dots/chemacs/.emacs.d/README.org

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* Chemacs

Chemacs 2 is an Emacs profile switcher, it makes it easy to run multiple Emacs
configurations side by side.

Think of it as a bootloader for Emacs.

** Differences from Chemacs 1

Emacs intialization used to have a single entry point, either =~/.emacs= or
=~/.emacs.d/init.el=. More recent Emacsen have introduced a second startup
script, =~/.emacs/early-init.el=, which runs earlier in the boot process, and
can be used for things that should happen very early on, like tweaking the GC,
or disabling UI elements.

Chemacs 2 supports =early-init.el=, Chemacs 1 does not. This does also imply
that Chemacs 2 needs to be installed as =~/.emacs.d= (a directory), rather than
simply linking it to =~/.emacs= (a single file).

** Rationale

Emacs configuration is either kept in a =~/.emacs= file or, more commonly, in a
=~/.emacs.d= directory. These paths are hard-coded. If you want to try out
someone else's configuration, or run different distributions like Prelude or
Spacemacs, then you either need to swap out =~/.emacs.d=, or run Emacs with a
different =$HOME= directory set.

This last approach is quite common, but has some real drawbacks, since now
packages will no longer know where your actual home directory is.

All of these makes trying out different Emacs configurations and distributions
needlessly cumbersome.

Various approaches to solving this have been floated over the years. There's an
Emacs patch around that adds an extra command line option, and various examples
of how to add a command line option in userspace from Emacs Lisp.

Chemacs tries to implement this idea in a user-friendly way, taking care of the
various edge cases and use cases that come up.

** Installation

Clone the Chemacs 2 repository as =$HOME/.emacs.d=. Note that if you already
have an Emacs setup in =~/.emacs.d= you need to move it out of the way first. If
you have an =~/.emacs= startup script then move that out of the way as well.

#+BEGIN_SRC shell
  [ -f ~/.emacs ] && mv ~/.emacs ~/.emacs.bak
  [ -d ~/.emacs.d ] && mv ~/.emacs.d ~/.emacs.default
  git clone https://github.com/plexus/chemacs2.git ~/.emacs.d
#+END_SRC

Note that this is different from Chemacs 1. Before Chemacs installed itself as
=~/.emacs= and you could have your own default setup in =~/.emacs.d=. This
approach no longer works because of =~/.emacs.d/early-init.el=, so Chemacs 2
needs to be installed as =~/.emacs.d=.

Next you will need to create a =~/.emacs-profiles.el= file, for details see
below.

#+begin_src emacs-lisp
  (("default" . ((user-emacs-directory . "~/.emacs.default"))))
#+end_src

** Usage

Chemacs adds an extra command line option to Emacs, =--with-profile=. Profiles
are configured in =~/.emacs-profiles.el=.

If no profile is given at the command line then the =default= profile is used.

#+BEGIN_SRC shell
$ emacs --with-profile my-profile
#+END_SRC

There is an option for using profile that is not preconfigured in =~/.emacs-profiles.el=. To accomplish that you can directly provide the profile via the command line, like so
#+BEGIN_SRC shell
$ emacs --with-profile '((user-emacs-directory . "/path/to/config"))'
#+END_SRC
This method supports all the profile options given below.

** .emacs-profiles.el

This file contains an association list, with the keys/cars being the profile
names, and the values/cdrs their configuration.

The main thing to configure is the =user-emacs-directory=

#+BEGIN_SRC emacs-lisp
  (("default" . ((user-emacs-directory . "~/.emacs.default")))
   ("spacemacs" . ((user-emacs-directory . "~/spacemacs"))))
#+END_SRC

Chemacs will set this to be the =user-emacs-directory= in use, and load
=init.el= from that directory.

Other things you can configure

- =custom-file= : The file where Customize stores its customizations. If this
  isn't configured, and the =custom-file= variable is still unset after loading
  the profile's =init.el=, then this will get set to the profile's =init.el=
- =server-name= : Sets the =server-name= variable, so you can distinguish multiple
  instances with =emacsclient -s <server-name>=.
- =env= An association list of environment variables. These will get set before
  loading the profile, so they can influence the initialization, and they are
  visible to any subprocesses spawned from Emacs.
- =straight-p= Enable the [[https://github.com/raxod502/straight.el][Straight]]
  functional package manager.

Store =.emacs-profiles.el= together with your dotfiles. If you're not yet keeping
a version controlled directory of dotfiles, then check out
[[https://github.com/plexus/dotfiles/blob/master/connect-the-dots][connect-the-dots]]
for a helpful script to do that.

** Changing the default profile (e.g. for GUI editors)

Where it is not possible to use the =--with-profile= flag, the default profile
can be set using a =~/.emacs-profile= file.

If your =~/.emacs-profiles.el= file contains the following:

#+BEGIN_SRC emacs-lisp
  (("default" . ((user-emacs-directory . "~/.emacs.default")))
   ("spacemacs" . ((user-emacs-directory . "~/spacemacs")))
   ("prelude" . ((user-emacs-directory . "~/prelude"))))
#+END_SRC

you can create a file called =~/.emacs-profile=, containing the name of the
profile you'd like to be used when none is given on the command line:

#+BEGIN_SRC shell
$ echo 'spacemacs' > ~/.emacs-profile
#+END_SRC

This will set the default profile to be the "spacemacs" profile, instead of
"default". You can change the default by simply changing the contents of this
file:

#+BEGIN_SRC shell
$ echo 'prelude' > ~/.emacs-profile
#+END_SRC

If this file doesn't exist, then "default" will be used, as before.

** Spacemacs

Spacemacs is typically installed by cloning the Spacemacs repo to =~/.emacs.d=,
and doing extra customization from =~/.spacemacs= or =~/.spacemacs.d/init.el=.
This makes it tedious to switch between version of Spacemacs, or between
different Spacemacs configurations.

With Chemacs you can point your =user-emacs-directory= to wherever you have
Spacemacs installed, and use the =SPACEMACSDIR= environment variable to point at
a directory with customizations that are applied on top of the base install.

#+BEGIN_SRC emacs-lisp
(("spacemacs" . ((user-emacs-directory . "~/spacemacs")
                 (env . (("SPACEMACSDIR" . "~/.spacemacs.d")))))

 ("spacemacs-develop" . ((user-emacs-directory . "~/spacemacs/develop")
                        (env . (("SPACEMACSDIR" . "~/.spacemacs.d")))))

 ("new-config" . ((user-emacs-directory . "~/spacemacs/develop")
                  (env . (("SPACEMACSDIR" . "~/my-spacemacs-config"))))))
#+END_SRC

** DOOM emacs

You can add an entry similar to the following to your =.emacs-profiles.el=

In the following snippet =~/doom-emacs= is where you have cloned doom emacs.

(Depending on when you read this) =DOOMDIR= support is only in =develop= branch of doom emacs. Check commit history of =master= branch of doom emacs

#+BEGIN_SRC emacs-lisp
("doom" . ((user-emacs-directory . "~/doom-emacs")
           (env . (("DOOMDIR" . "~/doom-config")))))
#+END_SRC

Please refer to [[https://github.com/plexus/chemacs/issues/5][this]] discussion for details.

** FreeDesktop Directories

Both =~/.emacs-profiles.el= and =~/.emacs-profile= can also be stored under =$XDG_CONFIG_HOME/chemacs= (typically =~/.config/chemacs=) as =$XGD_CONFIG_HOME/chemacs/profiles.el= and =$XDG_CONFIG_HOME/chemacs/profile= respectively.

Further, as indicated by the [[http://git.savannah.gnu.org/cgit/emacs.git/tree/etc/NEWS?h=emacs-27][Emacs 27.1 changelog]], Emacs is now compatible with XDG Standards, looking for its configuration files in =${XDG_CONFIG_HOME}/emacs= directory too (provided the traditional =~/.emacs.d= and =~/.emacs= does not exist).
Therefore, it is perfectly viable to install Chemacs 2 in =${XDG_CONFIG_HOME}/emacs= (usually =~/.config/emacs=) directory - with the aforementioned caveat: _the directory =~/.emacs.d"= and the file ="~/.emacs"= does not exist_.

** LICENSE

Copyright © Arne Brasseur 2018-2020

Distributed under the terms of the GPL v3.