bug#43572: Feature request: make it possible to choose whether the first lines of the minibuffer should be displayed instead of the last ones

[Gregory Heytings via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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>> I can't believe this, in particular given that the default value of 
>> enable-recursive-minibuffers is nil.
>
> You again are thinking only about uses of mini-window for editing in the 
> minibuffer.  But that is not the only use of the mini-window.
>

I'm not sure I understand what you mean, but it seems to me that these 
other uses of the mini-window are not at all affected by the proposed 
patch, given that `start-display-at-beginning-of-minibuffer' is reset 
immediately when read_minibuf() / read-from-minibuffer has ended.

>
> And even in its use for the minibuffer, many users enable recursive 
> minibuffers.  I would not be surprised if some specialized modes and 
> packages enabled it for their operations.
>

If this case is important, the attached corrected patch also disables 
setting `start-display-at-beginning-of-minibuffer' in recursive 
minibuffers, that is, it limits the effect of that variable to 
non-recursive minibuffers.

I'll wait until you and Stefan agree on the way to solve that problem in a 
better way to start working on this.  In his last mail he is apparently 
not sure anymore that using text properties to do this, as he suggested 
yesterday, is the best solution.

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diff --git a/src/minibuf.c b/src/minibuf.c
index f957b2ae17..75ab82278b 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -472,6 +472,8 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
     = Fcons (Voverriding_local_map,
 	     Fcons (minibuf_window,
 		    minibuf_save_list));
+  minibuf_save_list
+    = Fcons (Vstart_display_at_beginning_of_minibuffer, minibuf_save_list);
   minibuf_save_list
     = Fcons (minibuf_prompt,
 	     Fcons (make_fixnum (minibuf_prompt_width),
@@ -659,6 +661,8 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
 
   run_hook (Qminibuffer_setup_hook);
 
+  if (minibuf_level > 1) Vstart_display_at_beginning_of_minibuffer = Qnil;
+
   /* Don't allow the user to undo past this point.  */
   bset_undo_list (current_buffer, Qnil);
 
@@ -802,6 +806,8 @@ read_minibuf_unwind (void)
   minibuf_save_list = Fcdr (minibuf_save_list);
   Vminibuffer_history_variable = Fcar (minibuf_save_list);
   minibuf_save_list = Fcdr (minibuf_save_list);
+  Vstart_display_at_beginning_of_minibuffer = Fcar (minibuf_save_list);
+  minibuf_save_list = Fcdr (minibuf_save_list);
   Voverriding_local_map = Fcar (minibuf_save_list);
   minibuf_save_list = Fcdr (minibuf_save_list);
 #if 0
@@ -2097,6 +2103,15 @@ syms_of_minibuf (void)
 uses to hide passwords.  */);
   Vread_hide_char = Qnil;
 
+  DEFVAR_LISP ("start-display-at-beginning-of-minibuffer", Vstart_display_at_beginning_of_minibuffer,
+	       doc: /* Whether to preferably display the beginning of the minibuffer.
+When the mini-window is not large enough to display the complete minibuffer,
+the default behavior is to display the last part of the minibuffer and to
+hide its first part.  This variable reverses that behavior when it is set
+in `minibuffer-setup-hook'.  It is reset before and after each read from
+the minibuffer, and unset in recursive minibuffers.  */);
+  Vstart_display_at_beginning_of_minibuffer = Qnil;
+
   defsubr (&Sactive_minibuffer_window);
   defsubr (&Sset_minibuffer_window);
   defsubr (&Sread_from_minibuffer);
diff --git a/src/xdisp.c b/src/xdisp.c
index 49225c56fe..1b1a34b97f 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -11804,7 +11804,7 @@ resize_mini_window (struct window *w, bool exact_p)
 	}
 
       /* Compute a suitable window start.  */
-      if (height > max_height)
+      if (height > max_height && !EQ (Vstart_display_at_beginning_of_minibuffer, Qt))
 	{
 	  height = (max_height / unit) * unit;
 	  init_iterator (&it, w, ZV, ZV_BYTE, NULL, DEFAULT_FACE_ID);
@@ -11812,7 +11812,10 @@ resize_mini_window (struct window *w, bool exact_p)
 	  start = it.current.pos;
 	}
       else
-	SET_TEXT_POS (start, BEGV, BEGV_BYTE);
+	{
+	  if (height > max_height) height = (max_height / unit) * unit;
+	  SET_TEXT_POS (start, BEGV, BEGV_BYTE);
+	}
 
       SET_MARKER_FROM_TEXT_POS (w->start, start);