Add Nix flake for ergonomic NixOS development (#253)

Author: alxmrs

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -14,3 +14,4 @@ test_data
 CHANGELOG.md
 *.ipynb
 /site
+.direnv

.python-version

@@ -1 +1 @@
-3.11
+3.12

CONTRIBUTING.md

@@ -16,6 +16,25 @@ We use [uv](https://docs.astral.sh/uv/) to manage the project. This project
 also contains a Rust extension (built with [maturin](https://www.maturin.rs/)),
 so a Rust toolchain is required.
 
+<details>
+<summary>NixOS user?</summary>
+
+This repo ships a `flake.nix` that provides uv, a matching Python
+interpreter, and a Rust toolchain, plus the shared libraries that compiled
+Python wheels (pyarrow, duckdb, polars, ...) expect to find at runtime —
+none of which NixOS provides by default. It's scoped to this project only;
+it doesn't touch anything outside this directory.
+
+- With [direnv](https://direnv.net/) installed, run `direnv allow` once in
+  the project root and the shell loads automatically whenever you `cd` in
+  (and unloads when you leave).
+- Without direnv, run `nix develop` manually to enter the shell.
+
+Either way, once you're in the shell, skip steps 0-1 below (Rust and uv are
+already on `PATH`) and start at step 2.
+
+</details>
+
 0. Install Rust: https://rustup.rs/
 1. Install uv: https://docs.astral.sh/uv/getting-started/installation/
 2. Clone the repository (bonus: [via SSH](https://docs.github.com/en/authentication/connecting-to-github-with-ssh/adding-a-new-ssh-key-to-your-github-account))

flake.lock

@@ -0,0 +1,44 @@
+{
+  description = "xarray-sql development environment";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+
+        # Shared libraries that manylinux wheels (pyarrow, duckdb, polars,
+        # numpy, ...) expect to find via the dynamic linker at runtime.
+        # NixOS doesn't put these on a standard FHS path, so we point
+        # LD_LIBRARY_PATH at the nix store paths that provide them.
+        runtimeLibs = with pkgs; [
+          stdenv.cc.cc
+          zlib
+          openssl
+        ];
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          packages = with pkgs; [
+            uv
+            python312
+            rustc
+            cargo
+            pkg-config
+          ];
+
+          # Use the Nix-provided interpreter above instead of having uv
+          # download its own Python build.
+          UV_PYTHON_PREFERENCE = "only-system";
+
+          shellHook = ''
+            export LD_LIBRARY_PATH="${pkgs.lib.makeLibraryPath runtimeLibs}''${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}"
+            echo "xarray-sql dev shell: $(python3 --version), $(rustc --version)"
+          '';
+        };
+      });
+}