vim-patch:9.1.1922: Wrong virtcol('$') with virtual text at EOL (#36643)

Problem:  Wrong virtcol('$') with virtual text at EOL (rickhowe).
Solution: Also add 1 to end virtcol when there is virtual text.
          (zeertzjq)

fixes: vim/vim#18761
closes: vim/vim#18762

d434f6c2a5

src/nvim/plines.c

@@ -551,9 +551,10 @@ void getvcol(win_T *wp, pos_T *pos, colnr_T *start, colnr_T *cursor, colnr_T *en
   } else {
     while (true) {
       char_size = charsize_regular(&csarg, ci.ptr, vcol, ci.chr.value);
+      // make sure we don't go past the end of the line
       if (*ci.ptr == NUL) {
-        // if cursor is at NUL, it is treated like 1 cell char unless there is virtual text
-        char_size.width = MAX(1, csarg.cur_text_width_left + csarg.cur_text_width_right);
+        // NUL at end of line only takes one column unless there is virtual text
+        char_size.width = 1 + csarg.cur_text_width_left + csarg.cur_text_width_right;
         on_NUL = true;
         break;
       }

test/functional/ui/decorations_spec.lua

@@ -5872,6 +5872,17 @@ describe('decorations: inline virtual text', function()
                                                         |
     ]])
   end)
+
+  it("virtcol('$') is correct with inline virt text at EOL", function()
+    insert(('1234567890\n'):rep(6))
+    for _, v in ipairs({ { 2, 'a' }, { 3, 'ab' }, { 4, 'abc' }, { 5, 'abcd' }, { 6, 'αβγ口' } }) do
+      local ln, tx = unpack(v)
+      local co = fn.col({ ln, '$' })
+      eq(11, fn.virtcol({ ln, '$' }))
+      api.nvim_buf_set_extmark(0, ns, ln - 1, co - 1, { virt_text = { { tx } }, virt_text_pos = 'inline' })
+      eq(11 + fn.strwidth(tx), fn.virtcol({ ln, '$' }))
+    end
+  end)
 end)
 
 describe('decorations: virtual lines', function()