Add initial Nix shell (#8530)

* Add initial Nix shell

* Update flake.nix

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

.envrc

@@ -0,0 +1 @@
+use nix

.gitignore

@@ -50,3 +50,6 @@ idf_component.yml
 CMakeLists.txt
 /sdkconfig.*
 .dummy/*
+
+# PYTHONPATH used by the Nix shell
+.python3

flake.lock

@@ -0,0 +1,44 @@
+{
+  "nodes": {
+    "flake-compat": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1767039857,
+        "narHash": "sha256-vNpUSpF5Nuw8xvDLj2KCwwksIbjua2LZCqhV1LNRDns=",
+        "owner": "NixOS",
+        "repo": "flake-compat",
+        "rev": "5edf11c44bc78a0d334f6334cdaf7d60d732daab",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "repo": "flake-compat",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1766314097,
+        "narHash": "sha256-laJftWbghBehazn/zxVJ8NdENVgjccsWAdAqKXhErrM=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "306ea70f9eb0fb4e040f8540e2deab32ed7e2055",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-compat": "flake-compat",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,66 @@
+{
+  description = "Nix flake to compile Meshtastic firmware";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+
+    # Shim to make flake.nix work with stable Nix.
+    flake-compat = {
+      url = "github:NixOS/flake-compat";
+      flake = false;
+    };
+  };
+
+  outputs =
+    inputs:
+    let
+      lib = inputs.nixpkgs.lib;
+
+      forAllSystems =
+        fn:
+        lib.genAttrs lib.systems.flakeExposed (
+          system:
+          fn {
+            pkgs = import inputs.nixpkgs {
+              inherit system;
+            };
+            inherit system;
+          }
+        );
+    in
+    {
+      devShells = forAllSystems (
+        { pkgs, ... }:
+        let
+          python3 = pkgs.python312.withPackages (
+            ps: with ps; [
+              google
+            ]
+          );
+        in
+        {
+          default = pkgs.mkShell {
+            buildInputs = with pkgs; [
+              python3
+              platformio
+            ];
+
+            shellHook = ''
+              # Set up PlatformIO to use a local core directory.
+              export PLATFORMIO_CORE_DIR=$PWD/.platformio
+              # Tell pip to put packages into $PIP_PREFIX instead of the usual
+              # location. This is especially necessary under NixOS to avoid having
+              # pip trying to write to the read-only Nix store. For more info,
+              # see https://wiki.nixos.org/wiki/Python
+              export PIP_PREFIX=$PWD/.python3
+              export PYTHONPATH="$PIP_PREFIX/${python3.sitePackages}"
+              export PATH="$PIP_PREFIX/bin:$PATH"
+              # Avoids reproducibility issues with some Python packages
+              # See https://nixos.org/manual/nixpkgs/stable/#python-setup.py-bdist_wheel-cannot-create-.whl
+              unset SOURCE_DATE_EPOCH
+            '';
+          };
+        }
+      );
+    };
+}

shell.nix

@@ -0,0 +1,12 @@
+(import (
+  let
+    lock = builtins.fromJSON (builtins.readFile ./flake.lock);
+    nodeName = lock.nodes.root.inputs.flake-compat;
+  in
+  fetchTarball {
+    url =
+      lock.nodes.${nodeName}.locked.url
+        or "https://github.com/NixOS/flake-compat/archive/${lock.nodes.${nodeName}.locked.rev}.tar.gz";
+    sha256 = lock.nodes.${nodeName}.locked.narHash;
+  }
+) { src = ./.; }).shellNix