Add Nix flake for direnv (#6635)

* Add Nix flake for direnv

* Use Sai's suggestion for the `description`

* Make `.envrc` optional

* Move Nix docs to their own section

* Tweak wording

* Tweak wording more

* Add `nixfmt`

---------

Co-authored-by: Sai Praveen Bangaru <31557731+saipraveenb25@users.noreply.github.com>
Co-authored-by: Ellie Hermaszewska <ellieh@nvidia.com>

4 files changed, 110 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
index c6fa15457..79c3559b4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -12,6 +12,8 @@
 *.zip
 *.ini
 *.DS_store
+.direnv
+.envrc
 .gdb_history
 .vimspector
 .vimspector.json
diff --git a/docs/building.md b/docs/building.md
index 504e4e10c..6597c5199 100644
--- a/docs/building.md
+++ b/docs/building.md
@@ -311,6 +311,20 @@ cmake --preset vs2022 --fresh -A arm64 -DSLANG_GENERATORS_PATH=generators/bin
 cmake --build --preset release
 ```
 
+### Nix
+
+This repository contains a [Nix](https://nixos.org/)
+[flake](https://wiki.nixos.org/wiki/Flakes) (not officially supported or
+tested), which provides the necessary prerequisites for local development. Also,
+if you use [direnv](https://direnv.net/), you can run the following commands to
+have the Nix environment automatically activate when you enter your clone of
+this repository:
+
+```bash
+echo 'use flake' >> .envrc
+direnv allow
+```
+
 ## Building with an older CMake
 
 Because older CMake versions don't support all the features we want to use in
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 000000000..c3c585c60
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,61 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1742206328,
+        "narHash": "sha256-q+AQ///oMnyyFzzF4H9ShSRENt3Zsx37jTiRkLkXXE0=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "096478927c360bc18ea80c8274f013709cf7bdcd",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 000000000..211e5f107
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,33 @@
+{
+  description = "The Slang Shading Language and Compiler";
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+  outputs =
+    {
+      self,
+      nixpkgs,
+      flake-utils,
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+      in
+      {
+        devShell =
+          with pkgs;
+          mkShell {
+            buildInputs = [
+              cmake
+              llvm
+              ninja
+              nixfmt-rfc-style
+              python3
+              xorg.libX11
+            ];
+          };
+      }
+    );
+}