What’s the theme?

Last time 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-locking 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 StackExchange, 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))))))