fix(ui): fix multi-byte characters highlight in virtual text

This also fixes insert cursor position around virtual text

vim-patch:9.0.0132: multi-byte characters in virtual text not handled correctly

Problem:    Multi-byte characters in virtual text not handled correctly.
Solution:   Count screen cells instead of bytes.

09ff4b54fb

src/nvim/charset.c

@@ -1079,8 +1079,10 @@ void getvcol(win_T *wp, pos_T *pos, colnr_T *start, colnr_T *cursor, colnr_T *en
   }
 
   if (cursor != NULL) {
+    if ((State & MODE_INSERT) == 0) {
       // cursor is after inserted text
       vcol += cts.cts_cur_text_width;
+    }
     if ((*ptr == TAB)
         && (State & MODE_NORMAL)
         && !wp->w_p_list

src/nvim/drawline.c

@@ -1824,7 +1824,7 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool nochange,
           wlv.c_extra = NUL;
           wlv.c_final = NUL;
           wlv.extra_attr = vtc.hl_id ? syn_id2attr(vtc.hl_id) : 0;
-          n_attr = wlv.n_extra;
+          n_attr = mb_charlen(vtc.text);
           extmark_attr = 0;
           virt_inline_i++;
         }

test/functional/ui/decorations_spec.lua

@@ -1295,8 +1295,78 @@ end]]
       {1:~                                                 }|
       {1:~                                                 }|
                                                         |
-      ]]
+      ]]}
-        }
+  end)
+
+  it('has correct highlighting with multi-byte characters in inline virtual text', function()
+    insert('12345678')
+    meths.buf_set_extmark(0, ns, 0, 4,
+            { virt_text = { { 'múlti-byté chñröcters 修补', 'Special' } }, virt_text_pos = 'inline' })
+
+    screen:expect { grid = [[
+      1234{28:múlti-byté chñröcters 修补}567^8                |
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+                                                        |
+      ]]}
+  end)
+
+  it('has correct cursor position when inserting around virtual text', function()
+    insert('12345678')
+    meths.buf_set_extmark(0, ns, 0, 4,
+            { virt_text = { { 'virtual text', 'Special' } }, virt_text_pos = 'inline' })
+    feed '^'
+    feed '3l'
+    feed 'a'
+    screen:expect { grid = [[
+      1234{28:^virtual text}5678                              |
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {24:-- INSERT --}                                      |
+      ]]}
+    feed '<ESC>'
+    feed '^'
+    feed '4l'
+    feed 'i'
+    screen:expect { grid = [[
+      1234{28:^virtual text}5678                              |
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {24:-- INSERT --}                                      |
+      ]]}
   end)
 end)