programmatically place generated files in development environment

this allows to add more generated files later as needed without
cluttering the `shellHook`.

panel/default.nix

@@ -12,10 +12,11 @@ let
   manage = pkgs.writeScriptBin "manage" ''
     exec ${pkgs.lib.getExe pkgs.python3} ${toString ./src/manage.py} $@
   '';
+  package = pkgs.callPackage ./nix/package.nix { };
 in
 {
   shell = pkgs.mkShellNoCC {
-    inputsFrom = [ (pkgs.callPackage ./nix/package.nix { }) ];
+    inputsFrom = [ package ];
     packages = [
       pkgs.npins
       manage
@@ -26,7 +27,10 @@ in
       DATABASE_URL = "sqlite:///${toString ./src}/db.sqlite3";
     };
     shellHook = ''
-      ln -sf ${sources.htmx}/dist/htmx.js src/panel/static/htmx.min.js
+      ${lib.concatStringsSep "\n" (
+        map (file: "ln -sf ${file.from} ${toString ./src/${file.to}}") package.generated
+      )}
+
       # in production, secrets are passed via CREDENTIALS_DIRECTORY by systemd.
       # use this directory for testing with local secrets
       mkdir -p $CREDENTIALS_DIRECTORY

panel/nix/package.nix

@@ -25,6 +25,12 @@ let
     packages = [ "${name}" ]
     include-package-data = true
   '';
+  generated = [
+    {
+      from = "${sources.htmx}/dist/htmx.min.js";
+      to = "./panel/static/htmx.min.js";
+    }
+  ];
 in
 python3.pkgs.buildPythonPackage {
   pname = name;
@@ -54,11 +60,17 @@ python3.pkgs.buildPythonPackage {
     ]
     ++ pythonPackages;
 
+  passthru = {
+    inherit generated;
+  };
+
   postInstall = ''
     mkdir -p $out/bin
     cp -v ${src}/manage.py $out/bin/manage.py
     chmod +x $out/bin/manage.py
     wrapProgram $out/bin/manage.py --prefix PYTHONPATH : "$PYTHONPATH"
-    cp ${sources.htmx}/dist/htmx.min.js* $out/${python3.sitePackages}/panel/static/
+    ${lib.concatStringsSep "\n" (
+      map (file: "cp ${file.from} $out/${python3.sitePackages}/${file.to}") generated
+    )}
   '';
 }