bug#38645: 26.3; minibuffer input is called with multi-line window when multi-line message is shown

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 38645@debbugs.gnu.org
> From: martin rudalics <rudalics@gmx.at>
> Date: Fri, 27 Dec 2019 10:12:33 +0100
> 
>  > Martin, what do you think about the following fix?  Is it correct, and
>  > if so, safe enough for the release branch?
> 
> It seems "correct" in the sense that our doc of 'resize-mini-windows'
> nowhere contradicts any such interpretation.  It should be "safe" in
> the sense that failing to always resize the minibuffer window exactly
> and falling back on 'grow-only' should not do any harm since otherwise
> we'd have a bug in the 'grow-only' part of the code.
> 
> But I'm too silly to understand why the minibuffer window does not
> re-grow in the first place after having shown the result of C-x C-e.
> Can you enlighten me?

I hope the following alternative patch will answer that question.
Comments are welcome.

diff --git a/src/keyboard.c b/src/keyboard.c
index 4cf1f64b48..a04f1f77de 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -1318,6 +1318,11 @@ command_loop_1 (void)
 	  message1 (0);
 	  safe_run_hooks (Qecho_area_clear_hook);
 
+	  /* We cleared the echo area, and the minibuffer will now
+	     show, so resize the mini-window in case the minibuffer
+	     needs more or less space than the echo area.  */
+	  resize_mini_window (XWINDOW (minibuf_window), false);
+
 	  unbind_to (count, Qnil);
 
 	  /* If a C-g came in before, treat it as input now.  */
@@ -2989,6 +2994,16 @@ read_char (int commandflag, Lisp_Object map,
 	{
 	  safe_run_hooks (Qecho_area_clear_hook);
 	  clear_message (1, 0);
+	  /* If we were showing the echo-area message on top of an
+	     active minibuffer, resize the mini-window, since the
+	     minibuffer may need more or less space than the echo area
+	     we've just wiped.  */
+	  if (minibuf_level
+	      && EQ (minibuf_window, echo_area_window)
+	      /* The case where minibuffer-message-timeout is a number
+		 was already handled near the beginning of this function.  */
+	      && !NUMBERP (Vminibuffer_message_timeout))
+	    resize_mini_window (XWINDOW (minibuf_window), false);
 	}
       else if (FUNCTIONP (Vclear_message_function))
         clear_message (1, 0);