@adisbladis @alyssais @tadfisher I noticed that ofborg didn't add a reviewer for this, so I am tagging people that worked on this recently to get the ball rolling. Feel free to ignore this if you don't have time or just don't want to do it :)

If you want to test this locally, please use an updated gccemacs version since I was hitting a bug was fixed upstream today. The current version on emacs-overlay is fine.

The "emacsHookDone=1" part is admittedly very hacky, suggestions are appreciated.

You could split addToEmacsLoadPath, addToEmacsNativeLoadPath, and addEmacsVars into a separate file (e.g. emacs-funcs.sh) and source it from both setupHook and postInstall.

{
  setupHook = ''
    source ${./emacs-funcs.sh}

    if [[ ! -v emacsHookDone ]]; then
      emacsHookDone=1

      # If this is for a wrapper derivation, emacs and the dependencies are all
      # run-time dependencies. If this is for precompiling packages into bytecode,
      # emacs is a compile-time dependency of the package.
      addEnvHooks "$hostOffset" addEmacsVars
      addEnvHooks "$targetOffset" addEmacsVars
    fi
  '';

  postInstall = ''
    # Make sure the current package's elisp files are in load-path, otherwise
    # (require 'file-b) from file-a.el in the same package will fail.
    source ${./emacs-funcs.sh}
    addEmacsVars "$out"

    # ...
  '';
}

So basically rename setup-hook.sh so maintainers don't get confused and move the hook install into setupHook in the derivation.

Can you also try removing the --eval=\"(add-to-list 'comp-eln-load-path \\\"$out/share/emacs/native-lisp/\\\")\" stanza from the native compile command and compare the output?

Thanks for the great refactoring idea! Since setupHook expects a file name and not the file's contents, I had to sprinkle writeText in a few places. Let me know if this is a bad idea :) Even then, I believe the refactored approach is much cleaner.

I get a bunch of (error "Cannot find suitable directory for output in `comp...") errors when removing the --eval stanza. I believe this happens because addToEmacsNativeLoadPath tests if $nativeDir is a directory before it gets created by the native compilation process. I went ahead and created the directory manually, but I can revert that if you prefer.

As a data point, here's the number of compiled files in my configuration before and after this patch:

$ ls /nix/store/cjjg220sg767052s39z4967f16divazw-emacs-packages-deps/share/emacs/native-lisp/28.0.50-x86_64-pc-linux-gnu-98ea6c3cd3377ce4e7a0782a2e12f0e9/*.eln | wc -l
526

$ ls /nix/store/2r28p285qad5s43n0pp85rmjfz0xxv40-emacs-packages-deps/share/emacs/native-lisp/28.0.50-x86_64-pc-linux-gnu-98ea6c3cd3377ce4e7a0782a2e12f0e9/*.eln | wc -l
1158

@adisbladis Can you take a look at this?

There were some merge conflicts, but I've now rebased my commit. @adisbladis, sorry for pinging you again :)