = with pkgs; [

-    # Qt 6

-    qt6.qtbase

-    qt6.wrapQtAppsHook

-    qt6.qtwebengine

-    qt6.qtwebsockets

-    qt6.qtsvg

-    qt6.qtwayland

-

-    # Python

-    pythonWithPkgs

-

-    # Libraries

-    boost

-    sqlite

-    tinyxml-2

-    fontconfig

-    spdlog

-    fuse3

-    libcap

-    lz4

-    zlib

-    zstd

-    bzip2

-    xz

-    openssl

-    curl

-    tomlplusplus

-    fmt

-  ];

-

-  shellHook = ''

-    # Create a temporary venv to install pinned pybind11 (nixpkgs version is too new)

-    if [ ! -d .nix-venv ]; then

-      python3 -m venv .nix-venv --system-site-packages

-      .nix-venv/bin/pip install --quiet pybind11==2.13.6

-    fi

-    export PATH="$PWD/.nix-venv/bin:$PATH"

-    export PYTHONPATH="$PWD/.nix-venv/lib/python3.13/site-packages:$PYTHONPATH"

-    export CMAKE_PREFIX_PATH="${pkgs.qt6.qtbase}:${pkgs.qt6.qtwebengine}:${pkgs.qt6.qtwebsockets}:${pkgs.qt6.qtsvg}:$CMAKE_PREFIX_PATH"

-  '';

-}

+{ pkgs ? import <nixpkgs> {} }:
+
+let
+  python = pkgs.python313;
+  pythonWithPkgs = python.withPackages (ps: [
+    ps.sip
+    ps.pyqt6
+  ]);
+in
+pkgs.mkShell {
+  nativeBuildInputs = with pkgs; [
+    cmake
+    ninja
+    pkg-config
+    git
+    rustc
+    cargo
+  ];
+
+  buildInputs = with pkgs; [
+    # Qt 6
+    qt6.qtbase
+    qt6.wrapQtAppsHook
+    qt6.qtwebengine
+    qt6.qtwebsockets
+    qt6.qtsvg
+    qt6.qtwayland
+
+    # Python (withPackages for runtime, base python313 for dev headers/libpython)
+    pythonWithPkgs
+    python313
+
+    # Libraries
+    boost
+    sqlite
+    tinyxml-2
+    fontconfig
+    spdlog
+    fuse3
+    libcap
+    lz4
+    zlib
+    zstd
+    bzip2
+    xz
+    openssl
+    curl
+    tomlplusplus
+    fmt
+  ];
+
+  shellHook = ''
+    # Save the real nix Python before venv overrides PATH (cmake needs this)
+    export NIX_PYTHON3="$(command -v python3)"
+
+    # Create a temporary venv to install pinned pybind11 (nixpkgs version is too new)
+    if [ ! -d .nix-venv ]; then
+      python3 -m venv .nix-venv --system-site-packages
+      .nix-venv/bin/pip install --quiet pybind11==2.13.6
+    fi
+    export PATH="$PWD/.nix-venv/bin:$PATH"
+    export PYTHONPATH="$PWD/.nix-venv/lib/python3.13/site-packages:$PYTHONPATH"
+    export CMAKE_PREFIX_PATH="${pkgs.qt6.qtbase}:${pkgs.qt6.qtwebengine}:${pkgs.qt6.qtwebsockets}:${pkgs.qt6.qtsvg}:$CMAKE_PREFIX_PATH"
+  '';
+}