chore: Let shell.nix depend on nix flake

It's usually better to have one source of truth (regarding package
sources/versions) than two. So, use the compatibility mixin for those
who want to keep using shell.nix.

GHC 9.2 is not supported anymore ("end of life".) Thus, we don't need
overrides for it.

flake.nix

@@ -4,6 +4,7 @@
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
     flake-utils.url = "github:numtide/flake-utils";
+    flake-compat.url = "https://flakehub.com/f/edolstra/flake-compat/1.tar.gz";
   };
 
   outputs = inputs@{ self, nixpkgs, flake-utils, ... }:

shell.nix

@@ -1,17 +1,10 @@
-let
-  # cure = x: pkgs.haskell.lib.dontCheck (pkgs.haskell.lib.doJailbreak x);
-  haskellOverlay = self: super: {
-    haskellPackages = super.haskell.packages.ghc922.override {
-      overrides = hself: hsuper: rec {
-        ghc-lib-parser = hsuper.ghc-lib-parser_9_2_2_20220307;
-      };
-    };
-  };
-in
-{ pkgs ? import <nixpkgs> { overlays = [ haskellOverlay ]; } }:
-
-pkgs.mkShell {
-  buildInputs = [
-    pkgs.haskellPackages.ormolu_0_5_0_0
-  ];
-}
+(import
+  (
+    let lock = builtins.fromJSON (builtins.readFile ./flake.lock); in
+    fetchTarball {
+      url = lock.nodes.flake-compat.locked.url or "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
+      sha256 = lock.nodes.flake-compat.locked.narHash;
+    }
+  )
+  { src = ./.; }
+).shellNix