bug#50038: Permanent shift-select-mode

[Juri Linkov]

>> +When the value is `permanent', the mark will not be deactivated
>> +by any subsequent point motion key that was not shift-translated.
>
> This is a negative description, which tells half of the story, and
> leaves it to the reader to guess the other half (how to deactivate the
> mark in this case).  How about describing both, and in a positive way?
> For example:
>
>   When the value is `permanent', the mark will be deactivated by any
>   action which normally does that, but not by motion keys that were
>   not shift-translated.

Fixed in the new patch.

> And finally, a question: is it enough to have this as a user option?
> That is, what if the user wants this only temporarily, for the next
> sequence of commands that extend the region?  Should we perhaps have a
> better solution for that use case?  More generally, perhaps this
> feature is almost always wanted only for a sequence of commands, never
> globally for extended periods of time?  In that case, a user option is
> not the best solution; it is better to have some minor mode that could
> be turned on and off with a simple key sequence.

It would be very surprising if someone might want something more complicated.
But everyone is welcome to extend this feature when such a need will arise.

>>  See `this-command-keys-shift-translated' for the meaning of
>>  shift-translation."
>> -  :type 'boolean
>> +  :type '(choice (const :tag "Off" nil)
>> +                 (const :tag "Permanent" permanent)
>> +                 (other :tag "On" t))
>> +  :version "28.1"
>>    :group 'editing-basics)
>
> This would also need a NEWS entry, if we eventually decide to do it
> this way.

This patch also adds a NEWS entry:

diff --git a/etc/NEWS b/etc/NEWS
index 09ace73f5d..37acef0be1 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -263,6 +263,12 @@ This works in text buffers and over images.  Typing a 
numeric prefix arg
 (e.g. 'M-5') before starting horizontal scrolling changes its step value.
 The value is saved in the user option 'mouse-wheel-scroll-amount-horizontal'.
 
+---
+** New choice 'permanent' for 'shift-select-mode'.
+When the mark was activated by shifted motion keys,
+non-shifted motion keys don't deactivate the mark
+after customizing 'shift-select-mode' to 'permanent'.
+
 ---
 ** The default value of 'frame-title-format' and 'icon-title-format' has 
changed.
 These variables are used to display the title bar of visible frames
diff --git a/lisp/simple.el b/lisp/simple.el
index 985beb06fc..960422a6b2 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -6649,9 +6649,16 @@ shift-select-mode
 by any subsequent point motion key that was not shift-translated, or
 by any action that normally deactivates the mark in Transient Mark mode.
 
+When the value is `permanent', the mark will be deactivated by any
+action which normally does that, but not by motion keys that were
+not shift-translated.
+
 See `this-command-keys-shift-translated' for the meaning of
 shift-translation."
-  :type 'boolean
+  :type '(choice (const :tag "Off" nil)
+                 (const :tag "Permanent" permanent)
+                 (other :tag "On" t))
+  :version "28.1"
   :group 'editing-basics)
 
 (defun handle-shift-selection ()
@@ -6669,7 +6676,12 @@ handle-shift-selection
 Otherwise, if the region has been activated temporarily,
 deactivate it, and restore the variable `transient-mark-mode' to
 its earlier value."
-  (cond ((and shift-select-mode this-command-keys-shift-translated)
+  (cond ((and (eq shift-select-mode 'permanent)
+              this-command-keys-shift-translated)
+         (unless mark-active
+           (push-mark nil nil t)))
+        ((and shift-select-mode
+              this-command-keys-shift-translated)
          (unless (and mark-active
                      (eq (car-safe transient-mark-mode) 'only))
           (setq-local transient-mark-mode