Documentation request: Emacs packages installed via emacsWithPackagesFromUsePackage but configured via default.el or emacs.el using use-package

[573]

{...}:{
overlays = [
 (final: prev: {
  somemore = prev.lib.composeManyExtensions [ inputs.emacs-overlay.overlays.default ] final prev;
  my-emacs = final.somemore.emacsWithPackagesFromUsePackage {
   config = "${rootPath}/home/misc/emacs.el";
   alwaysEnsure = true;
   defaultInitFile = final.substituteAll {
     name = "default.el";
     src = "${final.runCommand "emacs-config" {
      inherit rootPath;
      input = builtins.readFile "${rootPath}/home/misc/emacs.el";
     } ''
       mkdir -p "$out/"
       printf '%s\n' "
        ;; use-package.outPath is not writable
        (defun my-bytecomp-dest-file (source)
        (expand-file-name (file-name-nondirectory source) \"~/.cache/\"))
        (setq byte-compile-dest-file-function 'my-bytecomp-dest-file)
        (access-file \"${final.somemore.emacsUnstable-nox.pkgs.melpaPackages.use-package.outPath}\" \"use-package path not readable\")
        (add-to-list 'load-path \"~/.cache/\")
        (add-to-list 'load-path \"${final.somemore.emacsUnstable-nox.pkgs.melpaPackages.use-package.outPath}\")
        (eval-when-compile
         (package-initialize)
         (require 'use-package))" > $out/emacs.el
       printf '%s\n' "$input" >> $out/emacs.el
     ''}/emacs.el";
    };
   extraEmacsPackages = epkgs: (with epkgs.melpaPackages; [
      use-package
      company-emoji
   ]);
  };
 })
];
}

;; file $rootpath/home/misc/emacs.el
(use-package company-emoji
  :config (add-to-list 'company-backends 'company-emoji))

EDIT: I have use-package as well in the set and added a byte-compile helper to my elisp to circumvent nix trying to write *.elc files to the store path.
Building my flake with these edits now says default.el:18:12: Error: Cannot open load file: No such file or directory, use-package:

nix-repl> :u nixosConfigurations.DANIELKNB1.pkgs.my-emacs
warning: error: plugin-files set after plugins were loaded, you may need to move the flag before the subcommand
these 5 derivations will be built:
/nix/store/144vkiwdpr20v819m14gnsfwsjma9v63-emacs-config.drv
/nix/store/8ynkd1ny34df2gzbn12h1ynjz3y6ynas-default.el.drv
/nix/store/j3a9byj0ig8inrv8akhhgcjf8z82f31f-emacs-default-init-file.drv
/nix/store/i9nysbxpcis792vrwsmalkzsznhq7jl5-emacs-packages-deps.drv
/nix/store/09j84gimq61q57n3zbkp6maq3cyl3sss-emacs-unstable-with-packages-28.2-nox.drv
building '/nix/store/144vkiwdpr20v819m14gnsfwsjma9v63-emacs-config.drv'...
building '/nix/store/8ynkd1ny34df2gzbn12h1ynjz3y6ynas-default.el.drv'...
building '/nix/store/j3a9byj0ig8inrv8akhhgcjf8z82f31f-emacs-default-init-file.drv'...
unpacking sources
unpacking source archive /nix/store/rs4dfkvdcw1v8c94ys544mcf21pmwvdm-default.el
source root is .
patching sources
configuring
no configure script, doing nothing
building

In toplevel form:
default.el:18:12: Error: Cannot open load file: No such file or directory, use-package
error: builder for '/nix/store/j3a9byj0ig8inrv8akhhgcjf8z82f31f-emacs-default-init-file.drv' failed with exit code 1;
last 10 log lines:
> unpacking sources
> unpacking source archive /nix/store/rs4dfkvdcw1v8c94ys544mcf21pmwvdm-default.el
> source root is .
> patching sources
> configuring
> no configure script, doing nothing
> building
>
> In toplevel form:
> default.el:18:12: Error: Cannot open load file: No such file or directory, use-package
For full logs, run 'nix log /nix/store/j3a9byj0ig8inrv8akhhgcjf8z82f31f-emacs-default-init-file.drv'.
error: 1 dependencies of derivation '/nix/store/09j84gimq61q57n3zbkp6maq3cyl3sss-emacs-unstable-with-packages-28.2-nox.drv' failed to build
error: program 'nix-shell' failed with exit code 1

Also when starting built emacs it says:

>Warning (initialization): An error occurred while loading ‘/.emacs’:~
>
>Symbol's value as variable is void: company-emoji
>
>To ensure normal operation, you should investigate and remove the
cause of the error in your initialization file. Start Emacs with
the ‘--debug-init’ option to view a complete error backtrace. Disable showing Disable logging

I thought setting alwaysEnsure true (#43) would take care of this.