What’s the theme?

Last time¹ I explained how to display your Emacs version with extra useful details. I closed the article saying that there could be more interesting stuff to display, and here I am with something new.

Sometimes I happen to report missing font-locking² or other small issues with faces in a mode I use. Why not have my current colour theme name displayed along with the bits and pieces gathered in the previous article?

As Steve Purcell explained on StackExchange³, the concept of current theme is a bit fuzzy in Emacs. You can have multiple themes on at the same time, just have a look at M-x customize-themes. Moreover, activating a theme means applying its settings to the faces and variables it specifies.

Thus I came up with this little function:

(defun mu--colour-theme ()
  "Get the currently applied colour theme."
  (replace-regexp-in-string
   "[\t\n\r ]+" ""
   (let* ((command (concat "rg load-theme " user-emacs-directory))
          (res (shell-command-to-string command)))
     (nth 1 (split-string res "'")))))

Basically I run ripgrep in my .emacs.d to get the lines containing load-theme. Obviously this will return the line in mu–-colour-theme as well. However, since I use split-string with ' as separator I can get the element I need from the result of ripgrep. nth 1 gives me what I am looking for: sanityinc-tomorrow-night.

Now I can have the active colour theme displayed in my environment details buffer:

;;;###autoload
(defun mu-env-info ()
  "Display Emacs version and system details in a temporary buffer."
  (interactive)
  (let ((buffer-name "*env-info*"))
    (with-help-window buffer-name
      (with-current-buffer buffer-name
        (insert (emacs-version) "\n\n")
        (insert "Repository revision: " emacs-repository-version "\n")
        (when (and system-configuration-options
                   (not (equal system-configuration-options "")))
          (insert "Configured using:\n"
                  system-configuration-options))
        (insert "\n\nEmacs uptime: " (emacs-uptime) "\n")
        (insert "Colour theme: " (mu--colour-theme) "\n")
        (insert "Operating system: " (mu--os-version) "\n")
        (insert "Window system: " (getenv "XDG_SESSION_TYPE") "\n")
        (insert "Desktop environment: " (mu--gnome-version))))))