fix(ui): fix tabs not being spaced properly after virtual text with no wrap

also fixes incorrect skipping of multibyte characters

src/nvim/drawline.c

@@ -969,8 +969,7 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool nochange,
   int n_skip = 0;                       // nr of chars to skip for 'nowrap' or
                                         // concealing
   int skip_cells = 0;                   // nr of cells to skip for virtual text
-                                        // after the line, when w_skipcol is
+  int skipped_cells = 0;                // nr of skipped virtual text cells
-                                        // larger than the text length
 
   int fromcol_prev = -2;                // start of inverting after cursor
   bool noinvcur = false;                // don't invert the cursor
@@ -1786,14 +1785,22 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool nochange,
           // If the text didn't reach until the first window
           // column we need to skip cells.
           if (skip_cells > 0) {
-            if (wlv.n_extra > skip_cells) {
+            int virt_text_len = n_attr;
-              wlv.n_extra -= skip_cells;
+            if (virt_text_len > skip_cells) {
-              wlv.p_extra += skip_cells;
+              int len = mb_charlen2bytelen(wlv.p_extra, skip_cells);
+              wlv.n_extra -= len;
+              wlv.p_extra += len;
+              n_attr -= skip_cells;
+              // Skipped cells needed to be accounted for in vcol.
+              skipped_cells += skip_cells;
               skip_cells = 0;
             } else {
               // the whole text is left of the window, drop
               // it and advance to the next one
-              skip_cells -= wlv.n_extra;
+              skip_cells -= virt_text_len;
+              // Skipped cells needed to be accounted for in vcol.
+              skipped_cells += virt_text_len;
+              n_attr = 0;
               wlv.n_extra = 0;
             }
           }
@@ -2969,6 +2976,13 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool nochange,
       n_skip--;
     }
 
+    // The skipped cells need to be accounted for in vcol.
+    if (wlv.draw_state > WL_STC
+        && skipped_cells > 0) {
+      wlv.vcol += skipped_cells;
+      skipped_cells = 0;
+    }
+
     // Only advance the "wlv.vcol" when after the 'number' or
     // 'relativenumber' column.
     if (wlv.draw_state > WL_STC

src/nvim/mbyte.c

@@ -2024,6 +2024,24 @@ int mb_charlen(const char *str)
   return count;
 }
 
+int mb_charlen2bytelen(const char *str, int charlen)
+{
+  const char *p = str;
+  int count = 0;
+
+  if (p == NULL) {
+    return 0;
+  }
+
+  for (int i = 0; *p != NUL && i < charlen; i++) {
+    int b = utfc_ptr2len(p);
+    p += b;
+    count += b;
+  }
+
+  return count;
+}
+
 /// Like mb_charlen() but for a string with specified length.
 int mb_charlen_len(const char *str, int len)
 {

test/functional/ui/decorations_spec.lua

@@ -1793,6 +1793,31 @@ bbbbbbb]])
                                                         |
       ]]}
   end)
+
+  it('tabs are the correct length with no wrap following virtual text', function()
+    command('set nowrap')
+    feed('itest<TAB>a<ESC>')
+    meths.buf_set_extmark(0, ns, 0, 0,
+      { virt_text = { { string.rep('a', 55), 'Special' } }, virt_text_pos = 'inline' })
+    feed('gg$')
+    screen:expect { grid = [[
+      {28:aaaaaaaaaaaaaaaaaaaaaaaaa}test     ^a               |
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+      {1:~                                                 }|
+                                                        |
+      ]]}
+  end)
 end)
 
 describe('decorations: virtual lines', function()