bug#34179: 27.0.50; message hangs when buffer with process visible

[martin rudalics <rudalics@gmx.at>]

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 >>> Michael, please check whether it fixes your
 >>> use case.
 >
 > That seems to be the case, yes.

Probably good to know.  Meanwhile, please try the attached patch which
should "cure" the underlying problem (it's the same as for Bug#34138).

It does not cure another problem I found this way based on your
scenario:

   With emacs -Q do M-x shell, C-x 5 2, and M-: (message "A\nB").

Here with emacs 25 this grows the minibuffer window and displays the
two lines

A
B

in it.  With emacs 26 it shortly resizes the minibuffer window and
then displays "A\nB" in it.  With patched master it displays

Eval: (message "A\nB")

with the cursor at the beginning of the minibuffer.

I have no idea yet what's causing these behaviors but so far the
presence of an external procees or shell looks like a necessary
prerequisite.  Ideas welcome.

Thanks, martin

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diff --git a/src/xdisp.c b/src/xdisp.c
index 8649507..ed4474e 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -14153,6 +14153,9 @@ static void debug_method_add (struct window *, char const *, ...)
       clear_garbaged_frames ();
     }
 
+  if (!NILP (Vrun_hooks))
+    run_window_change_functions ();
+
   if (windows_or_buffers_changed && !update_mode_lines)
     /* Code that sets windows_or_buffers_changed doesn't distinguish whether
        only the windows's contents needs to be refreshed, or whether the
@@ -14332,18 +14335,6 @@ static void debug_method_add (struct window *, char const *, ...)
 		  && (w = XWINDOW (selected_window)) != sw)
 		goto retry;
 
-	      if (!NILP (Vrun_hooks))
-		{
-		  run_window_change_functions ();
-
-		  /* If windows or buffers changed or selected_window
-		     changed, redisplay again.  */
-		  if ((windows_or_buffers_changed)
-		      || (WINDOWP (selected_window)
-			  && (w = XWINDOW (selected_window)) != sw))
-		    goto retry;
-		}
-
 		/* We used to always goto end_of_redisplay here, but this
 		 isn't enough if we have a blinking cursor.  */
 	      if (w->cursor_off_p == w->last_cursor_off_p)
@@ -14707,18 +14698,6 @@ static void debug_method_add (struct window *, char const *, ...)
 	  && (w = XWINDOW (selected_window)) != sw))
     goto retry;
 
-  if (!NILP (Vrun_hooks))
-    {
-      run_window_change_functions ();
-
-      /* If windows or buffers changed or selected_window changed,
-	 redisplay again.  */
-      if ((windows_or_buffers_changed)
-	  || (WINDOWP (selected_window)
-	      && (w = XWINDOW (selected_window)) != sw))
-	goto retry;
-    }
-
   /* Clear the face and image caches.
 
      We used to do this only if consider_all_windows_p.  But the cache