Add flakes and improve CDeclarationItem

Author: kalhauge

flake.lock

@@ -0,0 +1,58 @@
+{
+  inputs = {
+    nixpkgs.url = github:nixos/nixpkgs/nixpkgs-unstable;
+    flake-utils.url = github:numtide/flake-utils;
+  };
+  outputs = {
+    self,
+    nixpkgs,
+    flake-utils,
+    ...
+  } @ inputs: let
+    packages = final: p: {
+      "language-c" =
+        final.haskell.lib.overrideCabal
+        (p.callCabal2nixWithOptions "language-c" "${self}" "" {}) {
+          doCheck = false;
+        };
+    };
+    overlays = final: prev: {
+      haskellPackages = prev.haskellPackages.extend (p: _: packages final p);
+    };
+  in
+    {
+      overlays.default = overlays;
+    }
+    // flake-utils.lib.eachDefaultSystem
+    (system: let
+      hpkgs =
+        (import nixpkgs {
+          inherit system;
+          overlays = [overlays];
+        })
+        .haskellPackages;
+    in rec {
+      packages = {
+        default = hpkgs.language-c;
+        language-c = hpkgs.language-c;
+      };
+      devShells = let
+        buildInputs = with hpkgs; [
+          cabal-install
+          ghcid
+          haskell-language-server
+          hpack
+          fourmolu
+        ];
+        withHoogle = true;
+      in {
+        default =
+          hpkgs.shellFor
+          {
+            name = "language-c-shell";
+            packages = p: [p.language-c];
+            inherit buildInputs withHoogle;
+          };
+      };
+    });
+}