patch 7.4.2109
Problem:    Setting 'display' to "lastline" is a drastic change, while
            omitting it results in lots of "@" lines.
Solution:   Add "truncate" to show "@@@" for a truncated line.
diff --git a/src/screen.c b/src/screen.c
index 1b364a4..b16bd87 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -2018,7 +2018,7 @@
 		    && wp->w_lines[idx].wl_valid
 		    && wp->w_lines[idx].wl_lnum == lnum
 		    && lnum > wp->w_topline
-		    && !(dy_flags & DY_LASTLINE)
+		    && !(dy_flags & (DY_LASTLINE | DY_TRUNCATE))
 		    && srow + wp->w_lines[idx].wl_size > wp->w_height
 #ifdef FEAT_DIFF
 		    && diff_check_fill(wp, lnum) == 0
@@ -2139,6 +2139,21 @@
 	    wp->w_filler_rows = wp->w_height - srow;
 	}
 #endif
+	else if (dy_flags & DY_TRUNCATE)	/* 'display' has "truncate" */
+	{
+	    int scr_row = W_WINROW(wp) + wp->w_height - 1;
+
+	    /*
+	     * Last line isn't finished: Display "@@@" in the last screen line.
+	     */
+	    screen_puts_len((char_u *)"@@", 2, scr_row, W_WINCOL(wp),
+							      hl_attr(HLF_AT));
+	    screen_fill(scr_row, scr_row + 1,
+		    (int)W_WINCOL(wp) + 2, (int)W_ENDCOL(wp),
+		    '@', ' ', hl_attr(HLF_AT));
+	    set_empty_rows(wp, srow);
+	    wp->w_botline = lnum;
+	}
 	else if (dy_flags & DY_LASTLINE)	/* 'display' has "lastline" */
 	{
 	    /*