patch 8.0.0592: if a job writes to a buffer screen is not updated

Problem:    If a job writes to a buffer and the user is typing a command, the
            screen isn't updated. When a message is displayed the changed
            buffer may cause it to be cleared. (Ramel Eshed)
Solution:   Update the screen and then the command line if the screen didn't
            scroll. Avoid inserting screen lines, as it clears any message.
            Update the status line when the buffer changed.

src/screen.c

@@ -265,6 +265,21 @@ redraw_buf_later(buf_T *buf, int type)
     }
 }
 
+    void
+redraw_buf_and_status_later(buf_T *buf, int type)
+{
+    win_T	*wp;
+
+    FOR_ALL_WINDOWS(wp)
+    {
+	if (wp->w_buffer == buf)
+	{
+	    redraw_win_later(wp, type);
+	    wp->w_redr_status = TRUE;
+	}
+    }
+}
+
 /*
  * Redraw as soon as possible.  When the command line is not scrolled redraw
  * right away and restore what was on the command line.
@@ -421,10 +436,29 @@ redraw_after_callback(void)
     if (State == HITRETURN || State == ASKMORE)
 	; /* do nothing */
     else if (State & CMDLINE)
-	redrawcmdline();
+    {
+	/* Redrawing only works when the screen didn't scroll. */
+	if (msg_scrolled == 0)
+	{
+	    update_screen(0);
+	    compute_cmdrow();
+	}
+	else
+	{
+	    /* Redraw in the same position, so that the user can continue
+	     * editing the command. */
+	    compute_cmdrow();
+	    if (cmdline_row > msg_scrolled)
+		cmdline_row -= msg_scrolled;
+	    else
+		cmdline_row = 0;
+	}
+	redrawcmdline_ex(FALSE);
+    }
     else if (State & (NORMAL | INSERT))
     {
-	update_screen(0);
+	/* keep the command line if possible */
+	update_screen(VALID_NO_UPDATE);
 	setcursor();
     }
     cursor_on();
@@ -476,7 +510,7 @@ redrawWinline(
 }
 
 /*
- * update all windows that are editing the current buffer
+ * Update all windows that are editing the current buffer.
  */
     void
 update_curbuf(int type)
@@ -490,8 +524,9 @@ update_curbuf(int type)
  * of stuff from Filemem to ScreenLines[], and update curwin->w_botline.
  */
     void
-update_screen(int type)
+update_screen(int type_arg)
 {
+    int		type = type_arg;
     win_T	*wp;
     static int	did_intro = FALSE;
 #if defined(FEAT_SEARCH_EXTRA) || defined(FEAT_CLIPBOARD)
@@ -502,11 +537,18 @@ update_screen(int type)
     int		gui_cursor_col;
     int		gui_cursor_row;
 #endif
+    int		no_update = FALSE;
 
     /* Don't do anything if the screen structures are (not yet) valid. */
     if (!screen_valid(TRUE))
 	return;
 
+    if (type == VALID_NO_UPDATE)
+    {
+	no_update = TRUE;
+	type = 0;
+    }
+
     if (must_redraw)
     {
 	if (type < must_redraw)	    /* use maximal type */
@@ -539,6 +581,8 @@ update_screen(int type)
     ++display_tick;	    /* let syntax code know we're in a next round of
 			     * display updating */
 #endif
+    if (no_update)
+	++no_win_do_lines_ins;
 
     /*
      * if the screen was scrolled up when displaying a message, scroll it down
@@ -576,7 +620,8 @@ update_screen(int type)
 		    }
 		}
 	    }
-	    redraw_cmdline = TRUE;
+	    if (!no_update)
+		redraw_cmdline = TRUE;
 #ifdef FEAT_WINDOWS
 	    redraw_tabline = TRUE;
 #endif
@@ -748,6 +793,9 @@ update_screen(int type)
     if (clear_cmdline || redraw_cmdline)
 	showmode();
 
+    if (no_update)
+	--no_win_do_lines_ins;
+
     /* May put up an introductory message when not editing a file */
     if (!did_intro)
 	maybe_intro_message();
@@ -9475,6 +9523,11 @@ win_do_lines(
     if (!redrawing() || line_count <= 0)
 	return FAIL;
 
+    /* When inserting lines would result in loss of command output, just redraw
+     * the lines. */
+    if (no_win_do_lines_ins && !del)
+	return FAIL;
+
     /* only a few lines left: redraw is faster */
     if (mayclear && Rows - line_count < 5
 #ifdef FEAT_WINDOWS
@@ -9482,7 +9535,8 @@ win_do_lines(
 #endif
 	    )
     {
-	screenclear();	    /* will set wp->w_lines_valid to 0 */
+	if (!no_win_do_lines_ins)
+	    screenclear();	    /* will set wp->w_lines_valid to 0 */
 	return FAIL;
     }
 
@@ -9498,10 +9552,12 @@ win_do_lines(
     }
 
     /*
-     * when scrolling, the message on the command line should be cleared,
+     * When scrolling, the message on the command line should be cleared,
      * otherwise it will stay there forever.
+     * Don't do this when avoiding to insert lines.
      */
-    clear_cmdline = TRUE;
+    if (!no_win_do_lines_ins)
+	clear_cmdline = TRUE;
 
     /*
      * If the terminal can set a scroll region, use that.