Perspective for Emacs

Description

The Perspective package provides multiple named workspaces (or "perspectives") in Emacs, similar to multiple desktops in window managers like Awesome and XMonad, and Spaces on the Mac.

Each perspective has its own buffer list and its own window layout. This makes it easy to work on many separate projects without getting lost in all the buffers. Switching to a perspective activates its window configuration, and when in a perspective, only its buffers are available (by default).

Each Emacs frame has a distinct list of perspectives.

Perspective supports saving its state to a file, so long-lived work sessions may be saved and recovered as needed.

Sample Use Cases

Multiple Projects

Working on multiple projects can become difficult to organize as their buffer lists mix together during a long-running Emacs session. Searching for a buffer by name works well if you know what to search for, but sometimes picking from a list is easier — in which case, keeping the list well-pruned for relevant buffers becomes an important source of efficiency in file and buffer management. Perspective helps out by letting you keep separate named buffer lists and window layouts.

This use case works really well in conjunction with Projectile. Projectile helps with buffer navigation (and other project-specific tasks) in cases when a project has a well-defined root directory. Perspective then steps in to help manage unrelated buffers: shells, REPLs, dired buffers visiting directories outside the project, or files relevant to the project not under the same root as the rest of the source. It also helps deal with the situation of one project with multiple source repositories where having a shared window layout or buffer list makes sense.

Yak Shaving

Suppose you're developing feature X in perspective feature-X. This keeps you working with one set of files and windows. You then realize that this feature requires you to fix a bug in an unrelated set of files. You don't want to lose all the context you have built up for feature X, so you open a new perspective, bugfix-Y, letting you open new files and buffers without disturbing your work on feature-X. Then you are asked to urgently look into something related to development of feature Z, but again: you don't want to lose context. So you open a new perspective feature-Z, and fill it with a whole bunch of new files and windows — all without losing any of the context for your work on bug Y or feature X.

When you finish looking at Z, you close perspective feature-Z, and return to bugfix-Y, and restore its window layout and buffer list. When you finish with Y, you close perspective bugfix-Y and return to feature-X.

(Hint: this workflow works best with the persp-sort variable set to 'created — see documentation below.)

Similar Packages

The following Emacs packages implement comparable functionality:

persp-mode: A Perspective fork, which implements perspective sharing between Emacs frames. It also has a different approach to saving state and different configuration options. There has been some interest expressed in merging the two projects. Due to conflicting function names, persp-mode.el and Perspective cannot be installed simultaneously.
Workgroups 2: Similar to Perspective in terms of features. Its original codebase seems to predate Emacs acquiring a native ability to serialize window layouts, so it has custom serialization code.
eyebrowse: Supports window layouts but not buffer lists.
wconf: Supports window layouts but not buffer lists.
ElScreen: Supports window layouts but not buffer lists; seems unmaintained.

Emacs 27 includes two new buffer and window organizing features: Tab Line (global-tab-line-mode) and Tab Bar (tab-bar-mode).

Tab Line maintains a list of buffers which had been opened in a given window, and anchors it to that window. It is analogous to tabs as used in web browsers and other text editors, and therefore orthogonal to Perspective.
Tab Bar maintains window layouts (with optional names). In this, it is similar to Perspective. Unlike Perspective, it does not support buffer lists. Using Perspective and Tab Bar at the same time is not recommended at this time, since the tab list is global (i.e., will show up in all perspectives) and is likely to cause confusion. It would be an interesting future feature for Perspective to adopt the tab bar and allow keeping a distinct set of tabs per-perspective.

Compatibility

Perspective does not work with Emacs desktop.el. This is because Perspective state stores buffer and window information in frame parameters, and desktop-save-mode does not support saving those types of data.

Instead, Perspective provides its own disk save and load feature, which cleanly saves perspectives.

Installation

You should install Perspective from MELPA or MELPA Stable.

Users of use-package can install Perspective as follows:

(use-package perspective
  :config
  (persp-mode))

Alternately, put perspective.el from this source repository in your load path and run (require 'perspective).

Users of Debian 9 or later or Ubuntu 16.04 or later may simply apt-get install elpa-perspective, though be aware that the stable version provided in these repositories is likely to be (extremely) outdated.

Usage

To activate perspective use (persp-mode). This creates a single default main perpsective.

Commands are all prefixed by C-x x by default. To change the prefix key, customize persp-mode-prefix-key. Additionally, creating a key binding for persp-mode-map will also activate the prefix.

Here are the main commands defined in persp-mode-map:

s — persp-switch: Query a perspective to switch to, or create
k — persp-remove-buffer: Query a buffer to remove from current perspective
c — persp-kill : Query a perspective to kill
r — persp-rename: Rename current perspective
a — persp-add-buffer: Query an open buffer to add to current perspective
A — persp-set-buffer: Add buffer to current perspective and remove it from all others
b - persp-switch-to-buffer: Like switch-to-buffer; includes all buffers from all perspectives; changes perspective if necessary
i — persp-import: Import a given perspective from another frame.
n, <right> — persp-next: Switch to next perspective
p, <left> — persp-prev: Switch to previous perspective
C-s — persp-state-save: Save all perspectives in all frames to a file
C-l — persp-state-load: Load all perspectives from a file

Since Perspective maintains distinct buffer lists for each perspective, it helps to use a Perspective-aware buffer switcher.

Ido: Interactive Do (Ido, ido-mode), in particular its ido-switch-buffer command, is automatically Perspective-aware when persp-mode is enabled.

bs.el: Perspective provides a wrapper for bs-show: persp-bs-show. When this function is called normally, it shows a list of buffers filtered by the current perspective. With a prefix argument, it shows a list of buffers in all perspectives.

IBuffer: Perspective provides a wrapper for ibuffer: persp-ibuffer. When this function is called normally, it shows a list of buffers filtered by the current perspective. With a prefix argument, it shows a list of buffers in all perspectives.

Helm: Perspective ships with buffer-listing advice for Helm, so Helm's buffer listing code should be automatically Perspective-aware when persp-mode is enabled. (Older versions of Helm relied on the machinery of ido-mode for listing buffers, so they did not require this advice; see this Helm commit and this Perspective commit for details.)

Ivy / Counsel: Perspective provides two commands for listing buffers using Ivy and Counsel: persp-ivy-switch-buffer and persp-counsel-switch-buffer. When these functions are called normally, they show a list of buffers filtered by the current perspective. With a prefix argument, they shows a list of buffers in all perspectives. The distinction between the ivy and counsel versions is the same as between ivy-switch-buffer and counsel-switch-buffer: the latter shows a preview of the buffer to switch to, and the former does not.

Globally binding one of these helper functions to a buffer-switching key is a good idea, e.g.:

(global-set-key (kbd "C-x C-b") (lambda (arg)
                                  (interactive "P")
                                  (if (fboundp 'persp-bs-show)
                                      (persp-bs-show arg)
                                    (bs-show "all"))))

Notes on `completing-read` Enhancements

Users of a completing-read enhancement framework (such as Ivy or Selectrum) may wish to use the following two functions:

persp-switch-to-buffer* replaces switch-to-buffer
persp-kill-buffer* replaces kill-buffer

Both these functions behave like the built-ins, but use completing-read directly. When called normally, they list buffers filtered by the current perspective. With a prefix argument, they list buffers in all perspectives.

The following sample use-package invocation changes Emacs default key bindings to use the replacements:

(use-package perspective
  :bind (("C-x b" . persp-switch-to-buffer*)
         ("C-x k" . persp-kill-buffer*))
  :config
  (persp-mode))

Saving Sessions to Disk

A pair of functions, persp-state-save and persp-state-load, implement perspective durability on disk. When called interactively, they prompt for files to save sessions to and restore from.

A custom variable, persp-state-default-file, sets a default file to use for saving and restoring perspectives. When it is set, persp-state-save may be called non-interactively without an argument and it will save to the file referenced by that variable. This makes it easy to automatically save perspective sessions when Emacs exists:

(add-hook 'kill-emacs-hook #'persp-state-save)

A limitation of persp-state-save and persp-state-load is that they do not attempt to deal with non-file-visiting buffers with non-trivial state. Saving shell, REPL, and compilation-mode buffers is not supported. When saved to a file, any windows pointing to them are changed to point to the perspective's *scratch* buffer. (Live windows are, of course, left alone.)

Customization

Perspective supports several custom variables (see its section in M-x customize). The following are likely to be of most interest:

persp-sort: Select the order in which to sort perspectives when calling persp-switch. Defaults to 'name (alphabetical), but 'access (by most recently accessed) and 'created (by order created) are available.
persp-interactive-completion-function: Used for prompting for a perspective name. completing-read is the default, with ido-completing-read enabled with ido-mode. ivy-completing-read is broadly compatible, but unfortunately sorts alphabetically and therefore breaks the persp-sort setting. Helm, unfortunately, does not have a completing-read compatible implementation out of the box (helm-completing-read-default-1 purports to be this but does not have the same &optional defaults). ido-completing-read is the recommended setting here unless a completing-read enhancement framework is used.
persp-mode-prefix-key: Changes the default key prefix for Perspective commands.
persp-state-default-file: Changes the default file to use for saving and loading Perspective state.

Some Musings on Emacs Window Layouts

The following discussion exceeds the needs of documenting Perspective, but it falls in the category of helping users learn to manage Emacs sessions, and therefore will likely help potential users of Perspective make the experience smoother.

Emacs has bad default behavior when it comes to window handling: many commands and modes have a habit of splitting existing windows and changing the user's carefully thought-out window layout. This tends to be a more serious problem for people who run Emacs on large displays (possibly in full-screen mode): the greater amount of screen real estate makes it easy to split the frame into many smaller windows, making any unexpected alterations more disruptive.

As a result of indiscriminate-seeming window splits and buffer switching in existing windows, new Emacs users can get into the habit of expecting Emacs and its packages to lack basic respect for their layouts. Hence the popularity of things like winner-mode, and packages like shackle.

This may make the value of Perspective seem questionable: why bother with carefully preserving window layouts if Emacs just throws them away on a M-x compile? The answer is to fix the broken defaults. This is fairly easy:

(setq display-buffer-alist
      '((".*" (display-buffer-reuse-window display-buffer-same-window))))

(setq display-buffer-reuse-frames t)         ; reuse windows in other frames
(setq even-window-sizes nil)                 ; display-buffer: avoid resizing

The Emacs framework responsible for "pop-up" windows is display-buffer. The relevant section of the Emacs manual is dense and difficult to read, so there have been attempts to summarize the most important bits:

The suggested settings above do the following:

Tell display-buffer to reuse existing windows as much as possible, including in other frames. For example, if there is already a *compilation* buffer in a visible window, switch to that window. This means that Emacs will usually switch windows in a "do what I mean" manner for a warmed-up workflow (one with, say, a couple of source windows, a compilation output window, and a Magit window).
Prevent splits by telling display-buffer to switch to the target buffer in the current window. For example, if there is no *compilation* buffer visible, then the buffer in whichever window was current when compile was run will be replaced with *compilation*. This may seem intrusive, since it changes out the current buffer, but keep in mind that most buffers popped up in this manner are easy to dismiss, either with a dedicated keybinding (often q) or the universally-applicable M-x kill-buffer. This is easier than restoring window arrangements. It is also easier to handle for pre-arranged window layouts, since the appropriate command can simply be run in a window prepared for it in advance. (If this is a step too far, then replace display-buffer-same-window with display-buffer-pop-up-window.)

gcentauri/perspective-el