Re: Navigating completions from minibuffer

[Spencer Baugh]

Juri Linkov <juri@linkov.net> writes:
>> minibuffer-choose-completion-or-exit submits the selected completion
>> candidate, if any, ignoring the contents of the minibuffer.  But a
>> user might select a completion candidate and then want to type
>> something else in the minibuffer and submit what they typed.
>
> Thanks, everything works nicely now except the special case
> of completion-show-help=nil and completions-header-format=nil.
>
> Initially the first completion is deselected, and <down> selects it.
> But when the first key typed is M-<down> the second completion
> is selected instead of the first because M-<down> moves to the
> second column when point is between the first and second completions.

I was thinking that issue is unrelated to this patch and so it could be
fixed separately.  But actually I guess this patch makes it more visible
indeed, so I guess we need to fix it now.

I think the "add a thin newline" approach is totally fine.  I did that
in my attached patch.

> A possible workaround would be to check the special property
> 'first-completion'.  But then when the logic uses text properties,
> why not to use more text properties that indicate that a candidate
> is deselected (and remove highlighting in this case) instead of
> moving point somewhere outside of the candidate?

Even if we work around this with text properties, I think it's nice for
deselection to be usually determined by location of point.  I think
that's easier to understand for the user - they should be able to
deselect or reselect something purely by moving point around, it
shouldn't require text property manipulation.

>From f4e2bdda0e30af933bee896aa7b5ca2b22684ab5 Mon Sep 17 00:00:00 2001
From: Spencer Baugh <sbaugh@catern.com>
Date: Thu, 23 Nov 2023 13:37:29 +0000
Subject: [PATCH] Deselect the selected completion candidate when typing

minibuffer-choose-completion-or-exit submits the selected completion
candidate, if any, ignoring the contents of the minibuffer.  But a
user might select a completion candidate and then want to type
something else in the minibuffer and submit what they typed.

Now typing will automatically deselect the selected completion
candidate so that minibuffer-choose-completion-or-exit will not choose
it.

minibuffer-choose-completion has the same behavior as before, and is
not affected by the deselection.

* lisp/minibuffer.el (completion-auto-deselect, completions--deselect)
(completions--after-change): Add.
(minibuffer-completion-help): Add completions--after-change hook.
(minibuffer-next-completion): Bind completion-auto-deselect to nil to
avoid immediately deselecting the completion.
(minibuffer-choose-completion-or-exit): Bind
choose-completion-deselect-if-after so deselection takes effect.
(display-completion-list): Guarantee a newline at the beginning of
*Completions* to avoid ambiguity about candidate selection.
* lisp/simple.el (choose-completion-deselect-if-after): Add.
(choose-completion): Check choose-completion-deselect-if-after.
---
 lisp/minibuffer.el | 43 +++++++++++++++++++++++++++++++++++++++----
 lisp/simple.el     | 11 ++++++++++-
 2 files changed, 49 insertions(+), 5 deletions(-)

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 5c12d9fc914..303170125ff 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -2310,8 +2310,11 @@ display-completion-list
 
     (with-current-buffer standard-output
       (goto-char (point-max))
-      (when completions-header-format
-        (insert (format completions-header-format (length completions))))
+      (if completions-header-format
+          (insert (format completions-header-format (length completions)))
+        (unless completion-show-help
+          ;; Ensure beginning-of-buffer isn't a completion.
+          (insert (propertize "\n" 'face '(:height 0)))))
       (completion--insert-strings completions group-fun)))
 
   (run-hooks 'completion-setup-hook)
@@ -2378,6 +2381,33 @@ completions--fit-window-to-buffer
         (resize-temp-buffer-window win))
     (fit-window-to-buffer win completions-max-height)))
 
+(defcustom completion-auto-deselect t
+  "If non-nil, deselect the selected completion candidate when you type.
+
+A non-nil value means that after typing, point in *Completions*
+will be moved off any completion candidates.  This means
+`minibuffer-choose-completion-or-exit' will exit with the
+minibuffer's current contents, instead of a completion candidate."
+  :type '(choice (const :tag "Candidates in *Completions* stay selected as you 
type" nil)
+                 (const :tag "Typing deselects any completion candidate in 
*Completions*" t))
+  :version "30.1")
+
+(defun completions--deselect ()
+  "If point is in a completion candidate, move to just after the end of it.
+
+The candidate will still be chosen by `choose-completion' unless
+`choose-completion-deselect-if-after' is non-nil."
+  (when (get-text-property (point) 'mouse-face)
+    (goto-char (or (next-single-property-change (point) 'mouse-face)
+                   (point-max)))))
+
+(defun completions--after-change (_start _end _old-len)
+  "Update displayed *Completions* buffer after change in buffer contents."
+  (when completion-auto-deselect
+    (when-let (window (get-buffer-window "*Completions*" 0))
+      (with-selected-window window
+        (completions--deselect)))))
+
 (defun minibuffer-completion-help (&optional start end)
   "Display a list of possible completions of the current minibuffer contents."
   (interactive)
@@ -2400,6 +2430,7 @@ minibuffer-completion-help
           ;; If there are no completions, or if the current input is already
           ;; the sole completion, then hide (previous&stale) completions.
           (minibuffer-hide-completions)
+          (remove-hook 'after-change-functions #'completions--after-change t)
           (if completions
               (completion--message "Sole completion")
             (unless completion-fail-discreetly
@@ -2460,6 +2491,8 @@ minibuffer-completion-help
             (body-function
              . ,#'(lambda (_window)
                     (with-current-buffer mainbuf
+                      (when completion-auto-deselect
+                        (add-hook 'after-change-functions 
#'completions--after-change t))
                       ;; Remove the base-size tail because `sort' requires a 
properly
                       ;; nil-terminated list.
                       (when last (setcdr last nil))
@@ -4673,7 +4706,8 @@ minibuffer-next-completion
           (next-line-completion (or n 1))
         (next-completion (or n 1)))
       (when auto-choose
-        (let ((completion-use-base-affixes t))
+        (let ((completion-use-base-affixes t)
+              (completion-auto-deselect nil))
           (choose-completion nil t t))))))
 
 (defun minibuffer-previous-completion (&optional n)
@@ -4721,7 +4755,8 @@ minibuffer-choose-completion-or-exit
 contents."
   (interactive "P")
   (condition-case nil
-      (minibuffer-choose-completion no-exit no-quit)
+      (let ((choose-completion-deselect-if-after t))
+        (minibuffer-choose-completion no-exit no-quit))
     (error (minibuffer-complete-and-exit))))
 
 (defun minibuffer-complete-history ()
diff --git a/lisp/simple.el b/lisp/simple.el
index 02c68912dba..bf57b285fca 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -10094,6 +10094,11 @@ next-line-completion
           (if pos (goto-char pos))))
       (setq n (1+ n)))))
 
+(defvar choose-completion-deselect-if-after nil
+  "If non-nil, don't choose a completion candidate if point is right after it.
+
+This makes `completions--deselect' effective.")
+
 (defun choose-completion (&optional event no-exit no-quit)
   "Choose the completion at point.
 If EVENT, use EVENT's position to determine the starting position.
@@ -10114,6 +10119,10 @@ choose-completion
           (insert-function completion-list-insert-choice-function)
           (completion-no-auto-exit (if no-exit t completion-no-auto-exit))
           (choice
+           (if choose-completion-deselect-if-after
+               (if-let ((str (get-text-property (posn-point (event-start 
event)) 'completion--string)))
+                   (substring-no-properties str)
+                 (error "No completion here"))
            (save-excursion
              (goto-char (posn-point (event-start event)))
              (let (beg)
@@ -10129,7 +10138,7 @@ choose-completion
                               beg 'completion--string)
                              beg))
                (substring-no-properties
-                (get-text-property beg 'completion--string))))))
+                (get-text-property beg 'completion--string)))))))
 
       (unless (buffer-live-p buffer)
         (error "Destination buffer is dead"))
-- 
2.42.1