How to show C/C++ doxygen section titles in the mode-line?

Question

For C/C++ code that use doxygen sections, it would be useful to show these in the mode-line, without slowing down the mode-line display significantly.

Is there a good way to add context information to the mode-line?

Answer 1

The built-in which-function package already does something similar, getting the function.

You can extend this using advice, this way which-function handles the timers and accesses the current function, you can add extra information to this as needed.

(with-eval-after-load 'which-func
  (defun which-function--add-comment-section (orig-fn)
    (let ((result (funcall orig-fn)))
      (when result
        (setq result (propertize result 'face 'font-lock-keyword-face)))

      ;; Error's are very unlikely, this is to ensure even the most remote
      ;; chance of an error, don't cause which-func to fail.
      (condition-case err
        (let ((section nil))
          (cond
            ((member major-mode '(c-mode c++-mode glsl-mode))
              (save-match-data
                (save-excursion
                  (when (re-search-backward "\\([\\\@]\}\\|[\\\@]\{\\)" nil t 1)
                    (pcase (char-after (+ 1 (point)))
                      (?{ ;; Section Start
                        (let ((section-start-pt (point)))
                          ;; Find start of comment.
                          (when (re-search-backward "\\/\\*" nil t 1)
                            (when
                              (re-search-forward
                                "[\\@]name[[:blank:]]+\\(.*\\)"
                                section-start-pt
                                t
                                1)
                              (setq section
                                (propertize
                                  (match-string-no-properties 1)
                                  'face
                                  'font-lock-comment-face))))))
                      (?} ;; Section End
                        ;; Do nothing, we're not in a section.
                        nil)))))))

          (when section
            (setq result (concat section ": " (or result which-func-unknown)))))
        (error (message "Error creating vc-backend root name: %s" err)))
      result))
  (advice-add 'which-function :around #'which-function--add-comment-section))

This matches sections written in this style.

/** \name Main Function
 * 
 * Body text.
 * \{ */

/* --- your code --- */

/** \} */

When the cursor is in "your code" the mode line will show the function name and section text.

The mode line needs to include something like this:

'(:eval (when (bound-and-true-p which-func-mode) (list " (" which-func-current ")")))