Add nix flake and direnv config (#2694)

.envrc

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

.gitignore

@@ -17,6 +17,7 @@
 .env.development.local
 .env.test.local
 .env.production.local
+.direnv
 
 npm-debug.log*
 yarn-debug.log*

flake.lock

@@ -0,0 +1,62 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1718470082,
+        "narHash": "sha256-u2F0MMYE+Efc+ocruTbtU/wWHuYHWcJafp5zJ++n/YE=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "3027ba73dfef68eb555fc2fa97aed4e999e74f97",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs_2": {
+      "locked": {
+        "lastModified": 1718428119,
+        "narHash": "sha256-WdWDpNaq6u1IPtxtYHHWpl5BmabtpmLnMAx0RdJ/vo8=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "e6cea36f83499eb4e9cd184c8a8e823296b50ad5",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs",
+        "rust-overlay": "rust-overlay"
+      }
+    },
+    "rust-overlay": {
+      "inputs": {
+        "nixpkgs": "nixpkgs_2"
+      },
+      "locked": {
+        "lastModified": 1718681902,
+        "narHash": "sha256-E/T7Ge6ayEQe7FVKMJqDBoHyLhRhjc6u9CmU8MyYfy0=",
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "rev": "16c8ad83297c278eebe740dea5491c1708960dd1",
+        "type": "github"
+      },
+      "original": {
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,70 @@
+{
+  description = "modeling-app development environment";
+
+  # Flake inputs
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    rust-overlay.url = "github:oxalica/rust-overlay"; # A helper for Rust + Nix
+  };
+
+  # Flake outputs
+  outputs = { self, nixpkgs, rust-overlay }:
+    let
+      # Overlays enable you to customize the Nixpkgs attribute set
+      overlays = [
+        # Makes a `rust-bin` attribute available in Nixpkgs
+        (import rust-overlay)
+        # Provides a `rustToolchain` attribute for Nixpkgs that we can use to
+        # create a Rust environment
+        (self: super: {
+          rustToolchain = super. rust-bin.stable.latest.default.override {
+            targets = [ "wasm32-unknown-unknown" ];
+            extensions = [ "rustfmt" "llvm-tools-preview" ];
+          };
+        })
+      ];
+
+      # Systems supported
+      allSystems = [
+        "x86_64-linux" # 64-bit Intel/AMD Linux
+        "aarch64-linux" # 64-bit ARM Linux
+        "x86_64-darwin" # 64-bit Intel macOS
+        "aarch64-darwin" # 64-bit ARM macOS
+      ];
+
+      # Helper to provide system-specific attributes
+      forAllSystems = f: nixpkgs.lib.genAttrs allSystems (system: f {
+        pkgs = import nixpkgs { inherit overlays system; };
+      });
+
+    in
+    {
+      # Development environment output
+      devShells = forAllSystems ({ pkgs }: {
+        default = pkgs.mkShell {
+          # The Nix packages provided in the environment
+          packages = (with pkgs; [
+            # The package provided by our custom overlay. Includes cargo, Clippy, cargo-fmt,
+            # rustdoc, rustfmt, and other tools.
+            rustToolchain
+
+            cargo-llvm-cov
+            cargo-nextest
+
+            just
+            postgresql.lib
+            openssl
+            pkg-config
+
+            nodejs_22
+          ]) ++ pkgs.lib.optionals pkgs.stdenv.isDarwin (with pkgs; [
+            libiconv 
+            darwin.apple_sdk.frameworks.Security
+          ]);
+
+          TARGET_CC = "${pkgs.stdenv.cc}/bin/${pkgs.stdenv.cc.targetPrefix}cc";
+          LIBCLANG_PATH = "${pkgs.libclang.lib}/lib";
+        };
+      });
+    };
+}