build: Add nix flake

Nix is such an improved developer environment experience. I am planning
to also replace the current CI and update the documentation soon.

(temporarily disable static builds until the CI rework)

.github/workflows/ci.yaml

@@ -35,9 +35,9 @@ jobs:
         run: |
           export RUSTFLAGS='-L /usr/lib/x86_64-linux-gnu'
           cargo build
-      - name: Static build
-        run: |
-          just build
+      # - name: Static build
+      #   run: |
+      #     just build
   lint:
     name: Lint
     runs-on: ubuntu-22.04

build.rs

@@ -74,7 +74,7 @@ fn main() {
     let skel = Path::new(RUBY_STACK_SKELETON);
     match SkeletonBuilder::new()
         .source(RUBY_STACK_SOURCE)
-        .clang_args("-Wextra -Wall -Werror")
+        .clang_args("-Wextra -Wall -Werror -Wno-unused-command-line-argument")
         .build_and_generate(skel)
     {
         Ok(_) => {}
@@ -101,7 +101,7 @@ fn main() {
     let skel = Path::new(FEATURES_SKELETON);
     match SkeletonBuilder::new()
         .source(FEATURES_SOURCE)
-        .clang_args("-Wextra -Wall -Werror")
+        .clang_args("-Wextra -Wall -Werror -Wno-unused-command-line-argument")
         .build_and_generate(skel)
     {
         Ok(_) => {}

flake.nix

@@ -0,0 +1,63 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+    rust-overlay = {
+      url = "github:oxalica/rust-overlay";
+      inputs = {
+        nixpkgs.follows = "nixpkgs";
+        flake-utils.follows = "flake-utils";
+      };
+    };
+  };
+  outputs = { self, nixpkgs, flake-utils, rust-overlay }:
+    flake-utils.lib.eachSystem [ "x86_64-linux" "aarch64-linux" ]
+      (system:
+        let
+          overlays = [ (import rust-overlay) ];
+          pkgs = import nixpkgs {
+            inherit system overlays;
+          };
+          elfutils-without-zstd = pkgs.elfutils.overrideAttrs (attrs: {
+            configureFlags = attrs.configureFlags ++ [ "--without-zstd" ];
+          });
+        in
+        with pkgs;
+        {
+          formatter = pkgs.nixpkgs-fmt;
+
+          devShells.default = mkShell rec {
+            # https://discourse.nixos.org/t/how-to-add-pkg-config-file-to-a-nix-package/8264/4
+            nativeBuildInputs = with pkgs; [
+              pkg-config
+            ];
+            buildInputs = [
+              rust-bin.stable.latest.default
+              llvmPackages_16.clang
+              # llvmPackages_16.clang-unwrapped https://github.com/NixOS/nixpkgs/issues/30670
+              llvmPackages_16.libcxx
+              llvmPackages_16.libclang
+              llvmPackages_16.lld
+              # Debugging
+              strace
+              gdb
+              # Native deps
+              glibc
+              glibc.static
+              elfutils-without-zstd
+              zlib.static
+              zlib.dev
+              openssl
+              # Other tools
+              cargo-edit
+              # snapshot testing plugin binary
+              cargo-insta
+              # ocamlPackages.magic-trace
+            ];
+
+            LIBCLANG_PATH = lib.makeLibraryPath [ llvmPackages_16.libclang ];
+            LD_LIBRARY_PATH = lib.makeLibraryPath [ zlib.static elfutils-without-zstd ];
+          };
+        }
+      );
+}