From fb9a2b45b97712dba1f622f6dff7a84696b0f71d Mon Sep 17 00:00:00 2001
From: Gregory Heytings <gregory@heytings.org>
Date: Mon, 5 Apr 2021 21:30:26 +0000
Subject: [PATCH] Add an icomplete-vertical minor mode

* lisp/icomplete.el (icomplete-vertical-mode): New minor mode.
(icomplete-vertical-reformat-completions,
icomplete-vertical-minibuffer-setup): Auxiliary functions for the
new minor mode.

* etc/NEWS: Mention the new minor mode.

* doc/emacs/buffers.texi: Document the new minor mode.
---
 doc/emacs/buffers.texi |  5 ++++-
 etc/NEWS               |  7 +++++++
 lisp/icomplete.el      | 40 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/doc/emacs/buffers.texi b/doc/emacs/buffers.texi
index 3a166e404a..5561a704ca 100644
--- a/doc/emacs/buffers.texi
+++ b/doc/emacs/buffers.texi
@@ -740,7 +740,10 @@ Icomplete
 
   To enable Icomplete mode, type @kbd{M-x icomplete-mode}, or customize
 the variable @code{icomplete-mode} to @code{t} (@pxref{Easy
-Customization}).
+Customization}).  This will display the list of possible completions
+on the same line as the prompt.  To display the completion candidates
+vertically under the prompt instead, type @kbd{M-x icomplete-vertical-mode},
+or customize the variable @code{icomplete-vertical-mode} to @code{t}.
 
 @findex fido-mode
 @cindex fido mode
diff --git a/etc/NEWS b/etc/NEWS
index c8400ba8c2..cbce41d29d 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -477,6 +477,13 @@ 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 based on and identical to Icomplete, except that it displays
+the list of completions candidates vertically.
+
 ---
 ** 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 da589c0064..87b3431079 100644
--- a/lisp/icomplete.el
+++ b/lisp/icomplete.el
@@ -562,6 +562,46 @@ icomplete--sorted-completions
                  (completion--cache-all-sorted-completions beg end (cons comp all))))
        finally return all)))
 
+(defun icomplete-vertical-reformat-completions (completions)
+  "Reformat the completion candidates returned by `icomplete-completions'."
+  (save-match-data
+    (if (string-match "^\\((.*)\\|\\[.*\\]\\)?{\\(\\(?:.\\|\n\\)+\\)}"
+                      completions)
+        (format "%s \n%s"
+                (or (match-string 1 completions) "")
+                (match-string 2 completions))
+      completions)))
+
+(defun icomplete-vertical-minibuffer-setup ()
+  "Setup the minibuffer for vertical display of completion candidates."
+  (setq-local redisplay-adhoc-scroll-in-resize-mini-windows nil))
+
+;;;###autoload
+(define-minor-mode icomplete-vertical-mode
+  "Toggle incremental minibuffer completion with vertical display.
+
+This global minor mode is identical to `icomplete-mode' (which see),
+except that it displays the list of completions candidates vertically.
+
+As many completion candidates as possible are displayed, depending on
+the value of `max-mini-window-height'."
+  :global t :group 'icomplete
+  (remove-hook 'icomplete-minibuffer-setup-hook
+               #'icomplete-vertical-minibuffer-setup)
+  (advice-remove 'icomplete-completions
+                 #'icomplete-vertical-reformat-completions)
+  (icomplete-mode -1)
+  (when icomplete-vertical-mode
+    (icomplete-mode 1)
+    (setq icomplete-separator "\n")
+    (setq icomplete-hide-common-prefix nil)
+    ;; ask `icomplete-completions' to return enough completions candidates
+    (setq icomplete-prospects-height 25)
+    (add-hook 'icomplete-minibuffer-setup-hook
+              #'icomplete-vertical-minibuffer-setup)
+    (advice-add 'icomplete-completions
+                :filter-return #'icomplete-vertical-reformat-completions)))
+
 
 
 
-- 
2.30.2