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Nix and direnv

This example makes Neovim inherit an existing ESP-IDF environment whenever you enter a project. It does not package or install ESP-IDF with Nix.

That distinction avoids a common failure mode: idf_tools.py install esp-clang cannot write tools into an immutable /nix/store ESP-IDF checkout.

Prerequisites

File placement

Put both files in the ESP-IDF project root, beside its top-level CMakeLists.txt:

your-project/
├── .envrc
├── CMakeLists.txt
├── flake.nix
├── main/
└── sdkconfig

flake.nix

The version name must match the activation script created by EIM:

{
  description = "ESP-IDF activation shell";

  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";

  outputs = { nixpkgs, ... }:
    nixpkgs.lib.genAttrs
      [ "aarch64-darwin" "x86_64-darwin" "aarch64-linux" "x86_64-linux" ]
      (system: {
        devShells.default =
          let
            pkgs = nixpkgs.legacyPackages.${system};
            idfVersion = "v6.0.2";
            eimActivation = "$HOME/.espressif/tools/activate_idf_${idfVersion}.sh";
            manualActivation = "$HOME/esp/esp-idf/export.sh";
          in
          pkgs.mkShell {
            shellHook = ''
              if [ -f "${eimActivation}" ]; then
                source "${eimActivation}"
              elif [ -f "${manualActivation}" ]; then
                source "${manualActivation}"
              else
                echo "ESP-IDF activation script not found." >&2
                echo "Update idfVersion or manualActivation in flake.nix." >&2
                return 1
              fi
            '';
          };
      });
}

The development shell intentionally does not add its own CMake, Python, or toolchains. The ESP-IDF activation script supplies the versions selected for that installation. Add unrelated project tools to packages only when needed.

If you use fish, point the shell hook at a POSIX-compatible activation script or adapt the activation outside mkShell; Nix shell hooks run as shell code and cannot source fish syntax.

.envrc

use flake

Allow it once:

direnv allow

nix-direnv watches .envrc, flake.nix, and flake.lock, so changes reload the environment. Commit flake.lock when the project should use a reproducible Nixpkgs revision.

Verify

From the project directory:

direnv status
idf.py --version
clangd --version
nvim

Inside Neovim, run :ESPInfo.

If idf_tools.py install esp-clang tries to write under /nix/store, the active ESP-IDF still comes from a Nix-packaged checkout. Install esp-clang through that package definition, or use this activation-only approach with a writable EIM/manual installation.