Col-span and row-span in LaTeX reader

[LaurentRDC]

Hello,

This is a PR for better table support in the LaTeX reader that closes #6311.

This PR adds support for table cells that span more than a single row and single column, as is now supported in pandoc-types 1.21.

So far, this PR supports the \multicolumn and \multirow (from multirow package) commands, as well as nesting them.

Here are usage examples:

Multicolumn:

\begin{table}
    \begin{tabular}{ c c c }
    \multicolumn{2}{c}{1} & 2 \\
    \end{tabular}
    \caption{Caption}
\end{table}

Native output:

[Table ("",[],[]) (Caption Nothing
 [Plain [Str "Caption"]])
 [(AlignCenter,ColWidthDefault)
 ,(AlignCenter,ColWidthDefault)
 ,(AlignCenter,ColWidthDefault)]
 (TableHead ("",[],[])
 [])
 [(TableBody ("",[],[]) (RowHeadColumns 0)
  []
  [Row ("",[],[])
   [Cell ("",[],[]) AlignCenter (RowSpan 1) (ColSpan 2) 
    [Para [Str "1"]]
   ,Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
    [Plain [Str "2"]]]])]
 (TableFoot ("",[],[])
 [])]

Nesting \multirow and \multicolumn into a 2x2 cell:

\begin{table}
    \begin{tabular}{ c c c c }
        % 2x2 cell
        \multirow{2}{|c|}{\multicolumn{2}{|c|}{1}} & 2 & 3 \\
                                                     4 & 5 \\
    \end{tabular}
    \caption{Caption}
\end{table}

Native output:

[Table ("",[],[]) (Caption Nothing
 [Plain [Str "Caption"]])
 [(AlignCenter,ColWidthDefault)
 ,(AlignCenter,ColWidthDefault)
 ,(AlignCenter,ColWidthDefault)
 ,(AlignCenter,ColWidthDefault)]
 (TableHead ("",[],[])
 [])
 [(TableBody ("",[],[]) (RowHeadColumns 0)
  []
  [Row ("",[],[])
   [Cell ("",[],[]) AlignCenter (RowSpan 2) (ColSpan 2) 
    [Para [Str "1"]]
   ,Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
    [Plain [Str "2"]]
   ,Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
    [Plain [Str "3"]]]
  ,Row ("",[],[])
   [Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
    [Plain [Str "4"]]
   ,Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
    [Plain [Str "5"]]]])]
 (TableFoot ("",[],[])
 [])]

[LaurentRDC]

This is ready for review at your earliest convenience @jgm @tarleb

[tarleb]

Thank you for the contribution, and sorry for the wait. I skimmed over it, looks good! I'll have a close look within the next days.

[tarleb]

See the inline comments, but looks good to me!

[tarleb]

👍

[LaurentRDC]

Is there a reason to wait before merging?

[jgm]

This looks good to me and I'll merge it now, thank you.
But does it completely close #6311? For that, we should:

• attach an identifier to table attributes if a label is present
• possibly: handle multiple header rows? (I suppose we could identify them by hline or the booktabs equivalents)
• possibly: table head and foot?

I will keep #6311 open until these are done too.