add nix flake for easier contribution for nix users

.envrc

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

.gitignore

@@ -82,3 +82,4 @@ bench.html
 
 # Emacs
 .projectile
+/.direnv/

CONTRIBUTING.md

@@ -29,6 +29,16 @@ cabal v2-build Cabal-tests:unit-tests # build Cabal's unit test suite
 cabal v2-build cabal-tests # etc...
 ```
 
+Building Cabal for hacking with Nix (not officially supported)
+--------------------------
+
+```
+nix develop # if you don't have direnv installed
+cabal build cabal
+```
+
+NOTE: Building the cabal library with nix flakes is not officially supported and as such may fall out of date. Be prepared to tweak it and please contribute fixes back.
+
 Running tests
 -------------
 

changelog.d/pr-8753

@@ -0,0 +1,3 @@
+synopsis: add nix flake for easier contribution for nix users
+packages: cabal-install
+prs: #8753

flake.nix

@@ -0,0 +1,19 @@
+{
+  description = "A devshell that enables nix users to just run `cabal build cabal` and start contributing to Cabal";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  };
+
+  outputs = inputs@{ flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = [ "x86_64-linux" "aarch64-darwin" ];
+      perSystem = { config, self', inputs', pkgs, system, ... }: {
+        packages.default = pkgs.lib.trace "This flake currently only contains a devshell for use with nix develop";
+        devShells.default = pkgs.mkShell {
+          buildInputs = [ pkgs.ghc pkgs.cabal-install pkgs.zlib ];
+        };
+      };
+      flake = {};
+    };
+}