Precompiled Emacs Lisp packages are not reusable among all Emacs flavors

[AndersonTorres]

Describe the bug

When using an Emacs flavor different from the default one, the Elisp packages are locally compiled; no Elisp package is retrieved from Hydra caches.

This is a bit ridiculous, given that Emacs goes into the slow Staging branch because it causes too much mass rebuilds in order to compile Emacs Lisp packages - and only one of the various flavors provided by Nix is compatible with these compiled packages.

Steps To Reproduce

$ nix store ls --store https://cache.nixos.org/ $(nix eval --raw github:nixos/nixpkgs/nixos-unstable#legacyPackages.x86_64-linux.emacs.pkgs.magit.outPath)
./nix-support
./share

$ nix store ls --store https://cache.nixos.org/ $(nix eval --raw github:nixos/nixpkgs/nixos-unstable#legacyPackages.x86_64-linux.emacs-nox.pkgs.magit.outPath)
error: path '/nix/store/qzqw54kxiccp3ji8awk9qfpwza5yxa8p-emacs-magit-20240522.204' is not a valid store path

Expected behavior

Elisp packages being grabbed from Hydra cache instead of being compiled locally.

Additional context

https://discourse.nixos.org/t/why-is-emacs-lisp-framework-updates-taking-so-long-to-reach-unstable/47416

Notify maintainers

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[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/why-is-emacs-lisp-framework-updates-taking-so-long-to-reach-unstable/47416/17