bug#62700: 29.0.60; minibuffer-{previous,next,choose}-completion behave unintuitively when point is not at end of buffer

[Juri Linkov]

> For example, with (setq completion-use-base-affixes t)
> if there is some text in the current buffer after point,
> then typing 'M-C-i' and selecting a candidate to insert to the buffer,
> it replaces all the text after point with an empty string.
>
> Before this change, the suffix was set to the text after point,
> and after inserting the selected candidate the suffix was
> re-inserted to the same buffer.

Here is a patch that should support 'completion-in-region':

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 07a284134d6..a2d0fabd9c5 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -2405,9 +2410,14 @@ minibuffer-completion-help
              (base-prefix (buffer-substring (minibuffer--completion-prompt-end)
                                             (+ start base-size)))
              (base-suffix
-              (if (eq (alist-get 'category (cdr md)) 'file)
-                  (buffer-substring (save-excursion (or (search-forward "/" 
nil t) (point-max)))
-                                    (point-max))
+              (if (or (eq (alist-get 'category (cdr md)) 'file)
+                      completion-in-region-mode-predicate)
+                  (buffer-substring
+                   (save-excursion
+                     (if completion-in-region-mode-predicate
+                         (point)
+                       (or (search-forward "/" nil t) (point-max))))
+                   (point-max))
                 ""))
              (all-md (completion--metadata (buffer-substring-no-properties
                                             start (point))