patch 9.1.0815: "above" virtual text causes wrong 'colorcolumn' position

Problem:  "above" virtual text causes wrong 'colorcolumn' position.
          (@matrdr)
Solution: Use the number of cells instead of bytes for vcol_off_tp.
          (zeertzjq)

fixes: #15946
closes: #15948

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/drawline.c

@@ -2263,7 +2263,7 @@ win_line(
 				}
 
 				if (above)
-				    wlv.vcol_off_tp = wlv.n_extra;
+				    wlv.vcol_off_tp = vim_strsize(wlv.p_extra);
 
 				if (lcs_eol_one < 0
 					&& wp->w_p_wrap

src/testdir/dumps/Test_prop_multibyte_above_1.dump

@@ -0,0 +1,16 @@
+| +0#af5f00255#ffffff0@3|…+0#0000001#ffff4012| +0#0000000#ffffff0@54
+| +0#af5f00255&@1|1| |1+0#0000000&@7| | +0&#ffd7d7255| +0&#ffffff0@45
+| +0#af5f00255&@3|…+0#0000001#ffff4012| +0#0000000#ffffff0@54
+| +0#af5f00255&@1|2| | +0#0000000&@8| +0&#ffd7d7255| +0&#ffffff0@45
+| +0#af5f00255&@3|…+0#0000001#ffff4012| +0#0000000#ffffff0@54
+| +0#af5f00255&@1|3| |3+0#0000000&@8| +0&#ffd7d7255| +0&#ffffff0@45
+| +0#af5f00255&@3|…+0#0000001#ffff4012| +0#0000000#ffffff0@54
+| +0#af5f00255&@1|4| | +0#0000000&@8| +0&#ffd7d7255| +0&#ffffff0@45
+| +0#af5f00255&@3|…+0#0000001#ffff4012| +0#0000000#ffffff0@54
+| +0#af5f00255&@1|5| >5+0#0000000&@8|5+0&#ffd7d7255|5+0&#ffffff0| @44
+|~+0#4040ff13&| @58
+|~| @58
+|~| @58
+|~| @58
+|~| @58
+| +0#0000000&@41|5|,|1|-|5|7| @7|A|l@1| 

src/testdir/test_textprop.vim

@@ -3203,6 +3203,27 @@ func Test_prop_with_text_above_below_empty()
   call StopVimInTerminal(buf)
 endfunc
 
+func Test_prop_with_multibyte_above()
+  CheckRunVimInTerminal
+
+  let lines =<< trim END
+      setlocal number colorcolumn=10
+      call setline(1, ['11111111', '', '333333333', '', '55555555555'])
+
+      let vt = 'test'
+      call prop_type_add(vt, {'highlight': 'ToDo'})
+      for ln in range(1, line('$'))
+        call prop_add(ln, 0, {'type': vt, 'text': '…', 'text_align': 'above'})
+      endfor
+      normal G
+  END
+  call writefile(lines, 'XscriptPropMultibyteAbove', 'D')
+  let buf = RunVimInTerminal('-S XscriptPropMultibyteAbove', #{rows: 16, cols: 60})
+  call VerifyScreenDump(buf, 'Test_prop_multibyte_above_1', {})
+
+  call StopVimInTerminal(buf)
+endfunc
+
 func Test_prop_with_multibyte_below()
   CheckRunVimInTerminal
 

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    815,
 /**/
     814,
 /**/