Enforce synchronisation of pin-depends with flake.lock (#24)

.nix/sync-pin-depends.nix

@@ -0,0 +1,29 @@
+{ ... }: {
+  perSystem = { pkgs, ... }:
+    let
+      sync-pin-depends = pkgs.writeShellApplication {
+        name = "sync-pin-depends";
+        text = ''
+          printf "Finding revision or Morbig in \`flake.lock\`... "
+          rev=$(jq -r .nodes.morbig.locked.rev flake.lock)
+          printf 'done! got %s.\n' "$rev"
+          printf "Writing it in \`morsmall.opam.template\`... "
+          sed -i "s|morbig#\(.*\)\"|morbig#$rev\"|" morsmall.opam.template
+          printf 'done.\n'
+        '';
+        runtimeInputs = with pkgs; [ jq ];
+      };
+    in {
+      apps.sync-pin-depends = {
+        type = "app";
+        program = sync-pin-depends;
+      };
+
+      pre-commit.settings.hooks.sync-pin-depends = {
+        enable = true;
+        entry = "${sync-pin-depends}/bin/sync-pin-depends";
+        files = "(flake\\.lock$)|(\\.opam\\.template$)";
+        pass_filenames = false;
+      };
+    };
+}

flake.nix

@@ -21,6 +21,7 @@
       imports = [
         ./.nix/with-nixpkgs.nix
         ./.nix/with-opam-nix.nix
+        ./.nix/sync-pin-depends.nix
         inputs.pre-commit-hooks.flakeModule
       ];