Fix #3479: add latex support for docutils table stub columns

This implementation in latex writer allows arbitrary columns to be
declared "stub columns". But currently Docutils option
``:stub-columns:`` only allows a number telling the how many initial
columns are "stub columns".

tests/roots/test-latex-table/longtable.rst

@@ -130,3 +130,22 @@ longtable having problematic cell
      - cell2-2
    * - cell3-1
      - cell3-2
+
+longtable having both stub columns and problematic cell
+-------------------------------------------------------
+
+.. list-table::
+   :class: longtable
+   :header-rows: 1
+   :stub-columns: 2
+
+   * - header1
+     - header2
+     - header3
+   * - + instub1-1a
+       + instub1-1b
+     - instub1-2
+     - notinstub1-3
+   * - cell2-1
+     - cell2-2
+     - cell2-3

tests/roots/test-latex-table/tabular.rst

@@ -133,3 +133,21 @@ table having problematic cell
      - cell2-2
    * - cell3-1
      - cell3-2
+
+table having both stub columns and problematic cell
+---------------------------------------------------
+
+.. list-table::
+   :header-rows: 1
+   :stub-columns: 2
+
+   * - header1
+     - header2
+     - header3
+   * - + instub1-1a
+       + instub1-1b
+     - instub1-2
+     - notinstub1-3
+   * - cell2-1
+     - cell2-2
+     - cell2-3

tests/test_build_latex.py

@@ -916,6 +916,13 @@ def test_latex_table_tabulars(app, status, warning):
     table = tables['table having both :widths: and problematic cell']
     assert ('\\begin{tabular}[t]{|\\X{30}{100}|\\X{70}{100}|}' in table)
 
+    # table having both stub columns and problematic cell
+    table = tables['table having both stub columns and problematic cell']
+    assert ('&\\sphinxstylethead{\\sphinxstyletheadfamily \n'
+            'instub1-2\n\\unskip}\\relax &\nnotinstub1-3\n\\\\\n'
+            '\\hline\\sphinxstylethead{\\sphinxstyletheadfamily \n'
+            'cell2-1\n\\unskip}\\relax &' in table)
+
 
 @pytest.mark.skipif(docutils.__version_info__ < (0, 13),
                     reason='docutils-0.13 or above is required')
@@ -982,6 +989,13 @@ def test_latex_table_longtable(app, status, warning):
     table = tables['longtable having both :widths: and problematic cell']
     assert ('\\begin{longtable}{|\\X{30}{100}|\\X{70}{100}|}' in table)
 
+    # longtable having both stub columns and problematic cell
+    table = tables['longtable having both stub columns and problematic cell']
+    assert ('&\\sphinxstylethead{\\sphinxstyletheadfamily \n'
+            'instub1-2\n\\unskip}\\relax &\nnotinstub1-3\n\\\\\n'
+            '\\hline\\sphinxstylethead{\\sphinxstyletheadfamily \n'
+            'cell2-1\n\\unskip}\\relax &' in table)
+
 
 @pytest.mark.skipif(docutils.__version_info__ < (0, 13),
                     reason='docutils-0.13 or above is required')