In exwm (Emacs X Window Manager) how can I assign apps to particular workspaces?

Question

For example, no matter in which workspace I start Firefox, I want it to launch in workspace 2. In i3wm I can do this with assign [class="(?i)firefox"] $workspace2.

Answer 1

You can use exwm-manage-finish-hook to perform functions when a window has loaded. Combine that with exwm-class-name and exwm-workspace-move-window and you could do something like this:

(require 'subr-x)  ;; Because of when-let

(defvar exwm-workspace-window-assignments
  '(("Firefox" . 2)
    ("Thunderbird" . 3))
  "An alist of window classes and which workspace to put them on.")

(add-hook 'exwm-manage-finish-hook
          (lambda ()
            (when-let ((target (cdr (assoc exwm-class-name exwm-workspace-window-assignments))))
              (exwm-workspace-move-window target))))

So now a window named Firefox would end up on workspace 2, while Thunderbird would end up on workspace 3. You could add more entries to exwm-workspace-window-assignments if you want. Keep in mind that the workspace need to exist before trying to move a window to it.

The code snippet above needs Emacs 25, because of when-let.

Answer 2

There is a way to set this using EXWM settings (it is possible that this option did not exist at the time the question was first answered):

(setq exwm-manage-configurations
   '((string= exwm-instance-name "firefox")
      workspace 2))

You can also set this variable with M-x customize-variable Ret exwm-manage-configurations.