Allow for next-completion to wrap around the completion buffer

* lisp/simple.el (completion-wrap-movement): Add new option.
(previous-completion): Update docstring.
(next-completion): Respect completion-wrap-movement.
(switch-to-completions): Handle backwards completion by jumping to the
end of the buffer.
* lisp/minibuffer.el: (minibuffer-local-completion-map): Bind
minibuffer-complete to backtab
(completion--in-region-1): Handle backtab to scroll backwards

2 files changed, 74 insertions, 33 deletions

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 28bd1df59ab..112c609a0a1 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -1379,14 +1379,18 @@ scroll the window of possible completions."
    ;; and this command is repeated, scroll that window.
    ((and (window-live-p minibuffer-scroll-window)
          (eq t (frame-visible-p (window-frame minibuffer-scroll-window))))
-    (let ((window minibuffer-scroll-window))
+    (let ((window minibuffer-scroll-window)
+          (reverse (equal (this-command-keys) [backtab])))
       (with-current-buffer (window-buffer window)
-        (if (pos-visible-in-window-p (point-max) window)
-            ;; If end is in view, scroll up to the beginning.
-            (set-window-start window (point-min) nil)
+        (if (pos-visible-in-window-p (if reverse (point-min) (point-max)) window)
+            ;; If end or beginning is in view, scroll up to the
+            ;; beginning or end respectively.
+            (if reverse
+                (set-window-point window (point-max))
+              (set-window-start window (point-min) nil))
           ;; Else scroll down one screen.
           (with-selected-window window
-            (scroll-up)))
+            (if reverse (scroll-down) (scroll-up))))
         nil)))
    ;; If we're cycling, keep on cycling.
    ((and completion-cycling completion-all-sorted-completions)
@@ -2651,6 +2655,7 @@ The completion method is determined by `completion-at-point-functions'."
   (let ((map (make-sparse-keymap)))
     (set-keymap-parent map minibuffer-local-map)
     (define-key map "\t" 'minibuffer-complete)
+    (define-key map [backtab] 'minibuffer-complete)
     ;; M-TAB is already abused for many other purposes, so we should find
     ;; another binding for it.
     ;; (define-key map "\e\t" 'minibuffer-force-complete)
diff --git a/lisp/simple.el b/lisp/simple.el
index 62a9f264d67..e2d140af891 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -9029,38 +9029,68 @@ Go to the window from which completion was requested."
       (if (get-buffer-window buf)
           (select-window (get-buffer-window buf))))))
 
+(defcustom completion-wrap-movement t
+  "Non-nil means to wrap around when selecting completion options.
+This affects the commands `next-completion' and
+`previous-completion'."
+  :type 'boolean
+  :version "29.1"
+  :group 'completion)
+
 (defun previous-completion (n)
-  "Move to the previous item in the completion list."
+  "Move to the previous item in the completion list.
+With prefix argument N, move back N items (negative N means move
+forward)."
   (interactive "p")
   (next-completion (- n)))
 
 (defun next-completion (n)
   "Move to the next item in the completion list.
-With prefix argument N, move N items (negative N means move backward)."
+With prefix argument N, move N items (negative N means move
+backward)."
   (interactive "p")
   (let ((beg (point-min)) (end (point-max)))
-    (while (and (> n 0) (not (eobp)))
-      ;; If in a completion, move to the end of it.
-      (when (get-text-property (point) 'mouse-face)
-        (goto-char (next-single-property-change (point) 'mouse-face nil end)))
-      ;; Move to start of next one.
-      (unless (get-text-property (point) 'mouse-face)
-        (goto-char (next-single-property-change (point) 'mouse-face nil end)))
-      (setq n (1- n)))
-    (while (and (< n 0) (not (bobp)))
-      (let ((prop (get-text-property (1- (point)) 'mouse-face)))
-        ;; If in a completion, move to the start of it.
-        (when (and prop (eq prop (get-text-property (point) 'mouse-face)))
-          (goto-char (previous-single-property-change
-                      (point) 'mouse-face nil beg)))
-        ;; Move to end of the previous completion.
-        (unless (or (bobp) (get-text-property (1- (point)) 'mouse-face))
-          (goto-char (previous-single-property-change
-                      (point) 'mouse-face nil beg)))
-        ;; Move to the start of that one.
-        (goto-char (previous-single-property-change
-                    (point) 'mouse-face nil beg))
-        (setq n (1+ n))))))
+    (catch 'bound
+      (while (> n 0)
+        ;; If in a completion, move to the end of it.
+        (when (get-text-property (point) 'mouse-face)
+          (goto-char (next-single-property-change (point) 'mouse-face nil end)))
+        ;; If at the last completion option, wrap or skip to the
+        ;; minibuffer, if requested.
+        (when (and completion-wrap-movement (eobp))
+          (if (and (member (this-command-keys) '("\t" [backtab]))
+                   completion-auto-select)
+              (throw 'bound nil)
+            (goto-char (point-min))))
+        ;; Move to start of next one.
+        (unless (get-text-property (point) 'mouse-face)
+          (goto-char (next-single-property-change (point) 'mouse-face nil end)))
+        (setq n (1- n)))
+      (while (< n 0)
+        (let ((prop (get-text-property (1- (point)) 'mouse-face)))
+          ;; If in a completion, move to the start of it.
+          (when (and prop (eq prop (get-text-property (point) 'mouse-face)))
+            (goto-char (previous-single-property-change
+                        (point) 'mouse-face nil beg)))
+          ;; Move to end of the previous completion.
+          (unless (or (bobp) (get-text-property (1- (point)) 'mouse-face))
+            (goto-char (previous-single-property-change
+                        (point) 'mouse-face nil beg)))
+          ;; If at the first completion option, wrap or skip to the
+          ;; minibuffer, if requested.
+          (when (and completion-wrap-movement (bobp))
+            (if (and (member (this-command-keys) '("\t" [backtab]))
+                     completion-auto-select)
+                (progn
+                  (goto-char (next-single-property-change (point) 'mouse-face nil end))
+                  (throw 'bound nil))
+              (goto-char (point-max))))
+          ;; Move to the start of that one.
+          (goto-char (previous-single-property-change
+                      (point) 'mouse-face nil beg))
+          (setq n (1+ n)))))
+    (when (/= 0 n)
+      (switch-to-minibuffer))))
 
 (defun choose-completion (&optional event)
   "Choose the completion at point.
@@ -9285,10 +9315,16 @@ select the completion near point.\n\n")))))
                            (get-buffer-window "*Completions*" 0)))))
     (when window
       (select-window window)
-      ;; In the new buffer, go to the first completion.
-      ;; FIXME: Perhaps this should be done in `minibuffer-completion-help'.
-      (when (bobp)
-        (next-completion 1)))))
+      (cond
+       ((and (memq this-command '(completion-at-point minibuffer-complete))
+             (equal (this-command-keys) [backtab])
+             (bobp))
+        (goto-char (point-max))
+        (previous-completion 1))
+       ;; In the new buffer, go to the first completion.
+       ;; FIXME: Perhaps this should be done in `minibuffer-completion-help'.
+       ((bobp)
+        (next-completion 1))))))
 
 (defun read-expression-switch-to-completions ()
   "Select the completion list window while reading an expression."