feat(cpp): add nix build stuff

.gitignore

@@ -1,3 +1,6 @@
 build/
 *.o
 *~
+cpp/flake.nix
+cpp/flake.lock
+cpp/.direnv/*

cpp/.envrc

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

cpp/Makefile

@@ -0,0 +1,23 @@
+BUILD_DIR := build
+
+.PHONY: all configure build clean run
+
+all: build
+
+configure:
+	cmake -S . -B $(BUILD_DIR) -G Ninja \
+	  -DCMAKE_BUILD_TYPE=Debug \
+	  -DCMAKE_C_COMPILER=clang \
+	  -DCMAKE_CXX_COMPILER=clang++
+		-DBUILD_CLI_VIS=1
+
+build: configure
+	cmake --build $(BUILD_DIR)
+	@# Symlink compile_commands.json to root so clangd picks it up
+	@ln -sf $(BUILD_DIR)/compile_commands.json compile_commands.json
+
+run: build
+	./$(BUILD_DIR)/myapp
+
+clean:
+	rm -rf $(BUILD_DIR) compile_commands.json

cpp/flake.nix

@@ -0,0 +1,28 @@
+{
+  description = "C++ dev shell with CMake and clangd";
+
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  outputs = { self, nixpkgs }:
+    let
+      systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
+      forAll = f: nixpkgs.lib.genAttrs systems (s: f nixpkgs.legacyPackages.${s});
+    in {
+      devShells = forAll (pkgs: {
+        default = pkgs.mkShell {
+          packages = with pkgs; [
+            cmake
+            clang-tools   # provides clangd, clang-format, clang-tidy
+            llvmPackages.clang
+            ninja         # optional but pairs well with cmake
+            catch2        # testing framework
+          ];
+
+          shellHook = ''
+            export CC=clang
+            export CXX=clang++
+          '';
+        };
+      });
+    };
+}