From d0899b748b0047e1d1c773b06076faeba2535fee Mon Sep 17 00:00:00 2001
From: Philip Kaludercic <philipk@posteo.net>
Date: Sat, 17 Sep 2022 16:52:01 +0200
Subject: [PATCH] Add a quick-help menu

* lisp/help.el (help-map): Bind 'help-quit-or-quick' instead of 'help-quit'
(help-quick-sections): Add variable.
(help-quick): Add main command.
(help-quit-or-quick): Add auxiliary command.
---
 lisp/help.el | 109 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 108 insertions(+), 1 deletion(-)

diff --git a/lisp/help.el b/lisp/help.el
index 92b87cf799..089db8c2dd 100644
--- a/lisp/help.el
+++ b/lisp/help.el
@@ -112,7 +112,7 @@ help-map
     (define-key map "v" 'describe-variable)
     (define-key map "w" 'where-is)
     (define-key map "x" 'describe-command)
-    (define-key map "q" 'help-quit)
+    (define-key map "q" 'help-quit-or-quick)
     map)
   "Keymap for characters following the Help key.")
 
@@ -125,11 +125,118 @@ global-map
 (defvar help-button-cache nil)
 
 
+
+(defvar help-quick-sections
+  '(("FILE"
+     (save-buffers-kill-terminal . "exit")
+     (find-file . "find")
+     (write-file . "write")
+     (save-buffer . "save")
+     (save-some-buffers . "all"))
+    ("BUFFER"
+     (kill-buffer . "kill")
+     (list-buffers . "list")
+     (switch-to-buffer . "switch")
+     (goto-line . "goto line")
+     (read-only-mode . "read only"))
+    ("WINDOW"
+     (delete-window . "only other")
+     (delete-other-windows . "only this")
+     (split-window-below . "split vert.")
+     (split-window-right . "split horiz.")
+     (other-window . "other"))
+    ("MARK/KILL"
+     (set-mark-command . "mark")
+     (kill-region . "wipe")
+     (kill-line . "kill")
+     (yank . "yank")
+     (exchange-point-and-mark . "swap"))
+    ("PROJECT"
+     (project-switch-project . "switch")
+     (project-find-file . "find file")
+     (project-find-regexp . "search")
+     (project-query-replace-regexp . "replace")
+     (project-compile . "compile"))
+    ("MISC"
+     (undo . "undo")
+     (isearch-forward . "search")
+     (isearch-backward . "rev-search")
+     (query-replace . "replace")
+     (fill-paragraph . "reformat"))))
+
+;; Inspired by a mg fork (https://github.com/troglobit/mg)
+(defun help-quick ()
+  "Display a quick-help buffer."
+  (interactive)
+  (with-current-buffer (get-buffer-create "*Quick Help*")
+    (let ((inhibit-read-only t) (padding 2) blocks)
+
+      ;; Go through every section and prepare a text-rectangle to be
+      ;; inserted later.
+      (dolist (section help-quick-sections)
+        (let ((max-key-len 0) (max-cmd-len 0) keys)
+          (dolist (ent (reverse (cdr section)))
+            (let* ((bind (where-is-internal (car ent) nil t))
+                   (key (if bind
+                            (propertize
+                             (key-description bind)
+                             'face 'help-key-binding)
+                          (propertize "N.B." 'face 'error))))
+              (setq max-cmd-len (max (length (cdr ent)) max-cmd-len)
+                    max-key-len (max (length key) max-key-len))
+              (push (cons key (cdr ent)) keys)))
+          (let ((fmt (format "%%-%ds %%-%ds%s" max-key-len max-cmd-len
+                             (make-string padding ?\s)))
+                (width (+ max-key-len 1 max-cmd-len padding)))
+            (push `(,width
+                    ,(propertize
+                      (concat
+                       (car section)
+                       (make-string (- width (length (car section))) ?\s))
+                      'face 'bold)
+                    ,@(mapcar (lambda (ent)
+                                (format fmt (car ent) (cdr ent)))
+                              keys))
+                  blocks))))
+
+      ;; Insert each rectangle in order until they don't fit into the
+      ;; frame any more, in which case the next sections are inserted
+      ;; in a new "line".
+      (erase-buffer)
+      (dolist (block (nreverse blocks))
+        (when (> (+ (car block) (current-column)) (frame-width))
+          (goto-char (point-max))
+          (newline 2))
+        (save-excursion
+          (insert-rectangle (cdr block)))
+        (end-of-line))
+      (delete-trailing-whitespace))
+
+    ;; Display the buffer at the bottom of the page and shrink it
+    ;; immediately.
+    (help-mode)
+    (with-selected-window (display-buffer-at-bottom (current-buffer) '())
+      (fit-window-to-buffer))
+    (message
+     (substitute-command-keys "Toggle the quick help buffer using \\[help-quit-or-quick]."))))
+
 (defun help-quit ()
   "Just exit from the Help command's command loop."
   (interactive)
   nil)
 
+(defun help-quit-or-quick ()
+  "Call `help-quit' or  `help-quick' depending on the context."
+  (interactive)
+  (cond
+   (help-buffer-under-preparation
+    ;; FIXME: There should be a better way to detect if we are in the
+    ;;        help command loop.
+    (help-quit))
+   ((and-let* ((window (get-buffer-window "*Quick Help*")))
+      (quit-window t window)))
+   ((help-quick))))
+
 (defvar help-return-method nil
   "What to do to \"exit\" the help buffer.
 This is a list
-- 
2.37.3