patch 8.1.0349: crash when wiping buffer in a callback

Problem:    Crash when wiping buffer in a callback.
Solution:   Do not handle messages when only peeking for a character.
            (closes #2107)  Add "redraw_flag" to test_override().

runtime/doc/eval.txt

@@ -8737,6 +8737,7 @@ test_override({name}, {val})				*test_override()*
 
 		name	     effect when {val} is non-zero ~
 		redraw       disable the redrawing() function
+		redraw_flag  ignore the RedrawingDisabled flag
 		char_avail   disable the char_avail() function
 		starting     reset the "starting" variable, see below
 		nfa_fail     makes the NFA regexp engine fail to force a

src/evalfunc.c

@@ -13073,6 +13073,8 @@ f_test_override(typval_T *argvars, typval_T *rettv UNUSED)
 
 	if (STRCMP(name, (char_u *)"redraw") == 0)
 	    disable_redraw_for_testing = val;
+	else if (STRCMP(name, (char_u *)"redraw_flag") == 0)
+	    ignore_redraw_flag_for_testing = val;
 	else if (STRCMP(name, (char_u *)"char_avail") == 0)
 	    disable_char_avail_for_testing = val;
 	else if (STRCMP(name, (char_u *)"starting") == 0)
@@ -13095,6 +13097,7 @@ f_test_override(typval_T *argvars, typval_T *rettv UNUSED)
 	{
 	    disable_char_avail_for_testing = FALSE;
 	    disable_redraw_for_testing = FALSE;
+	    ignore_redraw_flag_for_testing = FALSE;
 	    nfa_fail_for_testing = FALSE;
 	    if (save_starting >= 0)
 	    {

src/globals.h

@@ -1633,9 +1633,10 @@ EXTERN int  alloc_fail_countdown INIT(= -1);
 EXTERN int  alloc_fail_repeat INIT(= 0);
 
 /* flags set by test_override() */
-EXTERN int  disable_char_avail_for_testing INIT(= 0);
-EXTERN int  disable_redraw_for_testing INIT(= 0);
-EXTERN int  nfa_fail_for_testing INIT(= 0);
+EXTERN int  disable_char_avail_for_testing INIT(= FALSE);
+EXTERN int  disable_redraw_for_testing INIT(= FALSE);
+EXTERN int  ignore_redraw_flag_for_testing INIT(= FALSE);
+EXTERN int  nfa_fail_for_testing INIT(= FALSE);
 
 EXTERN int  in_free_unref_items INIT(= FALSE);
 #endif

src/os_unix.c

@@ -417,10 +417,14 @@ mch_inchar(
 	    handle_resize();
 
 #ifdef MESSAGE_QUEUE
-	parse_queued_messages();
-	/* If input was put directly in typeahead buffer bail out here. */
-	if (typebuf_changed(tb_change_cnt))
-	    return 0;
+	// Only process messages when waiting.
+	if (wtime != 0)
+	{
+	    parse_queued_messages();
+	    // If input was put directly in typeahead buffer bail out here.
+	    if (typebuf_changed(tb_change_cnt))
+		return 0;
+	}
 #endif
 	if (wtime < 0 && did_start_blocking)
 	    /* blocking and already waited for p_ut */

src/os_win32.c

@@ -1529,15 +1529,19 @@ WaitForChar(long msec, int ignore_input)
      */
     for (;;)
     {
+	// Only process messages when waiting.
+	if (msec != 0)
+	{
 #ifdef MESSAGE_QUEUE
-	parse_queued_messages();
+	    parse_queued_messages();
 #endif
 #ifdef FEAT_MZSCHEME
-	mzvim_check_threads();
+	    mzvim_check_threads();
 #endif
 #ifdef FEAT_CLIENTSERVER
-	serverProcessPendingMessages();
+	    serverProcessPendingMessages();
 #endif
+	}
 
 	if (0
 #ifdef FEAT_MOUSE

src/screen.c

@@ -10819,8 +10819,11 @@ redrawing(void)
 	return 0;
     else
 #endif
-	return (!RedrawingDisabled
-		       && !(p_lz && char_avail() && !KeyTyped && !do_redraw));
+	return ((!RedrawingDisabled
+#ifdef FEAT_EVAL
+		    || ignore_redraw_flag_for_testing
+#endif
+		) && !(p_lz && char_avail() && !KeyTyped && !do_redraw));
 }
 
 /*

src/version.c

@@ -794,6 +794,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    349,
 /**/
     348,
 /**/