patch 8.2.4718: @@@ in the last line sometimes drawn in the wrong place

Problem:    @@@ in the last line sometimes drawn in the wrong place.
Solution:   Make sure the column is valid. (closes #10130)

src/drawscreen.c

@@ -2617,8 +2617,8 @@ win_update(win_T *wp)
 	    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, wp->w_wincol,
+	    screen_puts_len((char_u *)"@@", wp->w_width > 2 ? 2 : wp->w_width,
-							      HL_ATTR(HLF_AT));
+				       scr_row, wp->w_wincol, HL_ATTR(HLF_AT));
 	    screen_fill(scr_row, scr_row + 1,
 		    (int)wp->w_wincol + 2, (int)W_ENDCOL(wp),
 		    '@', ' ', HL_ATTR(HLF_AT));
@@ -2627,10 +2627,13 @@ win_update(win_T *wp)
 	}
 	else if (dy_flags & DY_LASTLINE)	// 'display' has "lastline"
 	{
+	    int start_col = (int)W_ENDCOL(wp) - 3;
+
 	    // Last line isn't finished: Display "@@@" at the end.
 	    screen_fill(W_WINROW(wp) + wp->w_height - 1,
 		    W_WINROW(wp) + wp->w_height,
-		    (int)W_ENDCOL(wp) - 3, (int)W_ENDCOL(wp),
+		    start_col < wp->w_wincol ? wp->w_wincol : start_col,
+		    (int)W_ENDCOL(wp),
 		    '@', '@', HL_ATTR(HLF_AT));
 	    set_empty_rows(wp, srow);
 	    wp->w_botline = lnum;

src/screen.c

@@ -2331,9 +2331,9 @@ space_to_screenline(int off, int attr)
 }
 
 /*
- * Fill the screen from 'start_row' to 'end_row', from 'start_col' to 'end_col'
+ * Fill the screen from "start_row" to "end_row" (exclusive), from "start_col"
- * with character 'c1' in first column followed by 'c2' in the other columns.
+ * to "end_col" (exclusive) with character "c1" in first column followed by
- * Use attributes 'attr'.
+ * "c2" in the other columns.  Use attributes "attr".
  */
     void
 screen_fill(

src/testdir/dumps/Test_display_lastline_1.dump

@@ -0,0 +1,10 @@
+>a+0&#ffffff0||+1&&|a+0&&@2| @69
+|a||+1&&|b+0&&@72
+|a||+1&&|b+0&&@26| @45
+|b||+1&&|~+0#4040ff13&| @71
+|b+0#0000000&||+1&&|~+0#4040ff13&| @71
+|b+0#0000000&||+1&&|~+0#4040ff13&| @71
+|b+0#0000000&||+1&&|~+0#4040ff13&| @71
+|@||+1#0000000&|~+0#4040ff13&| @71
+|<+3#0000000&| |[+1&&|N|o| |N|a|m|e|]| |[|+|]| @41|1|,|1| @11|A|l@1
+| +0&&@74

src/testdir/dumps/Test_display_lastline_2.dump

@@ -0,0 +1,10 @@
+>a+0&#ffffff0||+1&&|a+0&&@2| @69
+|a||+1&&|b+0&&@72
+|a||+1&&|b+0&&@26| @45
+|b||+1&&|~+0#4040ff13&| @71
+|b+0#0000000&||+1&&|~+0#4040ff13&| @71
+|b+0#0000000&||+1&&|~+0#4040ff13&| @71
+|b+0#0000000&||+1&&|~+0#4040ff13&| @71
+|@||+1#0000000&|~+0#4040ff13&| @71
+|<+3#0000000&| |[+1&&|N|o| |N|a|m|e|]| |[|+|]| @41|1|,|1| @11|A|l@1
+|:+0&&|s|e|t| |d|i|s|p|l|a|y|=|l|a|s|t|l|i|n|e| @53

src/testdir/dumps/Test_display_lastline_3.dump

@@ -0,0 +1,10 @@
+>a+0&#ffffff0@2| @69||+1&&|a+0&&
+|b@72||+1&&|a+0&&
+|b@26| @45||+1&&|a+0&&
+|~+0#4040ff13&| @71||+1#0000000&|b+0&&
+|~+0#4040ff13&| @71||+1#0000000&|b+0&&
+|~+0#4040ff13&| @71||+1#0000000&|b+0&&
+|~+0#4040ff13&| @71||+1#0000000&|b+0&&
+|~+0#4040ff13&| @71||+1#0000000&|@+0#4040ff13&
+|[+3#0000000&|N|o| |N|a|m|e|]| |[|+|]| @41|1|,|1| @11|A|l@1| |<+1&&
+|:+0&&|1|0@1|w|i|n|c|m|d| |>| @62

src/testdir/dumps/Test_display_lastline_4.dump

@@ -0,0 +1,10 @@
+>a+0&#ffffff0@2| @69||+1&&|a+0&&
+|b@72||+1&&|a+0&&
+|b@26| @45||+1&&|a+0&&
+|~+0#4040ff13&| @71||+1#0000000&|b+0&&
+|~+0#4040ff13&| @71||+1#0000000&|b+0&&
+|~+0#4040ff13&| @71||+1#0000000&|b+0&&
+|~+0#4040ff13&| @71||+1#0000000&|b+0&&
+|~+0#4040ff13&| @71||+1#0000000&|@+0#4040ff13&
+|[+3#0000000&|N|o| |N|a|m|e|]| |[|+|]| @41|1|,|1| @11|A|l@1| |<+1&&
+|:+0&&|s|e|t| |d|i|s|p|l|a|y|=|t|r|u|n|c|a|t|e| @53

src/testdir/test_display.vim

@@ -372,5 +372,31 @@ func Test_display_linebreak_breakat()
   let &breakat=_breakat
 endfunc
 
+func Test_display_lastline()
+  CheckScreendump
+
+  let lines =<< trim END
+      call setline(1, ['aaa', 'b'->repeat(100)])
+      set display=truncate
+      vsplit
+      100wincmd <
+  END
+  call writefile(lines, 'XdispLastline')
+  let buf = RunVimInTerminal('-S XdispLastline', #{rows: 10})
+  call VerifyScreenDump(buf, 'Test_display_lastline_1', {})
+
+  call term_sendkeys(buf, ":set display=lastline\<CR>")
+  call VerifyScreenDump(buf, 'Test_display_lastline_2', {})
+
+  call term_sendkeys(buf, ":100wincmd >\<CR>")
+  call VerifyScreenDump(buf, 'Test_display_lastline_3', {})
+
+  call term_sendkeys(buf, ":set display=truncate\<CR>")
+  call VerifyScreenDump(buf, 'Test_display_lastline_4', {})
+
+  call StopVimInTerminal(buf)
+  call delete('XdispLastline')
+endfunc
+
 
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4718,
 /**/
     4717,
 /**/