latex tables: Fix rendering for grid filled merged vertical cells (#14024)

Co-authored-by: Jean-François B. <2589111+jfbu@users.noreply.github.com>

Author: tim-nordell-nimbelink

CHANGES.rst

@@ -20,6 +20,9 @@ Features added
 Bugs fixed
 ----------
 
+* LaTeX: Fix rendering for grid filled merged vertical cell
+  (PR #14024).
+  Patch by Tim Nordell
 * #14189: autodoc: Fix duplicate ``:no-index-entry:`` for modules.
   Patch by Adam Turner
 * #13713: Fix compatibility with MyST-Parser.

sphinx/writers/latex.py

@@ -1298,9 +1298,10 @@ def visit_row(self, node: Element) -> None:
                 # insert suitable strut for equalizing row heights in given multirow
                 self.body.append(r'\sphinxtablestrut{%d}' % cell.cell_id)
             else:  # use \multicolumn for wide multirow cell
+                left_colsep = _colsep if cell.col == 0 else ''
                 self.body.append(
                     r'\multicolumn{%d}{%sl%s}{\sphinxtablestrut{%d}}'
-                    % (cell.width, _colsep, _colsep, cell.cell_id)
+                    % (cell.width, left_colsep, _colsep, cell.cell_id)
                 )
 
     def depart_row(self, node: Element) -> None: