spacemacs/EXPERIMENTAL.org

#+TITLE: Spacemacs experimental features

* Table of contents                                       :TOC_4_gh:noexport:
- [[#spacemacs-dumps-using-the-portable-dumper][Spacemacs dumps using the portable dumper]]
  - [[#setup][Setup]]
    - [[#clone-emacs][Clone Emacs]]
    - [[#simple-patch-of-emacs-source-code][Simple patch of Emacs source code]]
    - [[#compile-emacs-from-source][Compile Emacs from source]]
      - [[#macos][MacOS]]
    - [[#update-your-dotfile][Update your dotfile]]
    - [[#test][Test]]
    - [[#report-issues][Report issues]]
  - [[#usage][Usage]]

* Spacemacs dumps using the portable dumper
The portable dumper is a feature that may be availabe with Emacs 27.1, for now
its code is in the =pdumper= branch of the Emacs Git repository, it has not been
merged to master yet.

This should theoretically work on all the three major OSes: GNU/Linux, MacOS and
Windows.

** Setup
To test the portable dumper with Spacemacs, follow these steps:

*** Clone Emacs
Clone Emacs from [[https://git.savannah.gnu.org/git/emacs.git]]:

#+BEGIN_SRC shell
  git clone https://git.savannah.gnu.org/git/emacs.git
  cd emacs
  git checkout pdumper
#+END_SRC

*** Simple patch of Emacs source code
We need to increase the number of =remember_data= slots in =src/pdumper.c=, we
double the number of slots by replacing 32 with 64:

#+BEGIN_SRC c
static struct
{
  void *mem;
  int sz;
} remembered_data[64];
#+END_SRC

*** Compile Emacs from source
This step depends on your OS (please create a PR to add the instructions for
your OS).

**** MacOS
In the root directory of your freshly cloned Emacs repository and with the
=pdumper= branch as the current branch:

#+BEGIN_SRC shell
  ./autogen.sh
  ./configure --with-ns --with-dbus --with-gnutls --with-imagemagick --with-rsvg  --with-mailutils --with-xml2 --with-modules
#+END_SRC

*** Update your dotfile
A new user dotfile function has been added which is called before doing the
dump. The function name is =dotspacemacs/user-load=.

You can copy/paste the following snippet in your dotfile and provide a
value for =dotspacemacs-emacs-pdumper-executable-file= which must point to
the Emacs executable you compiled at the previous step. For me it was:
"~/dev/emacs/src/emacs"

#+BEGIN_SRC emacs-lisp
(defun dotspacemacs/user-load ()
  "Library to load while dumping.
This function is called while dumping Spacemacs configuration. You can
`require' or `load' the libraries of your choice that will be included
in the dump."
  (setq-default

   ;; Absolute file path pointing to emacs 27.1 executable compiled with support
   ;; for the portable dumper (this is currently the branch pdumper)
   ;; If nil then automatic Emacs dump is disabled.
   ;; (default nil)
   dotspacemacs-emacs-pdumper-executable-file nil

   ;; Name of the Spacemacs dump file. This is the file will be created by the
   ;; portable dumper in the cache directory under dumps sub-directory.
   ;; To load it when starting Emacs add the parameter `--dump-file'
   ;; when invoking Emacs 27.1 executable on the command line, for instance:
   ;;   ./emacs --dump-file=/Users/sylvain/.emacs.d/.cache/dumps/spacemacs.pdmp
   ;; (default spacemacs.pdmp)
   dotspacemacs-emacs-dumper-dump-file "spacemacs.pdmp"))
#+END_SRC

*** Test
Checkout the =moon= branch in `.emacs.d` and launch your Emacs as you usually
do. It can be Emacs 25.1 or later this is not important but obviously you can
also use the compiled Emacs version.

Each time Emacs starts, Spacemacs will check if the list of your layers has
changed, if it has changed then Emacs will be automatically dumped for you in
an asynchronous process. The buffer for the output of the process is named
=*spacemacs dumper*=.

If you have no error during the dump you can test it out!

To actually start Spacemacs with the compiled Emacs 27.1 and the Spacemacs dump,
on the command line in the =src= directory of the cloned Emacs source:

#+BEGIN_SRC shell
  ./emacs --dump-file=/Users/sylvain/.emacs.d/.cache/dumps/spacemacs.pdmp &
#+END_SRC

*** Report issues
If you want to report an issue regarding this new feature please use the label
=Portable Dumper=.

All the related issues can be found with [[https://github.com/syl20bnr/spacemacs/labels/Portable%20Dumper][this link]].

** Usage
Once =dotspacemacs-emacs-pdumper-executable-file= is set to a non-nil and valid
file path to an Emacs 27.1 executable Emacs will be redumped automatically each
time the layer list changes or the =--force-dump= parameter is passed on the
command line.

To use the created dump file, open a shell in the =src= directory of the cloned
Emacs source and type:

#+BEGIN_SRC shell
  ./emacs --dump-file=/Users/sylvain/.emacs.d/.cache/dumps/spacemacs.pdmp &
#+END_SRC

=spacemacs.pdmp= corresponds the value of the variable
=dotspacemacs-emacs-dumper-dump-file=.