--- a/icomplete.el	2020-09-01 10:14:22.000000000 +0000
+++ b/icomplete.el	2020-09-18 21:14:15.000000000 +0000
@@ -62,6 +62,10 @@
   :type 'string
   :version "24.4")
 
+(defcustom icomplete-vertical nil "...")
+
+(defvar icomplete--prospects-count 0 "...")
+
 (defcustom icomplete-hide-common-prefix t
   "When non-nil, hide common prefix from completion candidates.
 When nil, show candidates in full."
@@ -573,7 +577,10 @@
               ;; marker's stickiness to figure out whether to place the cursor
               ;; before or after the string, so let's spoon-feed it the pos.
               (put-text-property 0 1 'cursor t text)
-              (overlay-put icomplete-overlay 'after-string text))))))))
+              (overlay-put icomplete-overlay 'after-string text)
+	      (if (and (> (window-height) icomplete--prospects-count)
+		       (< icomplete--prospects-count icomplete-prospects-height))
+		  (shrink-window (- icomplete-prospects-height icomplete--prospects-count))))))))))
 
 ;;;_ > icomplete-completions (name candidates predicate require-match)
 (defun icomplete-completions (name candidates predicate require-match)
@@ -650,18 +657,22 @@
 				(t (concat ellipsis (substring most compare))))
 			       close-bracket)))
 	     ;;"-prospects" - more than one candidate
-	     (prospects-len (+ (string-width
-				(or determ (concat open-bracket close-bracket)))
-			       (string-width icomplete-separator)
-			       (+ 2 (string-width ellipsis)) ;; take {…} into account
-			       (string-width (buffer-string))))
+	     (prospects-len (if icomplete-vertical
+				0
+			      (+ (string-width
+				  (or determ (concat open-bracket close-bracket)))
+				 (string-width icomplete-separator)
+				 (+ 2 (string-width ellipsis)) ;; take {…} into account
+				 (string-width (buffer-string)))))
              (prospects-max
-              ;; Max total length to use, including the minibuffer content.
-              (* (+ icomplete-prospects-height
-                    ;; If the minibuffer content already uses up more than
-                    ;; one line, increase the allowable space accordingly.
-                    (/ prospects-len (window-width)))
-                 (window-width)))
+	      (if icomplete-vertical
+		  icomplete-prospects-height
+		;; Max total length to use, including the minibuffer content.
+		(* (+ icomplete-prospects-height
+                      ;; If the minibuffer content already uses up more than
+                      ;; one line, increase the allowable space accordingly.
+                      (/ prospects-len (window-width)))
+                   (window-width))))
              ;; Find the common prefix among `comps'.
              ;; We can't use the optimization below because its assumptions
              ;; aren't always true, e.g. when completion-cycling (bug#10850):
@@ -705,13 +716,20 @@
 	    (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 icomplete-vertical
+		(if (> (length comp) 0)
+		    (setq prospects-len (1+ prospects-len)))
+	      (setq prospects-len
+                    (+ (string-width comp)
+		       (string-width icomplete-separator)
+		       prospects-len)))
 	    (if (< prospects-len prospects-max)
-		(push comp prospects)
+		(if icomplete-vertical
+		    (if (> (length comp) 0)
+			(push comp prospects))
+		  (push comp prospects))
 	      (setq limit t))))
+	(setq icomplete--prospects-count prospects-len)
 	(setq prospects (nreverse prospects))
         ;; Return the first match if the user hits enter.
         (when icomplete-show-matches-on-no-input
@@ -726,11 +744,16 @@
         ;; 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