#+TITLE: Spacemacs-purpose layer

#+TAGS: layer|spacemacs|util

* Table of Contents                     :TOC_5_gh:noexport:
- [[#description][Description]]
  - [[#features][Features:]]
- [[#purposes][Purposes]]
  - [[#switch-to-buffer-and-display-buffer][switch-to-buffer and display-buffer]]
  - [[#misc][misc]]
- [[#install][Install]]
- [[#usage][Usage]]
- [[#key-bindings][Key bindings]]
- [[#caveats][Caveats]]
  - [[#popwin-and-guide-key][Popwin and guide-key]]
  - [[#packages-that-do-display-management][Packages that do display management]]

* Description
This layer enables [[https://github.com/bmag/emacs-purpose][window-purpose]], which provides an alternative, purpose-based
window manager for Emacs. With this layer, your window layout should be robust
and shouldn't change too much when opening all sorts of buffers.

Regular [[https://github.com/m2ym/popwin-el][popwin]] is not triggered when window-purpose is enabled. However,
the window-purpose layer provides a =purpose-popwin= extension, which
brings popwin's behavior to window-purpose and solves that problem.

** Features:
- Window layout is more robust and less likely to change unintentionally
- Dedicate window to a purpose
- User-defined purposes
- Extensible window display behavior
- Empty =purpose-mode-map=, to avoid conflicts with other key maps
- Replicate popwin behavior for purpose-mode - almost no regression in popup behavior from using window-purpose.
- Reuses popwin's settings: =popwin:special-display-config=, =popwin:popup-window-height= and =popwin:popup-window-width=.
- Difference from popwin: when several windows are open, popup window is sometimes bigger than with regular popwin in the same situation.

* Purposes
window-purpose contains a configuration which assigns a purpose for each
buffer. Later, when Emacs needs to display a buffer in a window, its purpose
helps make a better decision of which window to use.

For example, consider the following case: Emacs frame shows three windows - one
for code, one for a terminal and one general-purpose window. The general window
is selected and you want to open a code file. How do you ensure that the code
file will be displayed in the code window? With window-purpose you don't
need to worry about it - you open the file and window-purpose places it in
the correct window.

Additionally, you can dedicate a window to a purpose - so that window is
reserved only for buffers that share that purpose.

** switch-to-buffer and display-buffer
In regular Emacs, =switch-to-buffer= follows different rules than the other
switching and popping commands, because it doesn't use =display-buffer= (which
the other commands do). With window-purpose, this behavior is fixed. The
result is a better control over how buffers are displayed, since
=switch-to-buffer= doesn't ignore the user's customizations anymore.

** misc
- specialized helm source similar to =helm-source-buffers-list=

* Install
To use this configuration layer, add it to your =~/.spacemacs=. You will need to
add =spacemacs-purpose= to the existing =dotspacemacs-configuration-layers= list in
this file.

* Usage
With window-purpose layer installed, =purpose-mode= and =pupo-mode= are enabled.
You can toggle =purpose-mode= (~SPC : purpose-mode~) at any time to return to
purpose-less behavior. You can toggle =pupo-mode= (~SPC : pupo-mode~) to turn
off only the purpose-popwin integration.

If you change =popwin:special-display-config= in your =dotspacemacs/config=, you
should call =pupo/update-purpose-config= to update purpose-popwin with those
changes.

See [[https://github.com/bmag/emacs-purpose/wiki][window-purpose wiki]] to learn more about window-purpose.

* Key bindings

| Key binding | Description                                                                         |
|-------------+-------------------------------------------------------------------------------------|
| ~SPC r b~   | Open a buffer. Only buffers with the same purpose as the current buffer are listed. |
| ~SPC r B~   | Open any buffer and ignore window-purpose when displaying the buffer.               |
| ~SPC r d~   | Toggle dedication of selected window to its current purpose.                        |
| ~SPC r D~   | Delete all non-dedicated windows.                                                   |
| ~SPC r p~   | Choose a purpose and open a buffer with that purpose.                               |
| ~SPC r P~   | Change the purpose of the selected window. Changes the window's buffer accordingly. |

* Caveats
** Popwin and guide-key
If a buffer is displayed in two different windows, and only one of those windows
is purpose-dedicated, then invoking guide-key will cause both windows to become
purpose-dedicated.

** Packages that do display management
Some packages that manage how windows are displayed, such as =gdb= with
=gdb-many-windows=, might not play nicely with =window-purpose=. However, it is
usually possible to find a solution. After all, even =helm= and =popwin= work
with =window-purpose=.