--- a/icomplete.el	2020-09-01 10:14:22.000000000 +0000
+++ b/icomplete.el	2020-09-19 03:54:43.000000000 +0000
@@ -62,6 +62,8 @@
   :type 'string
   :version "24.4")
 
+(defcustom icomplete-vertical nil "...")
+
 (defcustom icomplete-hide-common-prefix t
   "When non-nil, hide common prefix from completion candidates.
 When nil, show candidates in full."
@@ -107,6 +109,8 @@
   :type 'integer
   :version "26.1")
 
+(defvar icomplete--prospects-actual-height 0 "...")
+
 (defcustom icomplete-compute-delay .3
   "Completions-computation stall, used only with large-number completions.
 See `icomplete-delay-completions-threshold'."
@@ -431,6 +435,13 @@
   "Run in minibuffer on activation to establish incremental completion.
 Usually run by inclusion in `minibuffer-setup-hook'."
   (when (and icomplete-mode (icomplete-simple-completing-p))
+    (setq icomplete--prospects-actual-height
+	  (min icomplete-prospects-height
+	       (1- (floor (/ (* (if (floatp max-mini-window-height)
+				    (frame-native-height)
+				  (frame-char-height))
+				max-mini-window-height)
+			     (line-pixel-height))))))
     (set (make-local-variable 'completion-show-inline-help) nil)
     (use-local-map (make-composed-keymap icomplete-minibuffer-map
     					 (current-local-map)))
@@ -701,17 +712,30 @@
 	    ;; completion field.
 	    (setq determ (concat open-bracket "" close-bracket)))
 	  ;; Compute prospects for display.
-	  (while (and comps (not limit))
-	    (setq comp
-		  (if prefix-len (substring (car comps) prefix-len) (car comps))
-		  comps (cdr comps))
-	    (setq prospects-len
-                  (+ (string-width comp)
-		     (string-width icomplete-separator)
-		     prospects-len))
-	    (if (< prospects-len prospects-max)
-		(push comp prospects)
-	      (setq limit t))))
+	  (if icomplete-vertical
+	      (let ((prospects-len 0)
+		    (prospects-max (- icomplete--prospects-actual-height (/ (point) (window-width)))))
+		(while (and comps (not limit))
+		  (setq comp
+			(if prefix-len (substring (car comps) prefix-len) (car comps))
+			comps (cdr comps))
+		  (if (> (length comp) 0)
+		      (setq prospects-len (1+ prospects-len)))
+		  (if (< prospects-len prospects-max)
+		      (if (> (length comp) 0)
+			  (push comp prospects))
+		    (setq limit t))))
+	    (while (and comps (not limit))
+	      (setq comp
+		    (if prefix-len (substring (car comps) prefix-len) (car comps))
+		    comps (cdr comps))
+	      (setq prospects-len
+                    (+ (string-width comp)
+		       (string-width icomplete-separator)
+		       prospects-len))
+	      (if (< prospects-len prospects-max)
+		  (push comp prospects)
+		(setq limit t)))))
 	(setq prospects (nreverse prospects))
         ;; Return the first match if the user hits enter.
         (when icomplete-show-matches-on-no-input
@@ -726,11 +750,16 @@
         ;; is cached.
         (if last (setcdr last base-size))
 	(if prospects
-	    (concat determ
-		    "{"
-		    (mapconcat 'identity prospects icomplete-separator)
-		    (and limit (concat icomplete-separator ellipsis))
-		    "}")
+	    (if icomplete-vertical
+		(concat determ
+			" \n"
+			(mapconcat 'identity prospects "\n")
+			(and limit (concat "\n" ellipsis)))
+	      (concat determ
+		      "{"
+		      (mapconcat 'identity prospects icomplete-separator)
+		      (and limit (concat icomplete-separator ellipsis))
+		      "}"))
 	  (concat determ " [Matched]"))))))
 
 ;;; Iswitchb compatibility