Add new icomplete-vertical-modescratch/icomplete-vertical-mode-gregory-and-joao

Co-authored-by: João Távora <joaotavora@gmail.com>

* lisp/icomplete.el (icomplete-completions): Consider icomplete-vertical-mode.
(icomplete-vertical-mode-minibuffer-map): New map.
(icomplete--vertical-minibuffer-setup): New helper.
(icomplete-vertical-mode): New minor mode.

* doc/emacs/buffers.texi (Icomplete): Mention icomplete-vertical-mode.

* etc/NEWS: Mention icomplete-vertical-mode

3 files changed, 54 insertions, 4 deletions

diff --git a/doc/emacs/buffers.texi b/doc/emacs/buffers.texi
index 3a166e404a8..bec7f37547c 100644
--- a/doc/emacs/buffers.texi
+++ b/doc/emacs/buffers.texi
@@ -765,6 +765,15 @@ your initialization file (@pxref{Init File}):
 the variable @code{fido-mode} to @code{t} (@pxref{Easy
 Customization}).
 
+@findex icomplete-vertical-mode
+@cindex Icomplete vertical mode
+
+  Icomplete mode and Fido mode display the possible completions on the
+same line as the prompt by default.  To display the completion candidates
+vertically under the prompt, type @kbd{M-x icomplete-vertical-mode}, or
+customize the variable @code{icomplete-vertical-mode} to @code{t}
+(@pxref{Easy Customization}).
+
 @node Buffer Menus
 @subsection Customizing Buffer Menus
 
diff --git a/etc/NEWS b/etc/NEWS
index a0f05d8cf15..7fae0b7cfef 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -483,6 +483,13 @@ documented.
 SMIE is now always enabled and 'ruby-use-smie' only controls whether
 indentation is done using SMIE or with the old ad-hoc code.
 
+** Icomplete
+
++++
+*** New minor mode Icomplete-Vertical mode.
+This mode is intended to be used with Icomplete or Fido, to display the
+list of completions candidates vertically instead of horizontally.
+
 ---
 ** Specific warnings can now be disabled from the warning buffer.
 When a warning is displayed to the user, the resulting buffer now has
diff --git a/lisp/icomplete.el b/lisp/icomplete.el
index da589c00649..d5b6f76d7b2 100644
--- a/lisp/icomplete.el
+++ b/lisp/icomplete.el
@@ -562,6 +562,37 @@ Usually run by inclusion in `minibuffer-setup-hook'."
                  (completion--cache-all-sorted-completions beg end (cons comp all))))
        finally return all)))
 
+(defvar icomplete-vertical-mode-minibuffer-map
+  (let ((map (make-sparse-keymap)))
+    (define-key map (kbd "C-n") 'icomplete-forward-completions)
+    (define-key map (kbd "C-p") 'icomplete-backward-completions)
+    map)
+  "Keymap used by `icomplete-vertical-mode' in the minibuffer.")
+
+(defun icomplete--vertical-minibuffer-setup ()
+  "Setup the minibuffer for vertical display of completion candidates."
+  (use-local-map (make-composed-keymap icomplete-vertical-mode-minibuffer-map
+                                       (current-local-map)))
+  (setq-local icomplete-separator "\n"
+              icomplete-hide-common-prefix nil
+              ;; Ask `icomplete-completions' to return enough completions candidates.
+              icomplete-prospects-height 25
+              redisplay-adhoc-scroll-in-resize-mini-windows nil))
+
+;;;###autoload
+(define-minor-mode icomplete-vertical-mode
+  "Toggle vertical candidate display in `icomplete-mode' or `fido-mode'.
+
+As many completion candidates as possible are displayed, depending on
+the value of `max-mini-window-height', and the way the mini-window is
+resized depends on `resize-mini-windows'."
+  :global t
+  (remove-hook 'icomplete-minibuffer-setup-hook
+               #'icomplete--vertical-minibuffer-setup)
+  (when icomplete-vertical-mode
+    (add-hook 'icomplete-minibuffer-setup-hook
+              #'icomplete--vertical-minibuffer-setup)))
+
 
 
 
@@ -784,10 +815,13 @@ matches exist."
         (if last (setcdr last base-size))
 	(if prospects
 	    (concat determ
-		    "{"
-		    (mapconcat 'identity prospects icomplete-separator)
-		    (and limit (concat icomplete-separator ellipsis))
-		    "}")
+		    (if icomplete-vertical-mode " \n" "{")
+		    (mapconcat 'identity prospects (if icomplete-vertical-mode
+                                                       "\n"
+                                                       icomplete-separator))
+		    (unless icomplete-vertical-mode
+                      (concat (and limit (concat icomplete-separator ellipsis))
+                              "}")))
 	  (concat determ " [Matched]"))))))
 
 ;;; Iswitchb compatibility