Given that Emacs 29 is considered beta, it will not be aliased to `emacs`.
And, given that Emacs 29 ships with Pure GTK feature, why not to make it
available?
A list of modifications:
- The calling handles at `top-level/all-packages.nix` were transferred to
`pkgs/applications/editors/emacs/default.nix` (the good old `recurseIntoAttrs`
design pattern);
- The files `macport.nix` and `28.nix` were removed, replaced by the bigger and
better `sources.nix`;
- Aliases for the most important derivations were put on `all-packages.nix`;
- The file `generic.nix` was refactored. Among its changes, the most noticeable:
- `pname` is decorated according to the selected UI options;
- Environment variables are explicitly under `env` set;
- The `null` defaults and (in)equality tests were removed;
- It obliged the addition of some Boolean flag guards;
- The flag `noGui` was added, allowing easier override for `emacs-nox`.
With this huge refactor, the emacs build functions become more sane and
maintainable, allowing future additions.
