patch 8.2.4497: wrong color for half of wide character next to pum scrollbar

Problem:    Wrong color for half of wide character next to pum scrollbar.
Solution:   Redraw the screen cell with the right color. (closes #9874)

src/screen.c

@@ -1495,8 +1495,9 @@ screen_puts_len(
     int		textlen,
     int		row,
     int		col,
-    int		attr)
+    int		attr_arg)
 {
+    int		attr = attr_arg;
     unsigned	off;
     char_u	*ptr = text;
     int		len = textlen;
@@ -1722,8 +1723,10 @@ screen_puts_len(
 	    if (clear_next_cell)
 	    {
 		// This only happens at the end, display one space next.
+		// Keep the attribute from before.
 		ptr = (char_u *)" ";
 		len = -1;
+		attr = ScreenAttrs[off];
 	    }
 	}
 	else

src/testdir/dumps/Test_scrollbar_on_wide_char.dump

@@ -0,0 +1,10 @@
+|a+0&#ffffff0@1|0|b@1> @69
+|a+0#0000001#e0e0e08@1|0|b@1| @9| +0#0000000#0000001|啊*0&#ffffff0| +&@56
+|a+0#0000001#ffd7ff255@1|1|b@1| @9| +0#0000000#0000001| +0&#ffffff0|哦*&| +&@55
+|a+0#0000001#ffd7ff255@1|2|b@1| @9| +0#0000000#0000001|呃*0&#ffffff0@1| +&@54
+|a+0#0000001#ffd7ff255@1|3|b@1| @9| +0#0000000#0000001| +0&#ffffff0@58
+|a+0#0000001#ffd7ff255@1|4|b@1| @9| +0#0000000#0000001| +0&#ffffff0@58
+|a+0#0000001#ffd7ff255@1|5|b@1| @9| +0#0000000#0000001| +0&#ffffff0@58
+|a+0#0000001#ffd7ff255@1|6|b@1| @9| +0#0000000#a8a8a8255| +0&#ffffff0@58
+|a+0#0000001#ffd7ff255@1|7|b@1| @9| +0#0000000#a8a8a8255| +0&#ffffff0@58
+|-+2&&@1| |K|e|y|w|o|r|d| |c|o|m|p|l|e|t|i|o|n| |(|^|N|^|P|)| |m+0#00e0003&|a|t|c|h| |1| |o|f| |1|0| +0#0000000&@32

src/testdir/test_ins_complete.vim

@@ -606,6 +606,24 @@ func Test_pum_with_preview_win()
   call delete('Xpreviewscript')
 endfunc
 
+func Test_scrollbar_on_wide_char()
+  CheckScreendump
+
+  let lines =<< trim END
+    call setline(1, ['a', '            啊啊啊',
+                        \ '             哦哦哦',
+                        \ '              呃呃呃'])
+    call setline(5, range(10)->map({i, v -> 'aa' .. v .. 'bb'}))
+  END
+  call writefile(lines, 'Xwidescript')
+  let buf = RunVimInTerminal('-S Xwidescript', #{rows: 10})
+  call term_sendkeys(buf, "A\<C-N>")
+  call VerifyScreenDump(buf, 'Test_scrollbar_on_wide_char', {})
+
+  call StopVimInTerminal(buf)
+  call delete('Xwidescript')
+endfunc
+
 " Test for inserting the tag search pattern in insert mode
 func Test_ins_compl_tag_sft()
   call writefile([

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4497,
 /**/
     4496,
 /**/