* lisp/minibuffer.el (completions-format): Add new value 'one-column'.

* lisp/minibuffer.el (completion--insert-strings): Support 'one-column'.

* lisp/simple.el (read-from-kill-ring): Truncate strings at frame-width.

etc/NEWS

@@ -1345,6 +1345,9 @@ This new command (bound to 'C-c C-l') regenerates the current hunk.
 When non-nil, some commands like 'describe-symbol' show more detailed
 completions with more information in completion prefix and suffix.
 
+---
+*** User option 'completions-format' supports a new value 'one-column'.
+
 ---
 *** New user option 'bibtex-unify-case-convert'.
 This new option allows the user to customize how case is converted

lisp/minibuffer.el

@@ -1679,9 +1679,11 @@ Return nil if there is no valid completion, else t."
   "Define the appearance and sorting of completions.
 If the value is `vertical', display completions sorted vertically
 in columns in the *Completions* buffer.
-If the value is `horizontal', display completions sorted
-horizontally in alphabetical order, rather than down the screen."
-  :type '(choice (const horizontal) (const vertical))
+If the value is `horizontal', display completions sorted in columns
+horizontally in alphabetical order, rather than down the screen.
+If the value is `one-column', display completions down the screen
+in one column."
+  :type '(choice (const horizontal) (const vertical) (const one-column))
   :version "23.2")
 
 (defcustom completions-detailed nil
@@ -1727,6 +1729,9 @@ It also eliminates runs of equal strings."
                             (apply #'+ (mapcar #'string-width str))
                           (string-width str))))
             (cond
+             ((eq completions-format 'one-column)
+              ;; Nothing special
+              )
 	     ((eq completions-format 'vertical)
 	      ;; Vertical format
 	      (when (> row rows)
@@ -1790,6 +1795,8 @@ It also eliminates runs of equal strings."
                     (font-lock-prepend-text-property
                      beg end 'face 'completions-annotations)))))
 	    (cond
+             ((eq completions-format 'one-column)
+              (insert "\n"))
 	     ((eq completions-format 'vertical)
 	      ;; Vertical format
 	      (if (> column 0)

lisp/simple.el

@@ -5477,15 +5477,16 @@ With ARG, rotate that many kills forward (or backward, if negative)."
          (completions
           (mapcar (lambda (s)
                     (let* ((s (query-replace-descr s))
-                           (b 0))
+                           (b 0)
+                           (limit (frame-width)))
                       ;; Add ellipsis on leading whitespace
                       (when (string-match "\\`[[:space:]]+" s)
                         (setq b (match-end 0))
                         (add-text-properties 0 b `(display ,ellipsis) s))
                       ;; Add ellipsis at the end of a long string
-                      (when (> (length s) (+ 40 b))
+                      (when (> (length s) (+ limit b))
                         (add-text-properties
-                         (min (+ 40 b) (length s)) (length s)
+                         (min (+ limit b) (length s)) (length s)
                          `(display ,ellipsis) s))
                       s))
                   read-from-kill-ring-history)))