Echo messages in minibuffer

echo-line.el

;;; echo-line.el --- Echo messages in minibuffer  -*- lexical-binding:t -*-
;;
;; Author: Al Haji-Ali <abdo.haji.ali@gmail.com>
;; Version: 0.1.0
;; Package-Requires: ((emacs "26.1"))
;; Keywords: message, echo, gui
;;
;; This file is not part of GNU Emacs.
;;
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;;
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.
;;
;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
;;
;;; Commentary:
;; Based on gist by
;; https://gist.github.com/rougier/096323d35ae3af5c8d0740dbb297f3e5
;;
;; Example usage:
;;
;; (require 'echo-line)
;; ;; Enable `display-time-mode` to update the `display-time-string`
;; (display-time-mode 1)
;; ;; Optionally delete the time string from the mode-line
;; (delete 'display-time-string global-mode-string)
;; ;; Update the echo-line every time the display-time is updated
;; (add-hook 'display-time-hook 'echo-line-update)
;; ;; Set the echo-line format
;; (setq echo-line-format '((:eval display-time-string)))
;; (echo-line-mode)

(require 'subr-x)

;;; Code:

(defface echo-line-face
  '((t :height 0.83
       :overline t))
  "Default face used for the echo line.")

(defcustom echo-line-format nil
  "Template for displaying echo line in the minibuffer.
See `mode-line-format' for more info"
  :type 'sexp)

(defvar echo-line--current nil
  "The current string to display on the next update.")

(defcustom echo-line-text-scale-factor 0.83
  "Scale factor to determine the size of character in the echo-line.
This is in relation to a character form the minibuffer.")

(defun echo-line-update ()
  "Update the echo-line."
  ;; Make sure that we don't run in a TRAMP buffer
  (let ((default-directory "~/"))
    ;; Prevent accidental modification of the current buffer
    (with-temp-buffer
      (setq echo-line--current
            (format-mode-line echo-line-format))
      ;; Apply face while retaining set faces
      (add-face-text-property 0 (length echo-line--current)
                              'echo-line-face t echo-line--current)))
  (echo-line--re-echo))

(defun echo-line--process-message (raw-msg max-width)
  "Process RAW-MSG to be displayed with the echo-line.
MAX-WIDTH is the maximum width for a message."
  (let* ((msg (if-let ((index (text-property-any 0 (length raw-msg)
                                                 'echo-message-start t raw-msg)))
                  (substring raw-msg 0 index)
                raw-msg))
         (lines (if (string-match "\n\\([^\n]*\\)\\'" msg)
                    ;; Extract last line
                    (cons (substring msg 0 (match-beginning 1))
                          (substring msg (match-beginning 1)))
                  (cons "" msg)))
         (last-line (truncate-string-to-width
                     (cdr lines)
                     max-width
                     nil nil "…")))
    (concat (car lines) last-line)))

(defun echo-line--message@advice (orig-fun &rest args)
  "Message advice that add the echoed string to the message.
This advice displays the regular message in the echo area and
adds a specific text on the right part of the echo area.
Argument ORIG-FUN is `message`.
Optional argument ARGS are the functions arguments."
  (if (or (string-empty-p echo-line--current) (active-minibuffer-window))
      ;; Regular log and display when minibuffer is active
      (apply orig-fun args)
    ;; Enhanced display
    (let* ((right-col-width (* echo-line-text-scale-factor
                               (string-width echo-line--current)))
           (raw-msg (if (and args (car args))
                        (apply 'format-message args)
                      ""))
           (msg (echo-line--process-message
                 raw-msg
                 (- (frame-width) right-col-width)))
           (full (concat msg
                         (propertize " "
                                     'echo-message-start t
                                     'display `((space
                                                 :align-to (- (+ right
                                                                 right-fringe
                                                                 right-margin)
                                                              ,right-col-width))))
                         echo-line--current)))
      ;; Log actual message without echo
      (when (and (not (string-empty-p raw-msg)) message-log-max)
        (let ((inhibit-message t))
          (funcall orig-fun "%s" raw-msg)))
      ;; Display enhanced message without log
      (let ((message-truncate-lines t) (message-log-max nil))
        (funcall orig-fun "%s" full))
      ;; Set current message explicitly.. Not really necessary.
      (setq current-message raw-msg))))

(defun echo-line--re-echo ()
  "Re-echo the current message to the echo-area."
  (let ((message-log-max nil)
        (msg (current-message)))
    (if msg
        (message "%s" msg)
      (message nil))))

(define-minor-mode echo-line-mode
  "Enables `echo-line-mode' globally."
  :require 'echo-line
  :init-value nil
  :global t
  (if (and echo-line-mode (display-graphic-p))
      (progn
        (advice-add 'message :around #'echo-line--message@advice)
        (add-hook 'post-command-hook #'echo-line--re-echo)
        (echo-line-update))
    (advice-remove 'message #'echo-line--message@advice)
    (remove-hook 'post-command-hook #'echo-line--re-echo)))

(provide 'echo-line)

;;; echo-line.el ends here

@overideal, thanks for bringing echo-bar to my attention. I somehow didn't know about it!
If anything, it seems to be the superior option compared to the above snippet. I switched to it just now and will test it out over the coming days/weeks.