magneto: Composable Window Management for Emacs

Window management in Emacs is either too simple or too opinionated. split-window-right and split-window-below are basic primitives that require manual sequencing. purpose and shackle give you declarative rules but take away direct control. What I wanted was something in between: a small grammar of composable operations where I set the parameters I care about and let the system handle the plumbing. magneto is that grammar. Press a key to enter compose mode, set any combination of source action, destination, cursor placement, and buffer action, then press RET to execute.

Here's a common sequence: you're looking at a file and you want to open a related file in a vertical split to the right, keeping your cursor on the original. In vanilla Emacs:

(split-window-right)       ; split
(other-window 1)           ; move to new window
(find-file "related.el")   ; open file
(other-window -1)          ; move back

Every combination of source, destination, cursor, and buffer action is a separate function you'd need to write or find.

Four commands, and you need to remember the sequence. Want to copy the current buffer instead of opening a new file? Different sequence. Want to split below instead of right? Different sequence. Want the cursor to stay in the new window? Omit the last step. Every combination of source, destination, cursor, and buffer action is a separate function you'd need to write or find.

magneto collapses this combinatorial explosion into a single composable flow. Instead of four sequential commands, you press your magneto key, then press modifiers to set whatever differs from the defaults, then execute. The number of keystrokes scales with how much you're customizing, not with the inherent complexity of the operation.

magneto operations have four independent dimensions:

Each dimension has its own keys. You press any combination of them in any order before executing with RET. Any dimension you don't set uses its default. This means the simplest magneto operation (just RET with all defaults) is equivalent to switch-to-buffer in the current window. But adding one or two keys before RET gives you dramatically different behavior.

The source action controls what happens to the origin window after the buffer lands in its destination.

Move is the default and matches the most common intent: relocate a buffer. Copy is useful when you want a reference view alongside an editing view of the same context. Pull is a refinement of move, the buffer leaves, but instead of the window disappearing, it shows whatever was there before.

The destination controls where the buffer ends up.

This is the difference between "open this file over there and keep working here" and "open this file over there and go to it." A small distinction that eliminates a other-window call in half your workflows.

The buffer action controls what appears in the destination window.

Set magneto-buffer-command to #'consult-buffer if you use consult:

(setq magneto-buffer-command #'consult-buffer)

Composing a few simple operations: split right with a file, copy to a split below, move to an existing window.

Pinning buffers to edges using side window destinations.

Pre-selecting a destination window before composing the rest of the operation.

magneto uses ace-window's visual overlay to let you pick a window. The keys a, s, d in the compose keymap pre-select the first, second, or third window by ace-window ordering. This lets you set the destination before you've even decided what to put in it.

magneto includes an optional embark integration module (magneto-embark.el) that routes embark actions through magneto's compose system. The idea: when you act on an embark candidate, you often want to control where the result ends up. Without magneto, embark opens files in the current window. With magneto, you can send them to a split, a side window, or a pre-selected ace-window target.

magneto-embark-bind-keys scans all registered embark keymaps and generates magneto-routed versions of relevant actions (find-file, consult-bookmark, goto-grep, etc.). These are bound under s-o in each embark keymap. So where you'd normally press f in embark to open a file, pressing s-o f opens it through magneto's compose flow instead.

Routing embark actions through magneto to control destination windows.

All defaults are customizable:

magneto is on GitHub. It requires Emacs 29.1+ and depends on avy and ace-window.

(use-package magneto
  :ensure (:host github :repo "chiply/magneto")
  :bind ("s-m" . magneto-compose)
  :custom
  (magneto-buffer-command #'consult-buffer))

For embark integration:

(use-package magneto-embark
  :after (magneto embark)
  :config
  (magneto-embark-bind-keys))

Bind magneto-compose to a comfortable key, press it, and start composing. The which-key popup (if you use which-key) shows all available modifiers. Press RET when you're ready. Start with the defaults and add modifiers as you learn the grammar.