Windows Toasts From Emacs Within WSL

20 January, 2022

With some PowerShell and Emacs Lisp, you can easily pop up a native Windows toast straight from Emacs, even within WSL.

I wanted my Org Mode scheduled reminders and deadlines to interrupt my attention while I’m working on my laptop. There is the wonderful org-alert package, which uses the equally fantastic alert Emacs package, but unfortunately libnotify toasts wouldn’t work for me on Windows Subsystem for Linux (WSL).

Thankfully, WSL has built-in command line capability to reach back into the host Windows system, which lets me run this PowerShell¹ script:

param($Title)
$ErrorActionPreference = "Stop"
[Windows.UI.Notifications.ToastNotificationManager, Windows.UI.Notifications, ContentType = WindowsRuntime] > $null
$Template = [Windows.UI.Notifications.ToastNotificationManager]::GetTemplateContent([Windows.UI.Notifications.ToastTemplateType]::ToastText02)

$RawXml = [xml] $Template.GetXml()
($RawXml.toast.visual.binding.text | Where-Object { $_.id -eq "1" }).AppendChild($RawXml.CreateTextNode($Title)) > $null
($RawXml.toast.visual.binding.text | Where-Object { $_.id -eq "2" }).AppendChild($RawXml.CreateTextNode($args[0])) > $null

$SerializedXml = New-Object Windows.Data.Xml.Dom.XmlDocument
$SerializedXml.LoadXml($RawXml.OuterXml)

$Toast = [Windows.UI.Notifications.ToastNotification]::new($SerializedXml)
$Toast.ExpirationTime = [DateTimeOffset]::Now.AddMinutes(30)

$Notifier = [Windows.UI.Notifications.ToastNotificationManager]::CreateToastNotifier("Emacs")
$Notifier.Show($Toast);

…via an Emacs Lisp function (in Emacs running within WSL):

(defun toast (title message)
  (with-temp-buffer
    (shell-command
     (concat
      ;; replace the path to the powershell script to wherever you saved it
      "powershell.exe -ExecutionPolicy Bypass -File ~/path/to/toast.ps1 -Title"
      " \""
      title
      "\" \""
      message
      "\" > /dev/null 2>&1")
     t)))

…which lets me script a toast by calling it like this:

(toast "This Is a Title" "This is some longer text content below the title")

For a basic toast, that’s all you need! You can stop here if all you were interested in was toasting from within WSL.² Read on for some additional tips in setting up org-alert and alert.

Integration with org-alert and alert

By following alert’s documentation, I learned to create my own simplified alert style which called into my toast function.

(alert-define-style 'wsl :title "WSL Toast"
                    :notifier
                    (lambda (info)
                      (toast (plist-get info :title) (plist-get info :message))))

;; set the default alert style to the one we just created
(setq alert-default-style 'wsl)

You can test that it’s working properly by executing this, which should pop up a toast as if you were calling the toast function manually:

(alert "Text content" :title "Title")

Now org-alert just needs to be configured to your liking, and you’ll get basic toasts in Windows for all your agenda events.

Footnotes:

The old, system-provided PowerShell (a.k.a. powershell.exe) is needed here, as the Notification modules don’t seem to be loadable in PowerShell Core (a.k.a. pwsh.exe)

Since we’re just calling powershell.exe with shell-command, this would probably work outside WSL, directly in Windows too.